The invention relates to the field of the input terminals for electronic arrangements and offers a novel method of and a very simple optoelectronic keyboard for generating input signal assigned to the depressed positions of keys. The input signals are generated according to the invention on optoelectronic basis, without electric contact between movable elements, by means of an arrangement which can easily be taken into mass- -production.

The electric contacts for realising current paths are not acceptable in the keyboards constituting input terminals for' electronic arrangements, as computers, data processing means etc. because of limited reliability of the connection and other effects. This is the basis or realising the contactless key¬ boards which are known in more embodiments. One of them is the optoelectronic keyboard described e.g. in the U.S. Letters Patent No. 4,278,965 granted on July 14, 1981 to Nelson et al. The optoelectronic keyboards are less sensitive to the outer disturbing factors than the other keyboards realised without electric contact of the movable elements. The essence of this arrangements is that on pushing the key interrupts the light path of two light sources arranged in a matrix comprising more light sources for determining rows and arrows. Hence, the place of interruption can be assigned to two light sources and on this basis it is possible to determine which key has been de¬ pressed. The light patha require keys of relatively sophisticat shape and because of applying a higher number of detection

channels the keyboard is expensive, its production requires much work. A 'further disadvantage is that the depressed key can block the detection of another depressed key what results in errors during data processing, programming etc. This problem can be avoided either by applying a sophisticated electronic arrangement or by further complication of the mechanical shape as it is shown in the U.S. Letters Patent cited above. This comprises a proposal for a novel shape of the key in order to avoid the problem of double depression. The present invention is related to avoiding the above mentioned disadvantages of the optoelectronic keyboards.

The invention is based on the recognition that the identif cation of the keys can be done by sequential lighting up light sources replacing thereby the spatial matrix of light sources with detecting of lighting up.

The objects of the present invention are a method and an optoelectronic keyboard whereby the input signals of an electro ic arrangement can be produced in a simpler and cheeper way than by the known keyboards. The proposed keyboard can be especially adantageously applied in microprocessor units pro¬ duced in high mass and exposed to extensive load as in telephone apparata, cash-registers further in computers and in units of similar electronic equipment.

Thus, the proposed method comprises the steps of depressin - e.g. according to a predetermined program sequence - keys from a starting position to an end position, thereby changing the propagation conditions of light emitted by light sources, detecting the light of the light sources, generating an input

signal corresponding to the key depressed to the end position, and returning - when appropriate - the key into the starting position, wherein each key is assigned to a respective light source. The essence of the invention lies in assigning a respective light source to each of the keys, lighting up the light sources in a predetermined sequence, with appropriate time interval, e.g. with a given frequency after one another, covering one of the light sources by the depressed key, sensin the lack of the light emitted by the covered light source and generating the input signal on sensing the lack of the light. In a practical realisation it is advantageous to select high frequency range of about 10 kHz and to generate the input signal after sensing the lack of the light from the given light source sometimes after one another. The method as proposed by the invention can be implemente by an optoelectronic keyboard, the essence of which lies in forming an inner space in the key for covering the light source in the depressed position of the key, wherein the light sources are connected to an electronic control unit actuating them in a predetermined sequence. It is advantageous to apply a trans¬ lucent layer in the closed housing of the keyboard, wherein the layer comprises openings receiving the light source and the assigned key when depressing the last.

Further advantages and features of the proposed method and optoelectronic keyboard will be apparent when regarding the fol lowing detailed description together with the attached drawings wherein Pig. 1 shows a 16-key keyboard,

Pig. 2 is the cross-section A-A of the keyboard shown in Pig.l having the proposed construction, Pig. 3 is a proposed embodiment of an electronic control unit, Pig. 4 is the schematic diagram of a light sensing channel, an Pig. 5 shows the time diagram of control and timing signals applied in the electronic control unit. When implementing the method as proposed by the invention one of light sources arranged in a closed space is covered by a key arranged over the light source. The light sources are sequentially lighted up and the light is sensed. The keys _. and the light sources are assigned to one another, thus, appearanc of the light signalizes the key not being depressed. The de¬ pression of the key results in covering the light source and thereby in lack of sensing the light emitted by this source. The key is identified in this way and the appropriate input signal to the electronic arrangement can be generated.

In order to avoid errors in detecting the lack of light, and especially when the sequences are repeated in high frequen cycles it is advantageous to apply some techniques of improvin the reliability of sensing. This can be done in the way that the input signal is generated not after the first detection of the lack but after sensing more, e.g. five or ten lacks of light. One possibility thereof lies in interrupting the sequen of the lighting up and in actuating the given light source som times one after another and in generating the input signal after determining that more, e.g. eight lightings up of the gi light source haven't resulted in sensing the light. The other possibility is to follow the sequences 'and to store the key or

light so urce without detecting the light and to generate the input signals when the same light source is not detectable in a higher number of sequences, e.g. in three. Of course, the light source out of order should be detected by the well-know

_* other methods, in order to avoid erroneous generating.

The optoelectronic keyboard proposed by the invention /Pig. 1 and 2/ comprises a field of keys B arranged on a black covering plate 2 made of material being not translucent. The keys B are supported by springs 5. Under the covering plate 2 is a basic plate 1 made also of material being not translucent bearing light sources P arranged underneath the keys 3. The space limited by the covering plate 2 and the basic plate 1 is closed from lateral side by appropriate wall elements in order to allow no light to come into this space. Among the wal elements a light sensing unit 3 can be arranged. If appropriat a higher number of light sensing units 3 can be applied, e.g. four, one for each side around the field of the keys B. It is also possible to arrange one or more light sensing units 3 in the inner space, underneath the field of the keys B. In the inner space limited by the covering plate 2, the basic plate 1 and the wall elements propagation of the light to the light sensing unit/s/ 3 can be ensured by different means; One of them is to cover the inner surfaces limiting the inner space by a layer of light reflecting material. The other is to arrange in the inner space - and this can be done also in case of preparing the light reflecting layers - a trans¬ lucent layer 4 made of glass or plexiglass wherein the light emitted by the light source reaches the light sensing unit 3

after one or more refle ction. In t he translucent layer 4 ope ings 7 are prep ared with dimensions greater than that of the key B . The l ight sources are connected to an ele ctronic contr unit 8. ^* The light sources P are lighted up , as ment ioned, in a predetermined time sequence , one after another. The key B hav an inner space 6 closed from l ateral side covers the light so P assigned to it when depressing the key B . In this way the light of the covered light source P can not reach any of the light sensing units 3.

The lighting up of the light sources P , as mentioned, is cyclically carried out in a predetermined time sequence. This is done advantageously with a given frequency rather than wit a stochastically changing time interval between the lightings up. According to the experience it is possible to ensure fre¬ quency range up to 10 kHz by simple means without any reliabi problem. The frequency value 10 kHz is sufficient when actuat ing up t o 100 keys with normal speed of typing. The mentioned fre quency and the speed ensures the highly reliable generatin of input signals corresponding to the keys actuated.

In the keyboard as proposed by the invention the light o the light sources P pro pagate s through the translucent layer ■ and/or by reflections from the surfaces of the covering plate and basic plate 1 facing one another. At t he end of thi s path the light reaches the light sensing unit/s/ 3. If the intensi of the light so urces P is high and t he space underneath the keys B is limited it is not necessary to apply the translucen layer 4. When pr ep aring a keyboard having greater dimensions

and/or sophisticated shape it is advantageous to apply the tra lucent layer 4. In this case the basic plate 1 can bear a prin ed circuit arrangement connecting the light sources 8 to the electronic control unit 8. A ve'ry important feature of the invention should be seen in actuating the light sources P in a controlled way. The control of the actuating can be ensured e.g. by a circuit ar¬ rangement 8 shown in Pig. 3. Of course, the control can be en¬ sured by other circuit. arrangements, too. In the circuit arran ment shown in Pig. 3 sixteen light sources P are assigned to sixteen keys B according to Pig. 1. One terminal of the light sources P is connected to respective outputs of a row driving unit M, controlled from input lines S _T , S2 _» So and S4, and the other terminal thereof is coupled with respective outputs of an arrow driving unit M ₂ controlled from input lines Q± , O2,

0-j and 0,. Either the row driving unit M^ or the arrow driving unit ₂ is equipped w th a permitting input Ξ ^' whereby in appropriate conditions and in an appropriate time moment one of the light sources arranged in a matrix can be made light up. The light sensing units 3 ^' can be connected in series or in parallel according to their type, if a higher number there¬ of is applied /Pig. 4/. Their output signal being the sum of the input signals is led to an amplifier A which is capable of forming the output signal. The amplifier A generates at its output P a signal which is capable of causing the lighting up of the next light source P in the sequence. The lack of the signal on the output P, if in the same time a light source P has lighted up, is the basis of generating an input signal for

the outer electronic arrangement, said signal being involved b the lack of sensing a light signal according to the principles shown in the implemented ways of realising the method.

The electronic control arrangement 8 shown in Pig. 3 forwards on the input lines S^- , S ₂ , S^, Si, 0-^, 0 ₂ , 0, and 0. signals shown in respective lines of Pig. 5. signed by the same references. The sensed signals of the light sources P are shown in the lowest line. As it can be seen, under the in¬ fluence of the signals forwarded through the permitting input E the signals are generated for every one of the light sources and they are detected, except the signal signed by J, consti¬ tuting in the present case the signal corresponding to the lighting up of the sixth key B.

The electronic arrangement 8 of the optoelectronic key- board proposed by the invention can be realised on a printed circuit plate forming the basic plate 1.

By means of the method according to the invention a key¬ board is capable of controlling in a highly reliable way the generating of output signals for an electronic arrangement. The keyboard as it can be realised on the basis of very simple light sources, as light emitting diodes, and it requires no mechanical elements of sophisticated shape. It has only one light propagation space, this simplifies and makes cheeper the production of the keyboard.