Backoround

[0001] A printing device is an example of a device to transfer a substance from a reservoir to a substrate. The printing device may perform the mechanical operations to execute this transfer. As the supply of the substance (e.g., a printing substance) within a reservoir (e.g., a fluid ejection device) is exhausted, the reservoir may be refilled or may be removed from the printing device and replaced with a replacement reservoir. The printing device and the reservoir may communicate data to facilitate the operation of the printing device and/or the transfer of the printing substance. Data communication between the printing device and the reservoir may occur via electrical connections established between the reservoir and the printing device while the reservoir is connected to the printing device.

Brief Descriotion of the Drawinas

[0002] FIG. 1 is a diagram of an example optical data transmission system according to the present disclosure.

[0003] FIG. 2 is a diagram of an example optical data transmission fluid ejection device according to the present disclosure.

[0004] FIG. 3 is a diagram of an example optical data transmission printing device 302 according to the present disclosure.

[0005] FIG. 4A-FIG. 4C are sequential diagrams of an example optical data transmission printing device verifying a type of a fluid ejection device according to the present disclosure.

[0006] FIG. 5 is a diagram of an example optical data transmission printing device according to the present disclosure.

[0007] FIG. 6 is a diagram of an example optical data transmission method according to the present disclosure. Detailed Description

[0008] Returning to the example of a printing device, noted above, a printing device may be operated to transfer a printing substance (such as a printing fluid, a printing powder, a printing gel, etc.) from a fluid ejection device to a print medium (such as paper, products, cloth, plastics, etc.). For example, the printing device may position an ejection device and/or a dispensing nozzle associated with the fluid ejection device over a portion of the print medium and eject the printing substance from the fluid ejection device onto the printing medium at the portion. The printing device may reposition the fluid ejection device and/or its associated dispensing nozzle to another portion of the print medium and eject the printing substance from the fluid ejection device onto the printing medium at the other portion. For example, the printing device may move the fluid ejection device and/or its dispensing nozzle to various locations of the printing medium while the printing substance is ejected in order to reproduce a desired image, text, or object on the printing medium.

[0008] In order to transfer the printing substance to the appropriate portion of the print medium in a manner that faithfully reproduces a desired image, text, or object the printing device may rely on being able to accurately position and/or reposition the fluid ejection device and/or its associated dispensing nozzle. The printing device may utilize various motors and/or other mechanical components to position and/or reposition the fluid ejection device and/or its associated dispensing nozzle. However, the motors and/or other mechanical components may experience wear, suffer from degraded performance, and/or malfunction.

[0010] As such, the function of the various motors and/or other mechanical components may be monitored. For example, a stepper motor may be utilized to position or reposition the fluid ejection device and/or its associated nozzle while the fluid ejection device is connected to the printing device. A step counter to count the number of steps that the stepper motor performs while actuated in order to determine where the fluid ejection device and/or its associated nozzle are positioned relative to the printing device and/or the printing medium. However, as the mechanical component of the printing device begin to wear and tolerances begin to degrade, counting steps may not provide an accurate representation of where the fluid ejection device and/or its associated nozzle are relative to the printing device and/or the printing medium any longer. Further, while counting steps may be utilized to estimate where the ejection device and/or its associated nozzle should be, it may not, given the degradation of tolerances that degrade the correlation between steps and position, provide an accurate idea of where the ejection device and/or its associated nozzle actually is located. As such, the actual position of the ejection device and/or its associated nozzle, the condition and/or functioning of the mechanical components of the printing device, and/or whether a recalibration is in order for the mechanical components of the printing device involved in repositioning the fluid ejection device may not be accurately and reliably monitored.

[0011] Additionally, as mentioned above, the fluid ejection device may be a consumable component which may be used by and/or replaced within the printing device. For example, a fluid ejection device containing printing substance may be attached to the printing device (e.g., within a moveable carriage of the printing device). The printing substance may be ejected from the fluid ejection device by the printing device until the printing substance is exhausted (e.g., printing substance runs out, printing substance falls below a threshold amount, printing substance exceeds an expiration threshold, etc.). Once exhausted, the fluid ejection device may be removed from the printing device and replaced with a replacement fluid ejection device.

[0012] Removeable and/or replaceable fluid ejection devices may extend the life of the printing device beyond just the printing substance capacity of its reservoir and may prevent or reduce potentially messy and damaging manual reservoir refilling operations. However, with a variety of printing devices, a variety of fluid ejection devices, and/or a variety of printing substances available in the market, mechanisms ensuring compatibility between a particular fluid ejection device and a particular printing device may be employed to avoid damage to the printing device, avoid damage to the fluid ejection device, and/or to facilitate proper functioning of the printing device. Typically, coarse mechanical keying mechanisms are utilized to ensure compatibility by utilizing complementary geometries between fluid ejection device and printing carriage as a prerequisite for proper engagement between the fluid ejection device and printing carriage. However, such mechanisms may limit product geometries and may not prevent some erroneous pairings between fluid ejection devices and printing devices with “close enough” geometries.

[0013] Additionally, a printing device manufacturer may utilize mechanisms on the fluid ejection device and/or at the printing device to establish the authenticity of the fluid ejection device and/or the printing device. For example, an electronic chip including electronic circuitry to communicate with the printing device over electrical connections (e.g., wires, cabling, wirelessly, etc.) may be embedded in the fluid ejection device. The electronic circuitry may communicate, over the electrical connections, with the printing device regarding its authenticity, identification, amount of printing substance remaining, etc.

[0014] In contrast, examples consistent with the present disclosure include various mechanisms involving the optical transmission of data between a fluid ejection device and a printing device. The optical transmission of data may provide a secure communication channel outside of the electronic connections between the fluid ejection device and the printing device. The optical transmission of data may be utilized to verify the mechanical function of the printing device, verify characteristics of the fluid ejection device, and/or write data to the fluid ejection device. For example, a fluid ejection device may include: a photodetector to receive, upon alignment between a photodetector and a photoemitter of a printing device, optically transmitted data encoded as electromagnetic radiation emitted from the photoemitter; and a storage medium to store the optically transmitted data in the form of data queryable by the printing device.

[0015] The figures herein follow a numbering convention in which the first digit or digits correspond to the drawing figure number and the remaining digits identify an element or component in the drawing. Similar elements or components between the different figures may be identified by the use of similar digits. For example, 108 may reference element “08" in Figure 1, and a similar element may be referenced as 208 in Figure 2. Elements shown in the various figures herein can be added, exchanged, and/or eliminated so as to provide a number of additional examples of the present disclosure. In addition, the proportion and the relative scale of the elements provided in the figures are intended to illustrate the examples of the present disclosure and should not be taken in a limiting sense.

[0016] FIG. 1 is a diagram of an example optical data transmission system 100 according to the present disclosure. The described components and/or operations of the system 100 may include and/or be interchanged with the described components and/or operations described in relation to FIG. 2- FIG. 6.

[0017] The system 100 may include a device to transfer a substance from a reservoir to a substrate. For example, the system 100 may include a printing device 102. The printing device 102 may include an inkjet printer, a laser printer, an LED printer, a solid ink printer, a multi-function printer, a 3D printer, etc. The printing device 102 may be a commercial printer, a business printer, a home printer, etc. [0018] The printing device 102 may include a printer carriage 104 component. The printer carriage 104 may include an interface to engage with a fluid ejection device 106. For example, the printer carriage 104 may include an assembly that engages with the fluid ejection device 106 and retains the fluid ejection device 106 during operation of the printing device 102.

[0019] The printer carriage 104 may include a data communication interface. The data communication interface may include an interface to communicatively couple the printing device 102 to a fluid ejection device 106 attached to the printer carriage 104. In some examples, the data communication interface may include a portion of a non-physical data connection to the fluid ejection device 106. For example, the data communication interface may include a portion of a radio frequency data communication link, a Bluetooth data communication link, etc. between the printing device 102 and the fluid ejection device 106.

[0020] In other examples, the data communication interface may include a portion of a physical data connection between the printing device 102 and the fluid ejection device 106. For example, the printer carriage 104 may include an interface to establish an electrical connection with a complementary data communication interface on the fluid ejection device 106. The data communication interface of the printer carriage 104 may be an interface communicatively coupled to a control line 108 of the printing device 102. Data may be communicated from the printing device 102, across the control line 108, across the data communication interface of the printer carriage 104, across the complementary data communication interface of the fluid ejection device 106, and to the fluid ejection device 106 and vice versa. For example, the printer carriage 104 may include wires, pins, electrical contacts, etc. that physically interface with wires, pins, electrical contacts, etc. on the fluid ejection device 106 to communicatively couple the fluid ejection device 106 and the printing device 102 while the fluid ejection device 106 is engaged with the printer carriage 104.

[0021] The printer carriage 104 may be a moveable component of the printing device 102. For example, the printing device 102 may include mechanical components to move the printer carriage 104 within the printing device 102. For example, the printing device may include motors and controllers to move the printer carriage 104 within the printing device 102.

[0022] In some examples, the printer carriage 104 may be moveable within a carriageway 110 of the printing device 102. The carriageway 110 may include a void within the printing device 102, within which the printer carriage 104 may be moved.

In some examples, the printer carriage 104 may be moved within the carriageway 110 along and/or in contact with a guiding mechanism such as carriage guide rail 112.

[0023] The movement of the printer carriage 104 within the carriageway 110 may be utilized to align the printer carriage 104 with various portions of a printing medium passing in proximity to the printer carriage 104 during a printing operation. The printer carriage 104 may be moved along and/or across the surface of the printing medium to align the printer carriage 104 with the printable portions of the printing medium.

[0024] Since the fluid ejection device 106 may be engaged with the printer carriage 104, movement of the printer carriage 104 may also move the fluid ejection device 106 engaged therewith. As such, the movement of the printer carriage 104 within the carriageway 110 may be utilized to align the fluid ejection device 106 with various portions of a printing medium. For example, the printing medium may be passed in proximity to the printer carriage 104 and/or the fluid ejection device 106 during a printing operation to facilitate the transfer of printing substance from the fluid ejection device 106 to the printing medium. The printer carriage 104 may be moved along and/or across the surface of the printing medium to align the fluid ejection device 106, including nozzles through which a printing substance within the fluid ejection device 106 may be ejected, with the printable portions of the printing medium. The printing substance within the fluid ejection device 106 may be ejected from the fluid ejection device 106 onto a first portion of a printing medium, then the printer carriage 104 may be moved within the carriageway 110 to align the fluid ejection device 106 with a second portion of the printing medium where additional printing substance from within the fluid ejection device 106 may be ejected on to the printing medium.

[0025] Additionally, the printer carriage 104 may be moved to a service position. For example, the printer carriage 104 may be moved to position the fluid ejection device 106 proximate to a servicing station. The servicing station may be utilized to clean and/or calibrate the fluid ejection device 106, nozzles utilized in ejecting the printing substance from the fluid ejection device 106, and/or the printer carriage 104.

[0026] The printing device 102 may include a photoemitter 114. The photoemitter 114 may include a component that emits electromagnetic radiation into the environment. The photoemitter 114 may include a component that directionally emits the electromagnetic radiation. For example, the photoemitter 114 may emit the electromagnetic radiation in a particular direction and avoid a widespread or far reaching emission that escapes in multiple directions. Instead, the emission field of the photoemitter 114 may be directional and substantially concentrated (e.g., by mechanical occlusion, beam shaping, power of emissions, etc.) within an area immediately proximate to the photoemitter 114.

[0027] The photoemitter 114 may include a component that emits electromagnetic radiation from a portion of the electromagnetic spectrum. For example, the photoemitter 114 may include a component that emits electromagnetic radiation from the visible light portion, the infrared light portion, the X-ray portion, etc. of the electromagnetic spectrum. For example, the photoemitter 114 may be a source of such electromagnetic radiation. In some examples, the photoemitter 114 may include a light source. For example, the photoemitter 114 may include a light emitting diode (LED).

[0028] The photoemitter 114 may be able to emit electromagnetic radiation with a plurality of wave frequencies (e.g., wavelength intervals and/or frequency intervals). For example, the photoemitter 114 may be able to modulate the wavelength intervals and/or frequency intervals of the electromagnetic radiation that it is emitting. In an example, an LED photoemitter 114 may modulate its electromagnetic radiation emission between 700-635 nm wavelength interval, 430- 480 THz frequency interval (e.g., to emit red light) and 490-450nm wavelength interval, 610-670 THz frequency interval (e.g., to emit blue light).

[0029] Additionally, the photoemitter 114 may be able to emit electromagnetic radiation with a plurality of periodicities. For example, the photoemitter 114 may be able to modulate the periodicity of its electromagnetic radiation emissions. In an example, an LED photoemitter 114 may emit visible light pulses that last half a microsecond (ps) and occur every ps. [0030] The illustrated location of the photoemitter 114 is a non-limiting example of a location of the photoemitter 114. The photoemitter 114 may be located at any location on the printing device 102 and/or its constituent components where it is oriented to emit its electromagnetic radiation emissions into the carriageway 110. For example, the photoemitter 114 is illustrated on a bottom wall of the printing device, but the photoemitter 114 may be located on a side wall, a backwall, a top wall, a front wall, and/or any surface which orients the photoemitter 114 to directionally emit its electromagnetic radiation into a portion of the carriageway 110. Again, the emission of the photoemitter 114 into the carriageway 110 may be directional such that the emitted electromagnetic radiation is concentrated and/or isolated within a relatively small area that may approximately correspond to the area occupied by a corresponding photodetector (e.g., photodetector 116).

[0031] The printing device 102 may include more than one photoemitter 114. For example, the printing device 102 may include a plurality of photoemitters. In some examples, the plurality of photoemitters may be located at various locations along the carriageway 110. For example, photoemitters may be located at the two opposing extremes of the length of travel of the printer carriage 104 in the carriageway 110. In other examples, the photoemitters may be spaced at specific intervals along the carriageway 110.

[0032] As described above, the system 100 may include a fluid ejection device 106. The fluid ejection device 106 may be removeable from and/or replaceable within the printing device 102. The fluid ejection device 106 may engage with and/or be carried by the printer carriage. The fluid ejection device 106 may include a data communication interface complementary to the data communication interface of the printer carriage 104. As described above with respect to the data communication interface of the printer carriage 104, the data communication interface of the fluid ejection device may be a physical or non-physical data communication interface that is complementary to the one located at the printer carriage 104. For example, the fluid ejection device 106 may include wires, pins, electrical contacts, etc. that physically interface with wires, pins, electrical contacts, etc. on the printer carriage 104 to communicatively couple the fluid ejection device 106 and the printing device 102 while the fluid ejection device 106 is engaged with the printer carriage 104. [0033] The fluid ejection device 106 may be and/or include a reservoir holding printing substance to be ejected during a printing operation. In some examples, the fluid ejection device 106 may be a printing substance reservoir that is dimensioned to fit within the printer carriage 104. In such examples, the printer carriage 104 may include the ejector silicon and/or nozzles utilized in ejecting the printing substance from the fluid ejection device 106 on to the printing medium. For example, the ejector silicon and/or nozzles utilized in ejecting the printing substance from the fluid ejection device 106 may interface with and/or be supplied from the fluid ejection device 106, but may be a separate component from the fluid ejection device 106 that is resident upon the printer carriage 104.

[0034] In other examples, the fluid ejection device 106 may include a reservoir body and/or a printhead. For example, the fluid ejection device 106 may include a pen body (e.g., an inkjet pen body) and a fluidic die including electronic components (e.g., wire traces, bond pads, etc.), such as to provide an electrical connection to other components of the fluid ejection device 106. In some examples, the fluid ejection device 106 may include integrated ejector silicon and/or nozzles utilized in ejecting the printing substance from the fluid ejection device 106 onto a printing medium.

[0035] The fluid ejection device 106 may include a photodetector 116. The photodetector 116 may include a component that detects electromagnetic radiation, such as the electromagnetic radiation emitted by the photoemitter 114. For example, the photodetector 116 may include a component that can detect the electromagnetic radiation and covert the radiation to an electrical signal such as a current or a voltage. For example, the photodetector 116 may include a photodiode semiconductor device and/or a phototransistor that coverts light into an electrical current while photons are absorbed in the photodiode.

[0036] The illustrated location of the photodetector 116 is a non-limiting example of a location of the photodetector 116 on the fluid ejection device 106. The photodetector 116 may be located at any location on the fluid ejection device 106 and/or its constituent components where it is oriented to detect electromagnetic radiation emissions from a portion of the carriageway 110. For example, the photodetector 116 is illustrated on a bottom wall of the fluid ejection device 106, but the photodetector 116 may be located on a side wall, a backwall, a top wall, a front wall, and/or any other surface of the fluid ejection device 106 which orients the photodetector 116 to detect electromagnetic radiation directionally emitted by the photoemitter 114 into a portion of the carriageway 110. [0037] while aligned (e.g., by the movement of the printer carriage 104, attached to the fluid ejection device 106, through the carriageway 110) the photoemitter 114 and the photodetector 116 may form an optical data transmission path between the fluid ejection device 106 and the printing device 102. For example, upon being moved into the path of the electromagnetic radiation being directionally emitted into the carriageway 110 by the photoemitter 114, the electromagnetic radiation may become incident upon the photodetector 116 thereby establishing an optical data transmission path. An optical data transmission path may include a contactless data transmission path. For example, an optical data transmission path may transmit data between the fluid ejection device 106 and the printing device 102 without contact between the two and/or without transmission through a physical connection between the two. Instead, an optical data transmission path may transmit data via radiation sent through the air between the fluid ejection device 106 and the printing device 102. The optical data transmission path may be separate from the data communication interfaces described with respect to the data communication link between the printer carriage 104 and the fluid ejection device 106.

[0038] The photoemitter 114 may emit data encoded as electromagnetic radiation into the carriageway 110. In some examples, the identity of the bits of data may be encoded as modulations to the electromagnetic radiation emitted from the photoemitter 114.

[0039] For example, the photoemitter 114 may modulate the identity of a bit of data to be communicated via the optical data transmission path by modulating a periodicity of the electromagnetic radiation emissions from the photoemitter 114. In an example, the period of and/or between electromagnetic radiation emissions from the photoemitter 114 may communicate the identity of bits of data.

[0040] In some examples, the photoemitter 114 may modulate the identity of a bit of data to be communicated via the optical data transmission path by modulating the wave frequency of the electromagnetic radiation emissions from the photoemitter 114. In an example, the wave frequency of electromagnetic radiation emissions from the photoemitter 114 may communicate the identity of bits of data.

[0041] A photodetector 116 aligned within the path of the directional electromagnetic radiation emission from the photoemitter 114 may receive the modulated electromagnetic radiation emissions and convert the modulated electromagnetic radiation emissions to an electrical signal. As such, the fluid ejection device 106 may interpret the modulated electromagnetic radiation emissions, received from the photoemitter 114 via the photodetector 116, as bits of data identified by the modulations.

[0042] The optical data transmission path may, while alignment between the photoemitter 114 and the photodetector 116 is achieved, provide a secure mechanism for optical data communication that is separate from the other nonphysical and/or physical electrical connections connecting the printing device 102 to the fluid ejection device 106. For example, the optical data transmission path may be separate from the control line 108 linking the printing device 102 and the fluid ejection device 106. For example, the optical data transmission path is a separate and position-dependent communication link which does not utilize a control line 108 to communicate data between the printing device 102 and the fluid ejection device 106.

[0043] In some examples, the fluid ejection device 106 may include and/or be communicatively coupled to a storage medium. The storage medium may include a non-transitory machine-readable storage medium that may be utilized to store data. For example, the storage medium may be utilized to store the optically transmitted bits of data that are received from the photoemitter 114 via the photodetector 116.

[0044] As such, in some examples, the printing device 102 may write data to the fluid ejection device 106 via the optical data transmission path. For example, the printing device 102 may transmit a pen identification to be assigned to the fluid ejection device 106 by emitting electromagnetic radiation encoded with the pen identification into the carriageway 110 where an aligned photodetector 116 detects, coverts, and/or translates the electromagnetic radiation into the bits defining the pen identification. The pen identification may include an identification assigned to the fluid ejection device 106 for the purposes of identifying the fluid ejection device 106 during communications between the fluid ejection device 106 and the printing device 102. The pen identification may be written to the storage medium of the fluid ejection device 106. The fluid ejection device 106 may utilize and/or present the assigned pen identification going forward in sending and/or receiving commands and other communications. For example, if future commands from the printing device 102 received over the control line 108 are addressed to the assigned pen identification, the fluid ejection device 106 may respond to and/or execute those commands.

[0045] In addition, the data stored in the storage medium of the fluid ejection device 106 may be queryable by the printing device 102. For example, the data stored in the storage medium may be available to be queried and/or read by the printing device 102. For example, a printing device 102 may be able to submit a query to the fluid ejection device 106 and or its storage medium to determine the data stored at the storage medium.

[0046] For example, the printing device 102 may submit a data query via the control line 108 to the fluid ejection device 106. The query may be transmitted across the data communication interface of the printer carriage 104 and/or the complementary data communication interface of the fluid ejection device 106. The fluid ejection device 106 may respond to the query by reporting on the saved data contents of the storage medium. For example, the fluid ejection device 106 may send a copy of the data in the storage medium across the data communication interface of the fluid ejection device 106, across the complementary data communication interface of the printer carriage 104, across the control line 108, and to the printing device 102.

[0047] In this manner, the printing device 102 may transmit data to the fluid ejection device 106 via the optical data transmission link and then query the fluid ejection device 106 to see what data the fluid ejection device 106 actually received. As such, the printing device 102 may perform verifications of the identity, authenticity, type, etc. of the fluid ejection device 106.

[0048] Further, since the optical data transmission link between the photoemitter 114 and the photodetector 116 is alignment-dependent, the photoemitter 114 of the printing device 102 and the photodetector 116 of the fluid ejection device 106 may be utilized to verify and/or calibrate mechanical function of the printing device 102, the carriage 104, and/or the mechanical components involved in moving the carriage 104. For example, the printing device 102 may be able to verify the mechanical function of the carriage 104, motors that move the carriage 104, etc. utilizing the optical data transmission link between the photoemitter 114 and the photodetector 116.

[0049] In an example, the printing device 102 may cause the carriage 104 to be moved to a first position in the carriageway 110. The printing device 102 may cause data encoded as electromagnetic radiation to be directionally emitted from the photoemitter 114 into a portion of the carriageway 110 corresponding to the first position in the carriageway 110. The photodetector 116 of the fluid ejection device 106, assuming alignment with the photoemitter 114 in the right place at the right time, will receive the data. The data may be stored to a storage medium of the fluid ejection device 106. The storage medium of the fluid ejection device 106 may be queried over the control line 108 about the data transmitted from the photoemitter 114.

[0050] The printing device 102 may analyze a response to the query received from the fluid ejection device 106 across the control line 108. If the response to the query from the fluid ejection device 106 matches an expected response (e.g., the same data that was transmitted from the photoemitter 114), then the printing device 102 may determine that the fluid ejection device 106 and/or the carriage 104 that it is engaged with were in the expected place at the expected time. As such, the printing device 102 may verify the mechanical function of the printing device 102, the carriage 104, and/or the mechanical components that move the carriage 104 based on receiving a response matching the expected response. Alternatively, if the response does not match the expected response, then the settings (e.g., speed, power, timing, etc.) of the printing device 102, the carriage 104, and/or the mechanical components that move the carriage 104 may be calibrated until the expected response is received. Further, if the response does not match the expected response, then an error or mechanical failure may be reported by the printing device 102.

[0051] Referring back to the earlier described examples including a plurality of emitters on the printing device 102, alignment and optical data transmission between the plurality of emitters and the photo detector 116 of the fluid ejection device 106 may be utilized to verify mechanical function. For example, where the photoemitters may be located at the two opposing extremes of the length of travel of the printer carriage 104 in the carriageway 110, successfully optical data transmission at the photoemitters at the two opposing extremes of the length of travel may verify that the printer carriage 104 is achieving its expected full range of motion.

[0052] Further, where the photoemitters are spaced at specific intervals along the carriageway 110 the timing of the successful optical data transmission from each of the photoemitters may verify the timing and/or speed of the printer carriage 104 as it sweeps across the carriageway 110 is consistent with the expected timing and/or speed of the printer carriage 104. Furthermore, a plurality of photoemitters located along the carriageway 110 may be utilized to detect angular misalignments of the printer carriage 104 based on successful or unsuccessful optical data transmission across the plurality of photoemitters.

[0053] FIG. 2 is a diagram of an example optical data transmission fluid ejection device 206 according to the present disclosure. The described components and/or operations of the fluid ejection device 206 may include and/or be interchanged with the described components and/or operations described in relation to FIG. 1 and FIG, 3 - FIG. 6.

[0054] The fluid ejection device 206 may include and/or be a printing substance reservoir. In some examples, the fluid ejection device 206 may include a pen body (e.g., an inkjet pen body) and a fluidic die 215. The fluidic die 215 may include including electronic components (e.g., wire traces, bond pads, etc.), such as to provide an electrical connection to other components of the fluid ejection device 206. The fluidic die 215 may include a printing substance ejector and/or fluid actuator to eject the printing substance from the fluid ejection device 206 onto a printing medium. The fluid ejection device 206 may include nozzles through which printing substance may be ejected onto a printing medium. The nozzles may be integrated in and/or positioned over the fluidic die 215.

[0055] The fluid ejection device 206 may be a consumable reservoir of a printing substance that may be utilized in a printing device to execute printing operations including transferring the printing substance from the fluid ejection device 206 to a printing medium. The fluid ejection device 206 may be a component which may be connected to a printing device to execute printing operations and which may be removed from the printing device and replaced when it is exhausted.

[0056] The fluid ejection device 206 may include a photodetector 216. The photodetector 216 may include a component that detects electromagnetic radiation incident upon it. For example, the photodetector 216 may include a photodiode semiconductor and/or a phototransistor. In some examples, the photodetector 216 may include a phototransistor and/or photodiode semiconductor (e.g., complementary metal-oxide-semiconductor (CMOS)) which responds to electromagnetic radiation, such as light, incident upon it by generating and/or amplifying an electric current. For example, the photodetector 216 may include a Negative-Positive-Negative (NPN) type phototransistor. In some examples, the NPN phototransistor may include a photodiode at its base-collector junction. The NPN transistor may include electron-hole pairs photogenerated in the junction regions. In some examples, including N1PN2 phototransistors, electromagnetic radiation striking the photodetector 216 may cause electrons at collector junctions of the photodetector 216 to flow from a p-base to an N2 collector and be replenished from the Ni emitter to the base through an emitter junction resulting in photoconduction and/or the generation or modulation of an electrical current.

[0057] The photodetector 216 may be sensitive to (e.g., able to detect and/or respond to) a select subset of the electromagnetic spectrum. For example, the photodetector 216 may be sensitive to a select subset of electromagnetic radiation wave frequencies and/or wavelengths.

[0058] In some examples, the photodetector 216 may be sensitive to a select subset of electromagnetic radiation wave frequencies and/or wavelengths based on a depth of the photoconductive portion of the photodetector 216 within a substrate. For example, a collector junction of an NPN phototransistor may be implanted at a first depth within a silicon substrate such that a particular first subset of electromagnetic radiation having first wave frequencies and/or wavelengths may reach the junction and activate the photodetector 216 while others may not. Alternatively, a collector junction of an NPN phototransistor may be implanted at a second depth within a silicon substrate such that a particular second subset of electromagnetic radiation having second wave frequencies and/or wavelengths may reach the junction and activate the photodetector 216 while others may not.

[0059] In some examples, the photodetector 216 may be sensitive to a subset of electromagnetic radiation wave frequencies and/or wavelengths based on an electromagnetic radiation filter applied to the photodetector 216. For example, the fluid ejection device 206 may include an electromagnetic radiation filter to prevent electromagnetic radiation outside a specific portion of an electromagnetic spectrum from detection by the photodetector 216. For example, an electromagnetic radiation filter that filters out a portion of the electromagnetic spectrum may be placed over a photodetection portion of the photodetector 216. For example, a filter may be placed over the photodetector 216 that prevents a portion of the electromagnetic spectrum from reaching and/or being incident upon the photodetector 216. As such, the particular subset of electromagnetic radiation wave frequencies and/or wavelengths that a photodetector 216 is sensitive to may be determined by the wave frequencies and/or the wavelengths of the electromagnetic radiation that the electromagnetic radiation filter permits or blocks transmission of.

[0060] The photodetector 216 may be placed at any of a plurality of locations on the fluid ejection device 206. The location of the photodetector 216 may be selected such that the photodetector 216 may align with a photoemitter of a printing device while the fluid ejection device 206 is utilized in the printing device. For example, the location of the photodetector 216 may be selected such that while the fluid ejection device 206 is engaged within a printer carriage and moved, by moving the carriage, to a first position along the carriageway, the photodetector 216 may approximately align with a position of a photoemitter on the printing device. The location of the photodetector 216 may be selected such that it is oriented to detect electromagnetic radiation in the carriageway that was directionally emitted from a photoemitter. As such, the photodetector 216 may be located on a surface of the fluid ejection device 206 where it has a clear detection path into the carriageway. [0061] The photodetector 216 may be located on a die on the fluid ejection device 206. In some examples, the photodetector 216 may be located on the fluidic die 215. For example, as illustrated, the photodetector 216 may be located on the same fluidic die 215 that includes the printing substance ejector and/or fluid actuators to eject the printing substance from the fluid ejection device 206 onto a printing medium. Alternatively, the photodetector 216 may be located on a die on the fluid ejection device 206 that is distinct from the fluidic die 215.

[0062] In some examples, the photodetector 216 may be located at one of a plurality of distinct locations of on the fluid ejection device 206. Each location of the plurality of distinct locations may correspond to a distinct identity of an attribute of the fluid ejection device 206. As such, the location of the photodetector 216 on the fluid ejection device 206 may be indicative of the identity of an attribute or type of the fluid ejection device 206. For example, the location of the photodetector 216 on the fluid ejection device 206 may be indicative of an attribute or type of the fluid ejection device 206 that may be utilized to verify a manufacturer, a printing substance type, a compatibility with a printing device, a commercial designation, etc.

[0063] For example, the location of the photodetector 216 on the fluid ejection device 206 may indicate a manufacturer type of the fluid ejection device 206. For example, a first manufacturer identity may be indicated by the photodetector 216 being located at a first location on the fluid ejection device 206 and a second manufacturer identity may be indicated by the photodetector 216 being located at a second location on the fluid ejection device 206.

[0064] In another example, the location of the photodetector 216 on the fluid ejection device 206 may indicate a printing substance type contained in the fluid ejection device 206. For example, a first type (e.g., color, formulation, chemical makeup, etc.) of printing substance may be indicated by the photodetector 216 being located at a first location on the fluid ejection device 206 and a second type of printing substance may be indicated by the photodetector 216 being located at a second location on the fluid ejection device 206.

[0065] In another example, the location of the photodetector 216 on the fluid ejection device 206 may indicate a compatibility type of the fluid ejection device 206. For example, a first compatibility type (e.g., type of printing device that the fluid ejection device may be used with, etc.) of the fluid ejection device 206 may be indicated by the photodetector 216 being located at a first location on the fluid ejection device 206 and a second type the fluid ejection device 206 may be indicated by the photodetector 216 being located at a second location on the fluid ejection device 206.

[0066] In yet another example, the location of the photodetector 216 on the fluid ejection device 206 may indicate a commercial designation type of the fluid ejection device 206. A commercial designation type may refer to a designation such as a geographic area where the fluid ejection device 206 is designated to be sold, a consumer type (home consumer, small business consumer, corporate consumer, etc.) to whom the fluid ejection device 206 is designated to be sold, a designated device type (e.g., home consumer printer, small business consumer printer, corporate consumer printer, etc.), etc.

[0067] In some examples, fluid ejection device 206 and/or printing device manufacturers may sell fluid ejection devices 206 under commercial designations such as a subscription designation and a trade designation. A subscription designated fluid ejection device 206 may include a fluid ejection device that is provided by the fluid ejection device 206 manufacturer and/or printing device manufacturers as part of a subscription service where a customer pays a periodic fee and is provided fluid ejection devices 206 on a keep full basis. Such subscription designated fluid ejection devices 206 may be designated for use in printing devices associated with an active subscription. Alternatively, the trade designated fluid ejection device 206 may include a fluid ejection device 206 that is the generally commercially available version of the fluid ejection device 206 that can be acquired without a subscription and/or utilized in a printing device with or without an active subscription. In such examples, a first commercial designation type (e.g., trade, subscription, etc.) of the fluid ejection device 206 may be indicated by the photodetector 216 being located at a first location on the fluid ejection device 206 and a second commercial designation type of the fluid ejection device 206 may be indicated by the photodetector 216 being located at a second location on the fluid ejection device 206.

[0068] As described above, upon alignment between the photodetector 216 and a photoemitter of a printing device, the electromagnetic radiation directionally emitted from the photoemitter of the printing device may be detected by the photodetector 216 and converted to electrical current and/or digital data. As also described above, the photoemitter of the printing device may encode data in its electromagnetic radiation emissions. As such, the photodetector 216 of the fluid ejection device 206 may receive, upon alignment between the photodetector 216 and a photoemitter of the printing device, optically transmitted data encoded as electromagnetic radiation emitted from the photoemitter.

[0069] The fluid ejection device 206 may include a storage medium. The storage medium may include a non-transitory machine-readable memory to store data at the fluid ejection device 206. For example, the storage medium may be a storage location where the optically transmitted data encoded in the electromagnetic radiation and emitted from an aligned photoemitter may be stored.

[0070] In some examples, the storage medium may include a silicon state machine and/or shift register to observe and/or store a state. For example, each pulse of electromagnetic radiation emitted from a photoemitter of a printing device detected by an aligned photodetector 216 may advance a state of the silicon state machine. The state of the silicon state machine may, therefore, reflect and/or identify the optically transmitted data encoded in the electromagnetic radiation emitted from the photoemitter.

[0071] The optically transmitted data may be stored in the storage medium in the form of data queryable by a printing device. For example, a printing device may query an attached fluid ejection device 206 and/or its associated storage medium regarding the optically transmitted data stored thereupon. In an example, the printing device may query the data in the storage medium over a control line physically coupled to the fluid ejection device 206.

[0072] The fluid ejection device 206 may respond to the query with an indication of the data stored in the storage medium. The data indicated in the response may be compared to the data encoded in the electromagnetic radiation emitted from a photoemitter of a printing device. If the data in the response matches or otherwise confirms the identity of the data encoded in the electromagnetic radiation emitted from a photoemitter of a printing device, then it may be determined by the printing device that the optical data transmission between the fluid ejection device 206 and the printing device was successful. Alternatively, if the data in the response does not match or otherwise confirm the data encoded in the electromagnetic radiation emitted from a photoemitter of a printing device, then it may be determined by the printing device that the optical data transmission between the fluid ejection device 206 and the printing device was unsuccessful.

[0073] FIG. 3 is a diagram of an example optical data transmission printing device 302 according to the present disclosure. The described components and/or operations of the printing device 302 may include and/or be interchanged with the described components and/or operations described in relation to FIG. 1- FIG. 2 and FIG. 4A - FIG. 6.

[0074] The printing device 302 may include a carriage 304. The carriage 304 may be moveable within a carriageway 310. For example, the printing device 302 may include motors and/or other components to move the carriage 304 to a plurality of positions within the carriageway 310. In some examples, the carriage 304 may be moved along a carriage guide rail 312 to a plurality of positions within the carriageway 310.

[0075] The plurality of positions may include a plurality of positions along a print media feed path 322 (e.g., coming out of the page). The print media feed path 322 may include a path traversed by print media as the printing device 302 prints on it. For example, print media may be fed through the carriageway 310 and underneath the carriage 304 as printing substance is transferred from a fluid ejection device, engaged with and carried by the carriage 304, to the print media. In some examples, the carriage 304 may be moveable within the carriageway 310 along a path that is perpendicular to the media feed path 322. The carriage 304 may be moveable within the carriageway 310 to a plurality of positions along a print media feed path 322 such that the fluid ejection device, engaged with and carried by the carriage 304, can scan over the entire printable surface of the print media to deposit printing substance and form an image thereon.

[0076] The carriage 304 may include an ejection device engaging portion.

The ejection device engaging portion may be to attach a fluid ejection device to the carriage 304 where it may be retained during movement. The ejection device engaging portion may include a portion of the carriage 304 that is dimensioned to engage with and/or hold a fluid ejection device in engagement with the carriage 304 as it is moved. In some examples, the ejection device engaging portion may include a portion having a complementary geometry to compatible fluid ejection devices such that the fluid ejection devices may be press fit and retained in the carriage 304 while it is moved. In some examples, the ejection device engaging portion may include a fastener to fasten fluid ejection devices to and/or retained fluid ejection devices within the carriage 304 while it is moved.

[0077] The carriage 304 may include a physical data communication interface. The data communication interface may include wires, pins, electrical contacts, etc. that act as a communication interface for communication across the control line 308. For example, the data communication interface may include wires, pins, electrical contacts, etc. physically coupled with the control line 308 and/or the printing device 302. The data communication interface may include wires, pins, electrical contacts, etc. at the carriage 304 that may physically interface with wires, pins, electrical contacts, etc. on an installed fluid ejection device in order to communicatively couple the fluid ejection device and the printing device 302 via the control line 308 while the fluid ejection device is installed in the carriage 304.

[0078] The printing device 302 may include a photoemitter 314. The photoemitter 314 may be oriented on the printing device 302 such that it may emit electromagnetic radiation into a portion of the carriageway 310. The photoemitter 314 may emit electromagnetic radiation in a specific and directional manner such that the emitted electromagnetic radiation is detectable by aligned (e.g., opposingly oriented across the print media feed path 322) photodetectors, but not detectable by unaligned photodetectors. As such, the portion of the carriageway 310 where the electromagnetic radiation is emitted may be limited to projecting into an area of the carriageway 310 that is immediately adjacent to the photoemitter 314. [0079] The printing device 302 may include a processor and non-transitory machine-readable storage medium to store instructions executable by the processor. In some examples, the processor and/or the non-transitory machine-readable storage medium to store instructions executable by the processor may include a printing device 302 controller.

[0080] The instructions may be executable by the processor to cause the photoemitter 314 to encode data into its electromagnetic radiation emissions. For example, the photoemitter 314 may translate data, such as an identification (e.g., a pen identification, a command address, etc.) to be assigned to an attached fluid ejection device, into modulations to its electromagnetic radiation emissions. The photoemitter 314 may then optically transmit the data, encoded in its electromagnetic radiation emissions, into the portion of the carriageway 310 corresponding to the photoemitter’s 314 electromagnetic radiation emission field.

[0081] The instructions may be executable to query a fluid ejection device, to be attached to the carriage 304, about the optically transmitted data. As described above, the printing device 302 may include a control line to communicatively connect the printing device 302 to a to be connected fluid ejection device to enable the processer to query the to be attached fluid ejection device. In some examples, the processor may query an attached fluid ejection device about the optically transmitted data across the control line 308.

[0082] The printing device 302 may receive a response to its query about the optically transmitted data from the attached fluid ejection device. The printing device 302 may analyze such responses to determine whether the response is indicative of a successful optical transmission of data from the photoemitter 314 of the printing device 302 to the photodetector of an attached fluid ejection device. For example, the printing device 302 may include comparing the data received in the response to the data that was sent via the photoemitter 314. If the data is a match, then a determination may be made that the photoemitter 314 of the printing device 302 achieved alignment with the photodetector of an attached fluid ejection device at the correct time corresponding to the time of the electromagnetic radiation emission. As such, a determination may be made that the optical transmission of data from the photoemitter 314 of the printing device 302 to the photodetector of an attached fluid ejection device was successful. [0083] In some examples, the printing device 302 may include instructions executable by the processor to verify a mechanical function of the carriage 304. The mechanical function of the carriage 304 may be verified based on a response to the query to the to be attached fluid ejection device. As described above, if analysis of the data included in a response matches the data encoded in the electromagnetic radiation emissions of the photoemitter 314, then it may be determined that the photoemitter 314 of the printing device 302 achieved alignment with the photodetector of an attached fluid ejection device at the correct time corresponding to the time of the electromagnetic radiation emission. It may be inferred from this determination that the mechanical function of the carriage 304 and/or the components that move the carriage 304 is performing as expected in order to produce the timely alignment. As such, the successful optical data transmission between the printing device 302 and an attached fluid ejection device may serve as a verification of the correct mechanical function of the fluid ejection device. As mentioned above, a plurality of photoemitters located on the printing device 302 may be utilized. The successful optical data transmission between the printing device 302 via the plurality of photoemitters and an attached fluid ejection device may serve as a verification of the correct mechanical function of the fluid ejection device.

[0084] In some examples, the printing device 302 may include instructions executable by the processor to verify a type of the fluid ejection device to be attached to the printer carriage 304. The type of fluid ejection device may be verified based on a response to a query to the to be attached fluid ejection device. As described above, if analysis of the data included in a response matches the data encoded in the electromagnetic radiation emissions of the photoemitter 314, then it may be determined that the photoemitter 314 of the printing device 302 achieved alignment with the photodetector of an attached fluid ejection device at the correct time corresponding to the time of the electromagnetic radiation emission. As described above, the location of a photodetector on fluid ejection device may be indicative of type of that ejection device. As such, if the carriage 304 is moved to a first position that is expected to produce an alignment between the photoemitter 314 and a photodetector at a first location on a fluid ejection device that would be indicative of the fluid ejection device being of a first type, then a determination of a successful alignment based on the query response would verify that the fluid ejection device is of the first type. In some examples, the carriage 304 may be moved to another position corresponding to another photodetector location on the fluid ejection device that is indicative of the fluid ejection device being of a second type.

[0085] FIG. 4A - FIG. 4C are sequential diagrams of an example optical data transmission printing device 402 verifying a type of a fluid ejection device 406 according to the present disclosure. The described components and/or operations of the printing device 402 and/or a fluid ejection device 406 may include and/or be interchanged with the described components and/or operations described in relation to FIG. 1- FIG. 3 and FIG. 5 - FIG. 6.

[ooeq FIG. 4A illustrates a printing device 402 with a printing carriage 404 located at a first position within a carriageway 410. The printing carriage 404 may be moveable within the carriageway 410 along a carriage guide rail 412.

[0087] The printing device 402 may include a photoemitter 414. The photoemitter 414 may be oriented to emit electromagnetic radiation into the carriageway 410. The photoemitter 414 may optically transmit data, encoded as electromagnetic radiation emissions, into a portion of the carriageway 410.

[0088] A fluid ejection device 406 is illustrated removably attached to the carriage 404. The fluid ejection device 406 may be moved within the carriageway 410 along with the carriage 404. The fluid ejection device 406 may include a photodetector 416. The photodetector 416 may detect electromagnetic radiation incident upon its collection junctions and covert the radiation to an electrical current and/or to digital data. As such, the photoemitter 414 and the photodetector 416 may form a wireless optical data transmission path between the printing device 402 and the fluid ejection device 406.

[0089] The fluid ejection device 406 may include a storage medium. The storage medium may be utilized to store data at the fluid ejection device 406. For example, the data encoded as electromagnetic radiation that was optically transmitted from the photoemitter 414 to the photodetector 416 may be saved to the storage medium. For example, the storage medium of the fluid ejection device 406 may be utilized as a storage location for data interpreted from the electromagnetic radiation emissions received at the photodetector 416.

[0090] The data stored at the storage medium may be queryable. For example, the printing device 402 may query the storage medium in order to determine whether the data stored thereupon corresponds to and/or matches the data sent as electromagnetic radiation emissions from the photoemitter 414. In some examples, the query may be submitted from the printing device 402 to the fluid ejection device 406 via a control line 408 connection between the printing device 402 and the fluid ejection device 406.

[0091] A response to the query may be submitted by the fluid ejection device 406 across the control line 408. For example, the printing device 402 may receive a response to the query from the fluid ejection device 406 across the control line 408. The printing device 402 may analyze the response. If the analysis by the printing device 402 of the query response from the fluid ejection device 406 indicates that the data stored in the storage medium matches the data encoded in the electromagnetic radiation emissions of the photoemitter 414, then it may be determined that the photoemitter 414 of the printing device 402 achieved alignment with the photodetector 416 of an attached fluid ejection device 406 at the correct time corresponding to the time of the electromagnetic radiation emission.

[0092] FIG. 4B illustrates the printing device 402 with the printing carriage 404 located at a second position within the carriageway 410. In the second position, the printer carriage 404 may be in a position that is known to align the photoemitter 414 with a photodetector at a first location on a fluid ejection device 406. The presence of the photodetector at the first location on the fluid ejection device 406 may indicate that the fluid ejection device 406 is of a first type (e.g., subscription type).

[0093] As the printing carriage 404 reaches the second position, the photoemitter 414 may be caused to optically transmit data encoded as electromagnetic radiation emissions into the carriageway 410. However, as illustrated, the fluid ejection device 406 does not have the photodetector at the first location on the fluid ejection device 406. As such, the transmission of data encoded as electromagnetic radiation emissions from the photoemitter 414 will not be received by the fluid ejection device 406.

[0094] The printing device 402, not knowing if the transmission of data encoded as electromagnetic radiation emissions from the photoemitter 414 was received by the fluid ejection device 406, may query a storage location of the fluid ejection device about the data encoded as electromagnetic radiation emissions from the photoemitter 414. The storage medium may be queried over the control line 408. Based on a response, or lack thereof, to the query the printing device may determine that the fluid ejection device 406 did not receive the data encoded as electromagnetic radiation emissions from the photoemitter 414. As such, the printing device 402 may determine that the fluid ejection device 406 is not an ejection device of the first type since the positioning of the carriage at the second location (corresponding to an alignment with a photodetector on a fluid ejection device of the first type) did not result in a verifiable alignment between the photoemitter 414 and a photodetector 416 on the fluid ejection device 406.

[0095] FIG. 4C illustrates the printing device 402 with the printing carriage 404 located at a third position within the carriageway 410. The printing carriage 404 may be moved to the third position within the carriageway 410 responsive to a determination by the printing device 402, based on the response to its query from the fluid ejection device 406, that an optical data transmission attempt in the second did not result in a verifiable alignment between the photoemitter 414 and a photodetector 416 on the fluid ejection device. In the third position, the printer carriage 404 may be in a position that is known to align the photoemitter 414 with a photodetector 416 at a second location on a fluid ejection device 406. The presence of the photodetector 416 at the second location on the fluid ejection device 406 may indicate that the fluid ejection device 406 is of a second type (e.g., trade type).

[0096] As the printing carriage 404 reaches the third position, the photoemitter 414 may be caused to optically transmit data encoded as electromagnetic radiation emissions into the carriageway 410. As illustrated, the fluid ejection device 406 has the photodetector 416 located at the second location on the fluid ejection device 406. As such, the transmission of data encoded as electromagnetic radiation emissions from the photoemitter 414 is received by the photodetector 416 of fluid ejection device 406 and/or is saved to the storage medium.

[0097] The printing device 402, not knowing if the transmission of data encoded as electromagnetic radiation emissions from the photoemitter 414 was received by the fluid ejection device 406, may query the storage medium of the fluid ejection device 406 about the data emitted from the photoemitter 414. The storage medium may be queried over the control line 408. Based on a response to the query, the printing device 402 may determine that the fluid ejection device 406 received the data encoded as electromagnetic radiation emissions from the photoemitter 414. For example, the data reported in the response may match the data emitted by the photoemitter 414. As such, the printing device 402 may determine that the fluid ejection device 406 is an ejection device of the second type since the positioning of the carriage at the third location (corresponding to an alignment with a photodetector 416 on a fluid ejection device 406 of the second type) did result in a verifiable alignment between the photoemitter 414 and a photodetector 416 on the fluid ejection device 406.

[0098] FIG. 5 is a diagram of an example optical data transmission printing device 502 according to the present disclosure. The described components and/or operations of the printing device 502 may include and/or be interchanged with the described components and/or operations described in relation to FIG. 1- FIG. 4C and FIG. 6.

[0099] The printing device 502 may include a processor 540 and/or a non- transitory memory 542. The non-transitory memory 542 may include instructions (e.g., 544, 546, etc.) that, while executed by the processor 540, cause the printing device 502 to perform various operations described herein.

[00100] The printing device 502 may include instructions 544 executable by the processor 540 to cause a photoemitter to optically transmit data, encoded as electromagnetic radiation emissions, into a portion of the carriageway. The data may include a pen identification to be assigned to the removeable fluid ejection device.

[00101] The carriageway may contain a carriage moveable within the carriageway to a plurality of positions. The carriage may include a fluid ejection device engaging portion to attach a fluid ejection device to the carriage.

[00102] The printing device 502 may include instructions 546 executable by the processor 540 to query a fluid ejection device, to be attached to the carriage, about the optically transmitted data. For example, the printing device 502 may include a control line to communicatively connect the printing device 502 to the to be attached fluid ejection device. The control line may be utilized by the processor 540 to query the to be attached fluid ejection device regarding the optically transmitted data.

[00103] The printing device may also include instructions executable by the processor 540 to verify, in response to a query to the to be attached fluid ejection device, a mechanical function of the carriage. Additionally, the printing device may include instructions executable by the processor 540 to verify, in response to a query to the to be attached fluid ejection device, a type of fluid ejection device to be attached.

[00104] Verifying the mechanical function of the carriage may include verifying that the carriage is moving within an expected range of motion. This may be achieved by validating alignment between photodetectors and/or photoemitters at opposing extremes of an expected range of motion for the carriage by verifying an optical data transmission between those photodetectors and/or photoemitters based on a query response.

[00105] Verifying the mechanical function may include verifying the speed and/or timing of the carriage movement. This may be achieved by validating alignment between photodetectors and/or photoemitters at spaced intervals by verifying an optical data transmission between those photodetectors and/or photoemitters at expected time intervals based on a query response.

[00106] Verifying the mechanical function may include verifying the angular alignment of the carriage within the carriageway. This may be achieved by validating alignment between photodetectors and/or photoemitters at spaced intervals by verifying an optical data transmission between those photodetectors and/or photoemitters based on a query response. For example, a printing device 502 may include a plurality of photoemitters at spaced apart distances on the printing device 502. The fluid ejection device may include a plurality of photodetectors at correspondingly spaces apart distances on the fluid ejection device. The simultaneous alignment between the plurality of photoemitters and the plurality of photodetectors, as verified by simultaneous successful optical data transmission verified based on a query response, may indicate an expected angular alignment of the fluid ejection device and/or the carriage.

[00107] FIG. 6 is a diagram of an example optical data transmission method 650 according to the present disclosure. The described components and/or operations of the method 650 may include and/or be interchanged with the described components and/or operations described in relation to FIG. 1- FIG. 5.

[00108] At 652, the method 650 may include moving a carriage of a printing device. Moving the carriage of the printing device may include driving a stepper motor to advance the carriage through the carriage way. The carriage of the printing device may be moved to a first position within the carriageway.

[00109] At 654, the method 650 may include causing a photoemitter of the printing device to perform an optical data transmission. Performing an optical data transmission may include transmitting data as electromagnetic radiation emissions into a portion of the carriageway. [00110] Performing the optical data transmissions may include encoding the data as electromagnetic radiation emissions. In some examples, the data may be encoded as bits of data expressed through modulations of the electromagnetic radiation emitted by a photoemitter of the printing device.

[00111] For example, transmitting the data as electromagnetic radiation emissions may include modulating an identity of a bit of the data during the optical transmission by modulating a periodicity of the electromagnetic radiation emissions from the photoemitters. In some examples, transmitting the data as electromagnetic radiation emissions may include modulating an identity of a bit of the data during the optical transmission by modulating a wave frequency of the electromagnetic radiation emissions from the photoemitter.

[00112] In some examples, a photodetector on a fluid ejection device attached to the carriage may detect the electromagnetic radiation emissions from the photoemitter. The fluid ejection device may save the data encoded in the electromagnetic radiation emissions to a storage medium associated with the fluid ejection device. The data may be saved as queryable data. For example, the data may be made available to be queried by the printing device over a control line that is separate from the optical data transmission link establish between the photoemitter of the printing device and the photodetector of the fluid ejection device.

[00113] At 656, the method 650 may include querying a fluid ejection device, to be attached to the carriage, about the optically transmitted data. For example, the fluid ejection device may query the data saved to the memory location of the fluid ejection device. The printing device may query the data over the control line linking the printing device and the fluid ejection device. Querying the data may include requesting the fluid ejection device to reproduce the data it received via the optical data transmission link to the printing device. The data may then be compared to the data that was sent from the printing device to the fluid ejection device to determine whether the data matches.

[00114] If the two match each other, the printing device may determine that the optically transmitted data was received by the fluid ejection device. If the two do not match or if no response to the query is received, then the printing device may determine that the optically transmitted data was not received by the fluid ejection device. [00115] In some examples, the method 650 may include moving, responsive to a determination that the optically transmitted data was not received by the fluid ejection device to be attached to the carriage, the carriage of the printing device to a second position along the carriageway. In response, the photoemitter of the printing device may be caused to perform a second optical transmission of the data into the portion of the carriageway. Following the second optical transmission of the data, a type of the fluid ejection device to be attached to the carriage may be determined based on a determination that the fluid ejection device to be attached to the carriage received the second optical transmission of the data.

[00116] In some examples, the method 650 may include causing the photoemitter of the printing device to perform the optical transmission of the data as electromagnetic radiation emissions with a first wave frequency. The first wave frequency may be a wave frequency detectable by a photodetector on a fluid ejection device of a first type. Responsive to a determination that the optically transmitted data was not received by the fluid ejection device to be attached to the carriage, the photoemitter of the printing device may be caused to perform a second optical transmission of the data. The second optical transmission of the data may include the optical transmission of the data as electromagnetic radiation emissions with a second wave frequency. The second wave frequency may be a wave frequency detectable by a photodetector on a fluid ejection device of a second type. Following the second optical transmission of the data, a type of the fluid ejection device to be attached to the carriage may be determined based on a determination that the fluid ejection device to be attached to the carriage received the second optical transmission of the data.

[00117] In the foregoing detailed description of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration how examples of the disclosure may be practiced. These examples are described in sufficient detail to enable those of ordinary skill in the art to practice the examples of this disclosure, and it is to be understood that other examples may be utilized and that process, electrical, and/or structural changes may be made without departing from the scope of the present disclosure. Further, as used herein, "a plurality of” an element and/or feature can refer to more than one of such elements and/or features.