EP0097718A1

EP0097718A1 - Telephone hook switch

Info

Publication number: EP0097718A1
Application number: EP19830900757
Authority: EP
Inventors: Henry A. Harris Corp. STROBEL
Original assignee: Harris Corp
Current assignee: Harris Corp
Priority date: 1982-01-04
Filing date: 1983-01-04
Publication date: 1984-01-11
Also published as: WO1983002514A1

Abstract

Nouveau commutateur amélioré particulièrement adapté à être utilisé avec un téléphone. Plus particulièrement, commutateur électro-optique pouvant fonctionner dans n'importe quelle condition d'éclairage ambiant. Le commutateur comprend un générateur d'ondes carrées (20) dont une sortie est reliée à un photo-émetteur (22). Un photo-détecteur (26) est disposé de sorte que la lumière (24) produite par l'émetteur (22) soit reçue par le détecteur (26) lorsque les éléments du téléphone se trouvent dans une première position alignée. Le signal de sortie provenant du détecteur (26) est envoyé à un circuit logique (30) de même que le signal de sortie provenant du générateur (20). Le circuit logique (30) est conçu de sorte que lorsque les éléments du téléphone se trouvent dans la première position alignée et que le signal de sortie de l'émetteur (22) est reçu par le détecteur (26), un premier signal de sortie est produit. Par contre, lorsque les éléments du téléphone se déplacent l'un par rapport à l'autre, en désalignement, le détecteur (26) produit un signal de sortie qui est fonction des conditions ambiantes d'éclairage, et le circuit logique (30) produit un deuxième signal de sortie.New improved switch particularly suitable for use with a telephone. More particularly, an electro-optical switch capable of operating in any ambient lighting condition. The switch includes a square wave generator (20), one output of which is connected to a photo-emitter (22). A photo detector (26) is arranged so that the light (24) produced by the transmitter (22) is received by the detector (26) when the telephone elements are in a first aligned position. The output signal from the detector (26) is sent to a logic circuit (30) as is the output signal from the generator (20). The logic circuit (30) is designed so that when the telephone elements are in the first aligned position and the output signal from the transmitter (22) is received by the detector (26), a first output signal is produced. On the other hand, when the elements of the telephone move relative to each other, in misalignment, the detector (26) produces an output signal which is a function of the ambient lighting conditions, and the logic circuit (30) produces a second output signal.

Description

Telephone Hook Switch

Technical Field

The subject invention relates to a new and improved switch particularly adapted for use with a telephone. More particularly, an electro-optical switch is disclosed which is operable in any ambient light conditions.

All telephones require some form of switch means for activating the circuitry when a user wishes to place a call. The most common form of switch includes a spring biased mechanical contact. For example, on a typical desk top telephone, a pair of spring biased members are located in the cradle. When the user wishes to place a call, the handset is lifted from the cradle permitting the spring biased members to rise, activating the telephone circuit. When the call is completed, the handset is replaced in cradle, depressing the members, thereby breaking the circuit.

These types of mechanical contacts are satisfactory for conventional telephone use. However in certain applications, mechanical switches are undesirable. More particularly, when spring biased contacts are released they tend to rebound or bounce. The bouncing of the contacts will generate signals or electrical pulses. The pulses do not seriously affect normal voice connections, however, they can interfere with high speed communications. For example, when the telephone is used as an interface between computers, data transmission is carried out at high speed and any spurious pulses will result in transmission errors.

Accordingly, in the prior art, various electrical circuits were developed to eliminate the pulses generated by the rebounding of mechanical contacts. While these "debouncing" circuits functioned to suppress spurious signals generated by the mechanical contacts, efforts were made to develop nonmechanical switches which would not generate any pulses.

Nonmechanical switches offer the additional advantage of having no moving parts which could wear out.

One form of nonmechanical switching device includes the use of photodetectors. The simplest type of photodetector switch is one which is actuated by the reception of the ambient light in the room. In use, the photodetector is mounted so that it is shielded from ambient light when the handset rests on the cradle of the telephone. When the user wishes to make a call and picks up the handset, the photodetector is exposed to the light in the room and generates a current which can be used to actuate the telephone circuit. Unfortunately, this type of system is highly unreliable because it is dependent upon ambient light conditions for actuation. Stated differently, if the light present in the room is not enough to cause a trigger voltage to be generated, the phone circuit will not be actuated.

An improvement over the latter photodetector configuration includes the provision of a photoemitter. More particularly, a photoemitter can be located in a manner to continually actuate the photodetector when the handset rests in the telephone cradle. This result can be achieved by mounting the photodetector and emitter in alignment, on opposed elements of the telephone. By this arrangement light generated by the emitter is transmitted to and received by the detector.

In the alternative, reflective photodiode assemblies have been developed wherein both the detector and emitter are mounted on the same telephone element in a manner such that the remaining element of the telephone reflects light generated by the emitter back into the detector. In either construction, the prior art switch was designed such that when the handset of the telephone is removed from the cradle to place a call, the light from the emitter will not be received by the detector. The absence of light received by the detector will prevent any current from being generated. The absence of current can be used as a signal to actuate the telephone circuit.

Unfortunately, the latter prior art switches could also be adversely affected by ambient light conditions. As stated above, when the handset is removed from the cradle, no light from the emitter will reach the detector. However, if the ambient light in the room is sufficiently strong, the detector could nonetheless be improperly actuated. One method employed in the prior art to overcome the latter shortcoming was to provide an emitter which generates infra-red light. The latter emitter was coupled with a detector which was selected or filtered, such that only infra-red light would generate a current. By this arrangement, visible light in the room would not actuate the detector. However, in practice, high intensity incandescent bulbs frequently give off a large amount of infra-red radiation which will cause the improper actuation of the switch. Thus, it would be desirable to provide a new and improved nonmechanical electro-optical switch device which operates independently of ambient light conditions.

Disclosure of the Invention

Accordingly, it is an object of the subject invention to provide a new and improved switch particularly adapted for use with telephones.

It is another object of the subject invention to provide a new and improved switch which operates without mechanical contacts.

It is a further object of the subject invention to provide a new and improved nonmechanical switch which does not require debouncing circuitry to eliminate spurious pulses.

It is still another object of the subject invention to provide a new and improved photo-optical switch which operates independently of ambient light conditions.

In accordance with these and many other objects, the subject invention provides a switch means particularly adapted for use with a telephone. The switch includes a photoemitter and detector combination which are disposed in a manner such that when the phone is in the aligned, on-hook condition, light generated by the photoemitter is received by the photodetector. As in the prior art, the photoemitter

co bination can be a reflective or trans issive array.

The subject invention further includes a generator capable of producing an oscillating signal having a frequency on the order of 10,000 kilohertz. The output of the generator is supplied to the photoemitter such that high frequency light pulses are generated. By this arrangement, when the telephone elements are in the aligned position, such that the photodetector is receiving the pulsed light generated by the emitter, the detector will generate high frequency electrical pulses, identical to the output of the generator.

In accordance with the subject invention, a logic circuit means is connected to the photodetector as well as to the square wave generator. The logic circuit means is configured to produce a first output signal when the inputs from the generator and the photodetector are the same. In addition, the logic circuit means will produce a second output signal when the inputs received are different. As mentioned above, when the telephone is in the aligned position, the output from the photodetector is identical to the output from the generator. Accordingly, in this situation, both the inputs to the logic circuit means are identical, such that the first signal is produced and can be used to indicate the on-hook condition.

In contrast, when the handset of the telephone is removed from the cradle, the photodetector will no longer receive the pulsed light from the emitter. Rather, the photodetector will receive whatever ambient light is available in the room. The output of the detector is therefore dependent upon the ambient light conditions. This output is supplied to logic circuit means along with the output from the generator. Since the output from the detector is different from the pulsed signal of the generator, the logic circuit means will produce the second output signal and can be used to actuate the telephone circuitry.

In the preferred embodiment of the subject invention, the logic circuit means includes an "exclusive-or" gate. As well known in the art, an exclusive-or gate produces a first or low output when the inputs thereto are identical. In contrast, whenever the inputs are different, a second or high signal is generated. Thus, in use, when the handset is resting in the aligned position on the cradle of the telephone, and the pul^~sed light produced by the emitter is received by the detector, the output produced by the detector is identical to the generator. When these identical outputs are supplied to the exclusive or gate, the first, low signal is produced. When the handset is removed from the telephone, the inputs to the gate are different so that the second, high signal is produced. In the preferred embodiment, the output from the gate is integrated and compared to a reference voltage in order to generate a signal which can be used to actuate the telephone circuits.

Further objects and advantages of the subject invention will become apparent from the following detailed description when taken in conjunction with the drawings in which:

Brief Description of the Drawings

Figure 1 is a block diagram illustrating the new and improved switch of the subject invention.

^ Figure 2 is a circuit diagram illustrating the component parts of the new and improved switch of the subject invention.

Figure 3 is a graph illustrating the types of inputs received by the logic circuit means of the switph of the subject invention.

Best Mode for Carrying Out the Invention

Referring to Figure 1 , the new and improved switch 10 of the subject invention is illustrated. Switch 10 is a photoelectrical device which is operable in all ambient light conditions. Switch 10 is particularly adapted for use as an indicator in a telephone system where data link communications are involved. As discussed above, the bouncing of the contacts associated with typical mechanical switches frequently introduce spurious pulses into the communication line which will interfere with data transmission. Accordingly, various electro-optical switches were developed to eliminate the mechanical contacts. However, the prior art switches operated effectively only under optimum ambient light conditions. As described more fully herein below, the subject switch 10 is operable in any ambient light situation.

In accordance with the subject invention, a generator means 20 is provided for producing an oscillating output. In the preferred embodiment of the subject invention, generator means 20 is configured to output a square wave signal of transitor-transitor logic (TTL) pulses alternating between zero and +5.0 volts. Generators of this type are well known in the art and need not be further described. The output of generator means 20 is supplied to a photoemitter 22. Photoemitter 22 is configured to generate light in response to the pulses supplied by the generator means 20. As illustrated in Figure 2, photoemitter 22 is preferably defined by a photodiode. Photoemitter 22 is paired with a compatible photodetector 24 capable of generating an electrical output in response to the reception of light 24.

In accordance with the subject invention, the emitter and detector are mounted to the elements of the telephone in a manner such that light generated from the emitter is received by the detector only when the elements are in an aligned position. For example, when used with a typical desk top telephone, one of the optical elements can be affixed to the base of the telephone while the remaining element is affixed to the handset. The optical elements are mounted in a manner such that when the handset is in place in the cradle on the telephone, light generated by the photoemitter 22 is received by the photodetector 26. However, when the handset of the telephone is removed from the cradle, such that the optical elements are no longer aligned, light from the emitter is unable to reach and actuate the detector.

In the latter example, a transmissive photoemitter detector system is described. In addition to transmissive systems, various other emitter detector systems are known and used in the prior art. For example, reflective photodiode assemblies are known, which are formed as a single unit, wherein light generated by the emitter is reflected back and received by the integrally associated detector. If the latter

C^'_Ή \ type of assembly were used in conjunction with the subject invention, it could be mounted, for example, on either the handset or the base of the telephone in a position such that the remaining element of the telephone acts as the reflecting surface when the handset rests in the cradle of the phone. By -this arrangement, the removal of the handset from the cradle breaks the reflecting path such that only ambient light will be received by the detector.

It is to be understood that the scope of the subject invention is not intended to be limited by the type of photoemitter detector assembly used. It is merely necessary to provide an assembly wherein light generated by the photoemitter is only received by the photodetector when the elements, whose movement is to be sensed, are in an aligned position. Therefore, when the elements are moved out of the aligned position, the detector will no longer receive light generated by the emitter, but rather will receive any form of light available in the environment. It is intended that the subject switch be utilized with any devices where the use of mechanical switches is undesirable.

In accordance with the subject invention, the electrical output generated by the photodetector 26 is supplied to a logic circuit means 30, illustrated by the broken lines in Figure 1 and 2. The output of generator means 20 is also supplied to logic circuit means 30. Logic circuit means 30 is designed such that it will generate a first output signal when the inputs A and B, from the generator and detector means respectively, are similar. In addition, logic circuit means 30 will generate a second output signal whenever the inputs A and B are different. The first and second output signals can be utilized to indicate whether the elements are in an aligned position.

A brief summary of the operation of the subject switch 10 will be provided using a telephone installation for reference. As discussed above, when the handset is resting in the cradle of the telephone, which corresponds to the first aligned position, light 24 generated by photoemitter 22 is received by photodetector 26. Emitter 22 generates a pulsed output in response to the pulsed input of generator 20.

Accordingly, detector 26 will generate a similar pulsed output when receiving the pulsed light from the emitter. The pulsed output from the detector is supplied to input B of logic circuit means 30. As illustrated in Figures 1 and 2, input A of logic circuit means 30 is connected directly to generator 20 and therefore is also supplied with a pulsed signal. As discussed above, when the inputs A and B to logic circuit means 10 are the same, the first output signal is produced. Thus, when the telephone elements are in the aligned first position, the subject switch 10 will generate the first output signal.

In the situation where the handset is removed from the base of the telephone, the photodetector 26 will no longer receive the light generated by the photoemitter. Rather, the signal generated by the photodetector will be dependent upon the ambient light in the room. The type of output generated by the photodetector in this situation will be described more fully below. Nevertheless, it is apparent that the output generated by detector 26, and supplied to input B of the logic circuit means 30, will not be similar to .the pulsed signal produced by generator means 20 and

ΓT. r supplied to input A. As stated above, when the inputs to logic circuit means 30 are different, a second output signal will be generated which can be used to illustrate the off-hook condition.

Referring now to Figures 2 and 3, the construction of the subject switch 10 will be. described in detail. As stated above, generator means 20 is intended to produce a continuous series of TTL pulses. An example of the pulse train produced by generator means 20 is illustrated in Figure 3A. The output signal of generator 20 is supplied directly to input A of logic circuit means 30. In the preferred embodiment of the subject invention, the frequency of the TTL pulses is on the order of 10 kilohertz.

The signal supplied to input B of logic circuit means 30 is dependent upon the light received by photodetector 26. With particular reference to Figure 2, when no light is received by phototransistor 26, the transistor network (26, 32) will be nonconducting. Accordingly, a high or +5.0 voltage signal from source 34 will be supplied to input B, as illustrated in Figure 3B. In contrast, when continuous light is received by phototransistor 26, the transistor network (26, 32) will conduct, permitting the current from source 34 to pass to ground. Accordingly, a low or zero voltage signal, as illustrated in Figure 3C, will be supplied to input B.

The light received by detector 26 is dependent upon ambient light conditions when the telephone is in the off-hook condition, and dependent upon the output from the photoemitter 22 when the telephone elements are in the aligned first position. For example, when the telephone is in the off-hook condition, and the ambient light in the room is insufficient to actuate detector 26, a high or +5.0 voltage signal, as illustrated in Figure 3B will be supplied to input B. In contrast, if the ambient light is strong enough to actuate defector 26, a low signal, as illustrated in Figure 3C, will be supplied to input B.

The remaining situation concerns the type of signal supplied to input B when the telephone is in the aligned first position, such that the light generated by emitter 22 is received by detector 26. As stated above, the pulsed output from generator 20 is supplied to emitter 22. With reference to Figure 2, it will be seen that when the output from generator 20 is high (e.g. equal to +5.0 volts) no current will flow from source 34 through diode 22. Accordingly, no light will be generated and no light will be received by detector 26^'. As discussed above, when no light is received by detector 26, a high signal will be supplied to input B. Thus, when the output from generator 20 is high, a high signal is supplied to input B.

In contrast, when the output from generator 20 is low, current will flow through diode 22, causing light to be generated which is received by detector 26. When light is received by detector 26, the transistor network (26, 32) is conductive and a low signal is supplied to input B. Thus when the output from generator 20 is low, a low signal is supplied to input B.

Accordingly, the subject switch is configured such that when the elements of the telephone are in the aligned position and light from the emitter is received by the detector, the signal supplied to input B follows and is identical to the output from generator 22, supplied to input A. Figure 3D illustrates the signal at input B in the latter situation which is identical to the signal at input A as illustrated in Figure 3A. It is to be understood of course that while the path from generator 20 to input B is longer than the path to input A, transmission is virtually instantaneous, such that the signals supplied to the inputs are effectively identical.

Having discussed the character of the signals supplied to inputs A and B under various conditions, the construction and operation of logic circuit means 30 will now be described in detail. In accordance with the subject invention, logic circuit means 30 includes an exclusive-or gate 40. As is well known in the art, an exclusive-or gate is a logic device which will generate a low or zero voltage output when the inputs thereto are the same. In addition, an exclusive-or gate will generate a high or +5.0 voltage signal when the inputs thereto are different.

Input A of gate 40 is supplied with a continuously oscillating pulsed signal from generator 20 as illustrated in Figure 3A. As discussed above, when the telephone is in the aligned first position, such that light generated by emitter 22 is received by detector 26, a pulsed signal, of identical character, is supplied to input B (Figure 3D) . Thus, the signals received at the inputs are either simultaneously high or low. Stated differently, when the telephone elements are in the aligned position, the inputs to gate 40 are identical at any given instant of time. Therefore, the output at point C of gate 40 will be

OMPI continuously low.

In contrast, when the elements of the telephone are moved out of the aligned position, the signal at input B will no longer be identical to the signal at input A. As illustrated in Figures 3B and 3C, the signal will be either continuously high or low depending upon the ambient light conditions in the room.

The output from gate 40, at point C, will be the same for either of the continuous signals illustrated in Figures 3B and 3C. More particularly, gate 40 will generate a series of pulses having a frequency equal to the oscillation frequency of generator 20. This result is achieved since the signal at input A oscillates between high and low values, such that it will alternate between being the same and opposite with respect to the continuous signal supplied to input B. Thus, when the inputs are the same, a low signal will be output, and when they are different, a high signal will be output. The remaining components of logic circuit means 30 function to convert the oscillating output at point C to a continuous second output signal.

The output signal from gate 40 is supplied to an integration means 50. Integration means 50 consists of a resistor-capacitor network. Resistor-capacitor networks are well known in the art and need not be described in detail. Briefly, the integration means 50 functions to convert an oscillating signal into a level voltage signal. The selection of the component values of resistor 52 and capacitor 54 determine the operating characteristics of the integration means 50. In the preferred embodiments of the subject invention, where generator 20 oscillates at 10 kilohertz, the resistor may be 20 Kohms and the capacitor is 0.1 microfarads. In use, when an oscillating signal, corresponding to the non-aligned off-hook condition, is passed through integration means 50, a continuous signal of approximately 2.5 volts is supplied to comparator means 60. When a continuous low or zero voltage signal, characteristic of the on-hook aligned position, is supplied to integration means 50, it will of course pass through unaffected. In the latter situation, any spurious pulses or glitches in the low signal will be filtered by capacitor 54.

Comparator means 60 functions to compare the signal, supplied by integration means 50, with a reference voltage. The level of the reference voltage is selected to differentiate between the signals, generated by integration means 50, corresponding to both the on and off-hook conditions. As discussed above, in the on-hook condition, a low level or zero voltage is generated while a voltage of approximately +2.5 volts is generated during the off-hook condition. Accordingly, a reference voltage falling in the range of +1.0 and +1.5 volts is suitable. The level of the reference voltage is determined by the values of the voltage divider resistors 62 and 64. In the preferred embodiment, resistors 62 and 64 are 33 and 10 Kohms respectively, which produces a reference level at point 68 of +1.16 volts.

Comparator 60 functions to generate a low output signal when the voltage at input 70 is less than the reference voltage at input 68. In the alternative, comparator 60 will generate a high signal when the voltage at input 70 is greater than the reference voltage. As discussed above, in the on-hook condition, a low or zero voltage is supplied to input 70 such that a low or first output signal is generated by comparator 60. In the off-hook condition, a 2.5 volt signal is supplied to input 70, which is greater than the reference voltage, such that a high or second output signal is generated. The difference between the outputs can be used to distinguish the on and off-hook conditions.

It is well known that the output from a resistor- capacitor integrator will have a slight, but finite ripple. A ripple in the signal often results in a degree of uncertainty in the operation of the circuit near the comparator threshold. This uncertainty can be overcome by providing the comparator with a hysteresis type characteristic. A hysteresis effect can be achieved by coupling a large resistor (not shown) from the output of the comparator to the non-inverting input, thereby creating a positive feedback loop. In the alternative, the comparator can be replaced with a integrated circuit, such as a Schmitt trigger, having appropriate characteristics.

In the preferred embodiment of the subject invention, logic circuit means 30 further includes a photodiode 80 to provide a visual indication of comparator output. Diode 80 is connected such that when the comparator output is low, corresponding to the on-hook condition, current will flow through diode 80 from source 82 causing the diode to emit light. In contrast, when the output from comparator 60 is high, no current will flow through diode 80 and no light will be generated.

o:.:?l Having described the components of the subject switch 10 in detail, its operation will now be summarized. When the elements of the telephone are disposed in the aligned, first position, the pulsed light generated by the photoemitter 22 is received by^' the photodetector 26. The signal supplied to input B of gate 40 is a function of the actuation of detector 26. Thus, in the latter situation, a pulsed signal is supplied to input B, corresponding to the pulsed output of generator 20. Since the signal received at input A is supplied directly from the generator, both inputs to gate 40 will be the same, such that a low signal is output at point C. Comparator 60 will also generate a low, first signal since the output signal from gate 40 is below the reference voltage1

In. contrast, in the off-hook condition, the signal at input B will not correspond to the signal at input A. Typically, either a continuously high or low level signal is supplied to input B, depending upon whether the ambient room conditions are dark or light respectively. Input A will oscillate between being similar and different with respect to input B, such that the output signal of comparator 40 will be pulsed.

Integration means 50 functions to convert the pulsed signal from gate 40 into a continuous voltage level which is supplied to comparator 60. Since the voltage level is greater than the reference level, a high or second output signal is generated.

One of the distinct advantages of the subject switch 10 is that it is operable under all ambient light conditions. More particularly, the on-hook

o:-.~ - condition will only be indicated when detector 26 receives a pulsed input identical to the output of generator 20. The off-hook condition is indicated when any other signal is received at input B. Thus, if the room is dark, and detector 26 is not actuated, a continuous high signal is supplied to input B. If the room contains light of sufficient intensity to activate detector 26, a continuous low signal is supplied to input B. It makes no difference what type of light is present, such as visible or infra-red radiation.

Further, the type of light to which the detector is sensitive is irrelevant as long as it is sensitive to the light produced by the emitter.

The subject switch is also operable in a situation where the ambient light is generated from a pulsed source. For example, some sources generate light at a standard frequency of 60 cycles per second. Thus, in the off-hook condition, a signal having pulsed nodes occurring at a frequency of 60 cycles will be supplied to input B of logic circuit means 30. As can be appreciated, a signal having pulsed nodes at 60 cycles is substantially different from the input of generator means 20 which oscillates between high and low values at 10,000 cycles per second. Thus, even if both signals were coincidently in phase, for each cycle at input B, 150 cycles will be supplied to input A, such that a pulsed output will be generated by exclusive or gate 40. The pulses are integrated to produce a voltage greater than the reference voltage resulting in a high output signal from comparator 60. It is apparent that the only light source which will cause a signal to be generated corresponding to the aligned position of the telephone is one which oscillates in phase and at a frequency equal to the output of generator means 20. The frequency of the generator means 20 is chosen such that the possibility of encountering ambient light having a similar frequency is eliminated.

In summary, there has been provided a new and improved switch 10 for indicating whether one element has been removed from an aligned first position relative to another element. The subject switch includes a generator means 20 for producing an oscillating output. A photoemitter means 22 is provided for generating light in response to input from generator means 20. A photodetector means 26 is provided which is disposed in a manner such that light generated by the emitter is received by the detector only when the elements are in an aligned first position. The electrical output generated by the detector is supplied to a logic circuit means 30. Logic circuit means 30 is also supplied with the output from generator means 20.

Logic circuit means 30 is configured to output a first signal when the inputs received from the generator and the detector are similar and a second output signal when the inputs are different. By this arrangement, when the elements are in the aligned first position, and the light generated by the emitter is received by the detector, the detector generates an output similar to the generator causing the logic circuit means to generate the first output signal. When the elements are moved relative to one another, out of the aligned first position, such that the light generated by the emitter is no longer received by the detector, the detector generates an output different from the generator causing the logic circuit means to produce the second output signal. When the elements are moved from the aligned first position, the subject switch will produce the second output signal regardless of the ambient light conditions.

While the subject invention has been described with reference to a. preferred embodiment, it is to be understood that various other changes and modifications could be made therein, by one skilled in the art, without varying from the scope and spirit of the invention as defined by the appended claims.

Claims

1. A switch for indicating whether one element has been removed from an aligned first position relative to another element comprising:

generator means for producing an oscillating output;

emitter means connected to the generator means for generating radiation in response to the input from the generator means;

detector means for generating an electrical output in response to the reception of radiation, said emitter and detector means being affixed to the elements in a manner such that radiation generated from the emitter means is received by the detector means only when the elements are in the aligned first position; and

logic circuit means, connected to the generator means and the detector means and generating a first output signal when the inputs received from both the generator means and the detector means are similar and a second output signal when the inputs received are different, whereby when the elements are in the aligned first position, and the radiation generated by the emitter means is received by the detector means, the detector means generates an output similar to the generator means such that the logic circuit means generates the first output signal and when the elements are moved relative to one another, out of the aligned first position, such that the radiation generated by the emitter means is no longer received by the detector means, the detector means generates an output different from the generator means such that the logic circuit means generates the second output signal.

2. A switch as recited in Claim 1 wherein the logic circuit means includes an exclusive-or gate generating a first low signal when the inputs thereto are similar and generating a second high signal when the inputs thereto are different.

3. A switch as recited in Claim 2 wherein the logic circuit means further includes an integration means connected to the exclusive-or gate for converting any pulse type output therefrom into a continuous output.

4. A switch as recited in Claim 3 wherein the logic circuit means further includes a comparator means connected to the integration means for comparing the output from the integration means with a reference level.

5. A switch as recited in Claim 3 wherein the integration means consists of resistor-capacitor network.

6. A switch as recited in Claim 1 wherein the emitter means is affixed to one of the elements while the detector means is affixed to the remaining element in a manner such that when the elements are in the aligned first position, radiation generated by the emitter means is transmitted to and received by the detector means.

7. A switch as recited in Claim 1 wherein both the emitter means and the detector means are affixed to one of the elements such that when both the elements are in the aligned first position, radiation generated by the emitter means is reflected off the remaining element and received by the detector means.

8. A switch as recited in Claim 1 wherein the emitter means is a light emitting diode.

9. A switch as_.recited in Claim 1 or 8 wherein the detector means is a phototransistor.

10. A switch as recited in Claim 1 wherein the oscillating output from the generator means has a frequency on the order of ten kilohertz.

11. A switch as recited in Claim 1 wherein the oscillating output of the generator means is defined by square wave signal.

12. A switch as recited in Claim 1 wherein the logic circuit means further includes an indicator lamp having both an on and off condition to provide a visual indication corresponding to the first and second output signals of the logic circuit means respectively.