In addition to this, the invention relates to a circuit which may be used for individually controlling the bulbs of a light string independently of other bulbs of the string. The strings will be applicable for decoration of anything from X-mas trees, electric news- papers, shops, discotheques, etc. In theory, the light string may consist of an indefi- nite number of bulbs, all of which may be turned on and off individually.

Prior art.

Light strings of this type, also called light scanners, are based on wires being drawn to each single bulb of the string. The bulbs are connected in groups so that for in- stance each third or fourth bulb of the string turns on or off simultaneously. This so- lution requires a very large number of wires if it is desired to control many bulbs of a string.

Systems for controlling switches in a string of light emitters are known from the prior art. Normally a wire for controlling the light emitters is connected to each single light emitter or to a group of light emitters, which can the be controlled as group but not individually. The drawbacks of such prior systems is that very extensive wiring is required when the number of light emitters increases.

Systems for controlling multiple lights on a light string are known from the prior art.

WO 94/18809 (PHARES) concerns a controlled lighting system comprising a control system, a plurality of light modules, each module including at least two light ele- ments, a control unit for each light module receiving control signals from the control system and independently operating each of the two light elements in response to

the control signals, each control unit operating in response to a unique control sig- nal. Thus the individual lights are reached by the control system by sending a signal containing the unique address of the light module in question.

A similar system is known from WO 99/12400 (DE LEIJER). The disclosure con- cerns a display system comprising a number of light emitters and a central control unit. Each light emitter is mounted in a holder having a local control unit. The local control unit has a writable memory, in which an address assigned to the local control unit is stored. The central control unit accesses the local control unit by transmitting a message containing the address for activating the light emitter. The light emitters are in principle all similar but they are programmed by the central control unit, which assigns each and every local control unit a unique address.

US 5,315,160 (CHANG) concerns a sequentially shifting control circuit for extendible light strings, which includes a main controller in one end, a backward signal- generating circuit in the other end and a plurality of bi-directional shifting control units therebetween. The light string can do forward or backward shifting in respec- tive ends thereof or even do bi-directional shifting simultaneously.

A general disadvantage of the prior systems is that the light emitters either need to be manufactured individually, which is incompatible with modern industrial tech- niques, or that the memory of each single light unit needs to be programmed before operating the system. Each signal then has to comprise the address of the light emitter to be controlled and the data signal to be transmitted to the individual light emitter causing it to switch on or off. Thus large amounts of data have to be trans- mitted to control the prior string of switch units.

It is the purpose of the present invention to provide a simple system for controlling a multiplicity of switch units in which all switch units may be identical, and which does not require extensive wiring.

Summary of the invention.

According to a first aspect of the invention there is provided a method for controlling individual switches in a string comprising the steps of

i) transmitting a clock signal from a central control unit to a switch unit, ii) transmitting a data signal information from a central control unit to a switch unit, iii) transmitting the data signal information and the clock signal from a first switch unit to the next switch unit at each clock signal, iv) repeating steps i) to iii) a number of times corresponding to a pre-determined number of switches in a series, v) transmitting a latch signal information latching the data into the driver of each switch unit, vi) switching the switch units on or off corresponding to the received signals.

The advantage of the present invention is that all switch units on the string are iden- tical and thus can be manufactured rationally by an industrial process. Similarly there is no need for programming a memory of each switch unit prior to controlling the units. A further advantage is that simple wiring can be used to transmit the con- trolling signals to the switch units.

Preferably, step iv) is repeated a number of times corresponding to the number of switch units in the string.

According to one embodiment of the invention, it is possible to control a complete string of switches by having only one signal wire connecting the switch units. This provides especially simple wiring. In order to transmit several types of signal infor- mation via the same wire the data signal information and/or the latch signal informa- tion may be transmitted as changes in clock frequency.

The wire may be replaced by wireless transmission from the central control unit to the first switch unit in the string. This may be convenient for certain applications.

The switch units may be connected in parallel to a power supply. Thereby, espe- cially simple control of the string of switch units is obtained, since the single units can be switched on and off without affecting the power supply to the other switch units. The string of switch units may comprise two or more power supplies to com- pensate for the drop in voltage as the length of the string is increased, or each

switch unit may have its own power supply if they require different voltage or a high voltage.

Preferably the power supplied to the switch units is direct current. Any kind of volt- age may be used depending on the power requirement of the devices connected to the switch units. In the case of light emitters a voltage of 1,3,9,12 volts or higher may be advantageous.

Advantageously one, two or more means to generate constant current may be com- prised in the string of switches. Thereby sub-series of serially connected switch units may be used to extend the length of the string of switch units.

Normally, the length of a string of serially connected electrical devices such as light emitters cannot exceed 3 to 4 meters. The drop in voltage due to the resistance of the wire is simply too great over larger distances. By providing constant current generators at intervals on the string and by leading the current around the switch unit, when the switch unit is off, the length of the string can be increased considera- bly. In principle the length can be indefinite and experiments have shown that the length can be increased at least by a factor of 5 to 6. String lengths exceeding 10 to 12 meters are easily reached.

The signals used to control the control circuits may be generated at any possible frequency. The choice of frequency depends on the use of the method. Thus the signal frequency may be in the range between 50 Hz and 1 kHz, such as 100,200, or 500 Hz or between 1 and 50 kHz, such as 2,4,5,10,15,20,25,30, or 40 kHz or even higher such as 100,200, or 500 kHz.

The switch units may switch light on and off. By making the control circuit of the light string form part of the light string (for example by incorporating it in the bulb or in a socket) one achieves the possibility of controlling all the bulbs of the light string indi- vidually by means of a very small number of wires without the need to draw a wire to each single link of the string.

According to other embodiments the switch units may control a valve or a relay.

Advantageously the signals are transmitted via a wire for at least part of the dis- tance, but if required at least one of the signals may be transmitted wirelessly at least part of the distance.

According to an especially preferred embodiment at least one of the data, clock or latch signals are amplified. The signals may be amplified at intervals in the string.

According to this embodiment, it becomes possible to extend the length of the string of control circuits.

According to another aspect of the invention there is provided a system for control- ling individual switches in a string comprising i) at least two switch units, ii) a central control unit capable of generating clock, data, and latch signals, iii) at least one power supply unit providing electrical power to the switch units, iv) transmitting means for transmitting a clock signal from the central control unit to a switch unit, v) transmitting means for transmitting a data signal information from the central control unit to a switch unit, vi) transmitting means for transmitting a latch signal information from the central control unit to the switch units, vii) transmitting means for transmitting a data signal information and a clock sig- nal from a first switch unit to the next switch unit, viii) and in each switch unit a control circuit.

Advantageously the control circuit of the system comprises means for detecting the clock signal, means for detecting the data signal, and means for detecting the latch signal. The control circuit may be provided as an integrated circuit.

Advantageously the control circuits are serially connected to one another. Thereby the full advantage of the simple wiring system can be used.

The switch units may be serially connected to the power supply means or connected in parallel to the power supply means.

Advantageously, the switch units are supplied with direct current. The current may be supplied from two or more power supply units to compensate for the drop in volt- age and thereby increase the length of the string or each switch unit may be con- nected to its own power supply if required.

In order to increase the length of the string the system may comprise one or plural means to generate constant current.

According to an especially preferred embodiment at least one of the transmitting means is a wire, but if required at least one of the means for transmitting signals from the central control unit to a first switch unit may be a wireless transmitting means.

In order to simplify the wiring, the transmitting means for transmitting the data, the clock and the latch signal could be one and the same means. Thereby only one wire is required to control the whole string of switches. As alternative embodiments, the transmitting means for transmitting the data and clock signal, or for transmitting the data and latch signal, or for transmitting the clock and latch signal may be one and the same means. Accordingly, the number of wires can be reduced to two wires instead of three wires.

The means for detecting the clock signal may comprise a counter and the means for detecting the data signal may comprise a counter and a timer. This embodiment is advantageous when the transmitting means for transmitting the clock signal and the data signal information is one and the same means. The means for receiving and transmitting the data signal in the switch units may comprise a flip-flop or a FET (field-effect transistor). At each clock signal the flip-flop will transmit the data from D to Q (see Fig. 2, Latch (3)) and thereby send the data on to the control circuit of the next switch unit in the string. Similarly the means for receiving the latch signal in the switch units may comprise a flip-flop or a FET (field-effect transistor).

The means for detecting the latch signal may comprise a timer or a time-recorder.

This is advantageous, when the latch signal information is transmitted via the same wire as the clock or the data signals.

The driver, which turns the electrical device controlled by the switch unit on or off may be a transistor or may be selected from the group consisting of a bipolar tran- sistor, a digital transistor, a power transistor, a Darlington transistor, a RF bipolar transistor, a unijunction transistor, an insulated gate bipolar transistor, a relay, an analogue switch, a FET (field-effect transistor) such as a MOSFET, a HEX FET, a junction FET, or a RF MOSFET.

The electrical devices controlled by the switch units may be light emitters, relays, valves, engines, hydraulic or pneumatic devices, or heating or cooling devices.

The central control unit used to control the string of control circuits may be a per- sonal computer. Advantageously, the program for controlling the string may be made in a computer and transferred into a device comprising a memory, means to generate a signal, a data input port, and a data-output port. This device may be more adapted to control the string of control circuits than a personal computer, since the central processing unit of a personal computer may be busy doing other things than controlling the circuits. The device may further comprise a processor and/or at least one further data-output port. Thus it is possible for the device to control one, two or more strings of control circuits at one time.

According to a third aspect of the invention there is provided a method for transmit- ting data from at least two detector units in a string to a central unit comprising the steps of i) detecting a signal in each detector unit, ii) transmitting a latch signal information from the central control unit to the at least two detector units latching the data from the detector unit into a data unit, iii) transmitting a clock signal from a central control unit to a detector unit, iv) transmitting a data signal information from a detector unit to the next detector unit at each clock signal, v) repeating steps iii) to iv) a number of times corresponding to a pre- determined number of detector units in the string.

According to this aspect of the invention, the general inventive principle of transmit- ting data between units on a string is used for collecting data rather than for

spreading data. This can also be done without extensive wiring and without every detector unit having a unique address. The units are simply identified by their num- ber in a string.

Preferred and advantageous embodiments of this aspect of the invention are the same as those of the aspect of controlling a string of switch units.

The detector units may detect movement, light, temperature, the open or closed condition of door, windows, drawers or the presence or voltage of a current in an electrical circuit. The signals transmitted to the central unit are of the on/off or 0/1 type, but more complex signals may be transmitted by transmitting a string of sig- nals from each detector unit. This is advantageously done by providing each detec- tor unit with several serially connected control circuits.

Detailed description of the invention.

The invention will now be described in further detail with reference to the drawings.

In the drawings, the system and method of the present invention have been illus- trated using bulbs. This is done solely for illustrative purposes. The bulb may be replaced with any kind of device, which can be switched on or off.

Fig. 1 shows a block diagram of a five-wire (Vcc, gnd, data, clock, and latch) control circuit for a light string.

Fig. 2 shows a block diagram of a four-wire (Vcc, gnd, data, and clock) control circuit for a light string.

Fig. 3 shows a block diagram of a three-wire (Vcc, gnd, data) control circuit for a light string.

Fig. 4 shows a schematic diagram of the signals transmitted in a system according to fig. 1.

Fig. 5 shows a schematic diagram of the signals transmitted in a system according to fig. 2.

Fig 6 shows a schematic diagram of the signals transmitted in a system according to fig. 3.

Fig. 7 shows a schematic block diagram, where a number of power supplies are inserted in parallel connection.

Fig. 8 shows a schematic block diagram, where constant current generators have been inserted into the string of light emitters.

As will be evident from the description below, the control circuit for the switch units may be laid out basically in three different ways (in the case of light string): Control circuit for a light string for controlling the individual bulbs of a light string comprising an"electronically controlled switch" (7), a counter (6), a"timer" (5) (time recorder), a latch (3), a"latch detector" (4) (time recorder), a further latch (2), and a "driver" (1). The control circuit for a light string according hereto, may be provided as an integrated circuit.

Control circuit for a light string according to the above embodiment, characterised in that the data detection circuit is left out and is replaced by a further wire used for data. The circuit consists of a latch (3), a"latch detector" (4) (time recorder), a fur- ther latch (2), and a"driver" (1). The control circuit for a light string according hereto, may be provided as an integrated circuit.

Control circuit for a light string according to the above embodiment, characterised in that the latch detection circuit is left out and is replaced by a further wire used for latch. The circuit consists of a latch (3), a further latch (2), and a"driver" (1). The control circuit for a light string according hereto, may be provided as an integrated circuit.

The system of the invention is first described with reference to Fig. 1, which shows a control circuit with only one wire for the control circuits between the switch units. In addition to the wire for the control circuit, the system comprises two wires for the power supply.

The control circuit of the light string from input to output consists of the following parts in sequence: an electronically controlled switch (7), a counter (6), a"timer" (5) (time recorder), a latch (3), a latch detector (4) (time recorder), a further latch (2) and finally a driver (1).

The circuit is brought to function by transmitting a flow of pulses to the circuit. By having two different period lengths between the positive pulses (see Fig. 1) it is pos- sible to determine whether the single links of the string should be turned on or off. A short period will for example be detected as"turn off'hile a longer period will be detected as"turn on". A (still) longer interval between the pulses will mean that the desired result will automatically be latched to the bulb.

If a longer period has passed without any data, the circuit will be reset by the latch detector (4) and the counter (6) will be set to 0, whereby the electronic switch (7) will be set so that new data will be transmitted to the timer (5).

The first arriving pulse will start the timer (5) and at the same time count the counter (6) one up.

If there is a short interval between the first and the second pulse, the timer will not time out, whereby the latch (3) being activated by the second pulse will latch a"turn off' (for example a"0"). If, however, there is a long interval between the pulses, the timer (5) will time out and a"turn on"will be latched (for example a"1").

When the second pulse has been received, the counter (6) will simultaneously be counted up. When both pulses have been received, the counter (6) will activate the electronic switch (7) so that subsequent data will be passed on to the following link of the string.

The next time a very long period without any receipt of data occurs, the latch detec- tor (4) will activate the last latch (2) latching the detected result to the driver (1). At the same time, the circuit will be reset again and will be ready to receive new data.

Signals corresponding to this embodiment are shown in Fig. 4 and in the lower part of Fig. 1.

The driver (1) may in its simplest form consist of a transistor being used for passing the current through the bulb.

It may be advantageous to have a synchronic circuit (see Fig. 2) with a separate data and clock input in order to decrease the sensitivity to noise (EMC).

The circuit will in sequence from input to output consist of a latch (3), a latch detec- tor (4) (time recorder), a further latch (2) and finally a driver (1).

The circuit functions in such a manner that for each clock there is also a data signal.

For each clock, the data signal will be latched (3) on to the following link of the string. This means that the first data being sent from the control unit will affect the last link of the string and the last data being sent will affect the first link of the string.

If there is a longer interval between the clock pulses, the latch detector (4) will acti- vate the last latch (2) and thereby pass data on to the driver (1).

One example of a series of data transmitted in a system according to Fig. 2 is shown in Fig. 5. The signals consist of data and clock signals. In the present exam- ple signals are transmitted to four switch units in a series. The first signal transmitted is shown to the left of the figure. The first signal comprises both a clock and a data signal, and these are transmitted to the first unit in the string. As the next signal is transmitted, the first signal is sent on to the second unit in the string. As four signals have been transmitted, the period between signals is increased and the latch de- tector units in the four switch units will latch the data into the driver causing the switches to be turned on or off. In the present example the first, second, and fourth switch unit will be set to"on"and the third will be set to"off". This is because the first signal sent from the control will end up in the last switch unit in the string. In the left part of the figure the signals corresponding to the next string of signals is shown.

Here the fourth switch unit will be set to"off", the third will be set to"on"and the sig- nals corresponding to the first and second switch units are not shown.

If a further control of the circuit is desired, this may be achieved by introducing a further wire (see Fig. 3) which is to be used for latching when the desired data are present. A circuit is thereby achieved which is not dependent on the pulse interval ratio, but which may be controlled at exactly the desired timing.

The circuit will in sequence from input to output consist of a latch (3), a further latch (2) and finally a driver (1).

The circuit functions in such a manner that for each clock there is also a data signal.

For each clock, the data signal will be latched (3) on to the following link of the string. This means that the first data being sent will affect the last link of the string and the last data being sent will affect the first link of the string.

When all data have been sent, the last latch (2) may be activated, whereby data are passed on to the driver (1).

One example of as series of signals corresponding to a system according to Fig. 3 is shown schematically in Fig. 6. There are three kinds of signals: a clock, a data, and a latch signal. The signals should be read from the left and correspond as above to a string with four switch units. At the first clock signal an"on"data signal is sent to the first switch unit in the string. At the second clock signal an"off'data signal is sent to the first switch unit and the first"on"signal is sent on to switch number 2 etc.

After a total of four clock signals a single latch signal is sent to all switch units and the data is latched into the driver of the units with the result that the first, second, and fourth switch units are turned on, and the third unit is switched off. The next series of signals are shown to the right of the figure and the result of this series is that the first and third switch units are switched on and the second and fourth are switched off.

The latch detector used according to the embodiment where a separate latch signal is transmitted could be a flip-flop or a FET (field-effect transistor). In the case, where no separate latch signal is transmitted, the latch signal information is transmitted as an increase in the period between clock and/or data signals. In this case the latch detector could be a timer, which is pre-set to a certain period length. Every time the control circuit receives a clock signal, the timer is turned on. If the next clock signal

is received before the time has run out, the timer is re-started. If the period between the clock signals exceeds the pre-set time on the timer, the time runs out and a sig- nal is sent to the latch unit, causing the data contained in it to be loaded into the driver. Another possibility is to have a time-recorder, which records the time be- tween clock signals. This provides exactly the same technical effect.

The driver (data detector) used for turning on and off the electrical device controlled by the control circuit could be selected from the group consisting of a bipolar tran- sistor, a digital transistor, a power transistor, a Darlington transistor, a RF bipolar transistor, a uni-junction transistor, an insulated gate bipolar transistor, a relay, an analogue switch, a FET (field-effect transistor) such as a MOSFET, a HEX FET, a junction FET, or a RF MOSFET.

Figure 7 shows how a number of power supplies can be inserted into a string of light emitters. In the case of two or more power supplies 8,8'in the string, these are connected in parallel to the light emitters 9,9', 9", and 9"'or whichever other type of electrical device the switch units are to control. As the length of the chain is in- creased, the voltage drops and a second power supply 8'can be inserted. In this way, the length of the string of light emitters can be increased in principle indefi- nitely. The control circuits, which turn the light emitters on and off are all serially connected to each other independently of the power supply.

Another way of extending the length of the string of light emitters is shown sche- matically in figure 8. Here the current is supplied by a power supply 8 shown to the left of the figure. The power supply is connected to ground and in parallel to a num- ber of constant current generators 10,10'. Each of the constant current generators 10,10'supply a sub-string of serially connected light emitters with current. In order to be able to control the light emitters individually, the current is lead around the light emitters via a switch 11. For clarity, only one switch 11 is shown, but it is to be un- derstood, that each of the light emitters 9,9', 9"are provided with such a switch.

The switch is controlled by a control circuit according to the invention. When the control circuit latches a"on"signal into the driver, the switch 11 is switched off, so that the current flows through the light emitter and it is turned on. When the control circuit latches an"off"signal the switch 11 is switched on, and current is lead around the light emitter to the succeeding light emitters of the string. The central control

device 12 is shown in the lower part of the drawing together with the control circuits 13,13', 13", 13"', and 13"". It is apparent from the drawing that the control circuits are serially connected and that one string of control circuits may control several sub- strings of light emitters.

The signals for the circuit are conveniently provided by a personal computer but the invention contemplates any kind of device capable of producing the required output.

When a personal computer is used for controlling the circuit, the frequency of the clock signal is limited to the clock frequency of the computer used. One problem associated with using a personal computer for controlling the circuit direct, is that the processing units of a personal computer are sometimes busy doing other things than controlling the circuit. Therefore it is an advantage to make the program on a computer and load it into a device with a memory for the program and at least one data-output. Advantageously the device also has a clock-output and a latch output.

According to an especially preferred embodiment the device also comprises a proc- essor adapted to run the program.

Examples The method and the system according to the present invention can be used advan- tageously for controlling the lights on a string of lights for a Christmas tree or for decoration of shops. Other contemplated uses include light shows, e. g. in disco- theques, concert halls, theatres, tourist attractions etc.

Another system where the method and the system of the present invention may be advantageously be applied is the control of lights, light signals, power supply to the rails, and railway points or switches in toy railway systems. Such railway systems are characterised by a high number of switches and according to prior art a complex wiring system. Such a system can be controlled according to the present invention by having all switches arranged in serial connection using one, two or three wires.

Similarly the method and system of the present invention can be used for controlling fountains. The system and method are especially adapted for simultaneously con- trolling both the fountains, which are controlled by a number of valves, and an ac- companying light show, controlled by a number of light emitters.

The system may also conveniently be used for controlling the light intensity of cer- tain pre-determined light emitters on the string by switching on and off a particular light emitter so frequently that the naked eye cannot detect the switching. If for in- stance a particular light emitter is turned off half of the time it will appear to the na- ked eye as emitting approximately 50 % of the light compared to a light emitter be- ing constantly on.

The invention also contemplates the use of the method and the system for control- ling motion pictures on a large screen. Such screens are typically made by having a multiplicity of rows and columns forming the points of the screen. Each single point consists of three coloured light emitters (red, blue, and yellow). The colour of each single point as perceived by the spectators is provided by turning on and off the three light emitters so that every mixture of percentages of the three colours can be produced. The method and system of the present invention is highly suitable for controlling the light emitters of such large screens.

Similarly it is contemplated that the method and system of the present invention can be used for controlling an electric newspaper which also comprises a multiplicity of light emitters, which can be arranged in serial connection.

In general, the control circuit according to the invention may be used for controlling any kind of switch. It is especially advantageous for controlling large number of switches, which need to have their signal changed according to a pre-determined program. Thus, apart from controlling light emitters, the switch unit may control valves, relays, engines, hydraulic devices, pneumatic devices, heating and cooling devices, stirring devices. The control circuit is thus adapted for controlling any kind of automated industrial process, such as industrial robots, production lines, process control, etc.

According to a final aspect of the invention, the system and the method may also be used for the reverse process, namely the process of collecting data from a number of detectors on a string to a central unit, such as for instance a computer. In this way, data from a large number of detectors can be transferred rapidly and frequently to the central unit. This aspect of the invention may be used for transferring data

from for example a survey system for surveying doors, windows and lights in a building. The method may also be used for collecting data during an industrial proc- ess and thus be used for performing process control. The signals transmitted in this case will be the condition of the doors and/or windows (open, closed) and lights (on/off). The string of detector units may also comprise movement detectors, which provide a signal (movement or no movement) to the central unit. The detector units may detect movement, light, temperature, the open or closed condition of door, win- dows, drawers or the presence of or voltage of a current in an electrical circuit.