Abstract: An opto-electronic end-of-tape sensor has a pulsed light source for producing high intensity, short duration light pulses and a photodetector controlling a clock driven digital counter. In a normal condition with tape blocking the light pulses, the counter is kept in a reset state. If a clear light path of sufficient time duration is detected the photodetector output enables the counter to reach a predetermined count to obtain an end-of-tape signal output. The sensor circuit discriminates against pinholes in the tape by requiring detection of an uninterrupted predetermined number of light pulses to generate the end-of-tape signal.

Abstract: A three-mode analog controller for regulating a signal corresponding to a controller variable to produce a controller output, comprises an integrating circuit, a proportional circuit, and a derivative circuit. The integrating circuit includes a reset adjustment for varying a time constant thereof, the proportional circuit includes a gain adjustment for varying the gain thereof and the derivative circuit includes a rate adjustment for adjusting the rate of derivation of the signal. The gain adjustment comprises a photoresistor associated with a source of light which is provided with varying current corresponding to the signal to vary the resistance of the photoresistor and, thus, the gain value. The reset and rate adjustments may also comprise photoresistors with light sources or may be formed of field affect transistors each controlled by a circuit and remotely located potentiometer or variable voltage source.

Abstract: An optical proximity detector of very small size and high resolution is provided by using a light emitting diode (LED) to illuminate a small detection region adjacent to the LED and by using the same LED simultaneously to sense light reflected from an object which enters the detection region. A circuit is provided which continuously forward biases a light emitting diode at a substantially constant bias current, thereby continuously illuminating a small region adjacent to the diode. When an object enters the illuminated region and reflects light back to the LED, it has been found that the impedance of the LED changes by a small amount. This small change in LED impedance and consequently the presence of a light reflecting object in the illuminated region is sensed by the circuit.

Abstract: A voltage detecting circuit includes an input circuit section including a light emitting diode and a current supplying circuit for supplying a current to this light emitting diode in response to an input voltage, and an output circuit section for generating an output voltage in response to the light emitted from the light emitting diode. This output circuit section includes a phototransistor which, together with the light emitting diode constitutes a photocoupler. A characteristic between the input voltage and the output current of the current supplying circuit represents a hysteresis characteristic.

Abstract: A pickup level control device for a system for reading out recorded information which has a pickup element producing a pickup output signal. The device detects a dc component of the pickup output signal and produces a level control signal. A voltage level of the pickup output signal is controlled in response to the level control signal produced by the dc level detection operation. The control of the voltage level of the pickup output signal is performed by a variable impedance element connected to a terminal of the pickup element, so that a peak level of an ac component of the pickup output signal is controlled below a predetermined level.

Abstract: A measuring circuit for measuring the light intensity received by a photosensor comprises a photosensor which generates photocurrent proportional to the intensity of received light, an integration circuit for integrating the photocurrent generated and for measuring the intensity of light by measuring the time period from the start of integration until the integrated value reaches a predetermined level. In order to provide a wider dynamic output range, a signal generator which produces a monotonously changing voltage signal is connected to add its signal to the integrated signal.

Abstract: An alternating bias is applied to a modified photoconductive detector and photosignal extracted from each detector element. This extraction may be performed using an integrator to produce a dc signal output, or alternatively by using a high-pass filter or phase-sensitive detector to extract a photosignal at an harmonic of the bias frequency. The detector used is provided with elements that have a responsivity that is a different function of bias amplitude for each polarity. The detector element may be shaped with variation in width or depth, to produce this differential responsivity. Alternatively element bias contacts may be of different width to produce field gradient and differential responsivity. It is advantageous to obscure a part of each element area by including an opaque mask.

Abstract: A chemical analysis system for analyzing a plurality of independent specimens that have time varying characteristics includes a circumferential array of analysis regions that hold the specimens. The analytical regions are sequentially and repetitively sensed and resulting analysis signals corresponding to monitored specimen characteristics are stored in corresponding memory locations. A signal transmission channel connected between the sensor and the memory includes a signal storage capacitor and variable slew rate circuitry.

Abstract: A photo transducer circuit (30) selectively controls the current which is transmitted between power terminals (32, 34). A light emitter (20) transmits light to a first photo receiver (24) and a second photo receiver (26). A vane (16) is movable by a Bourdon tube (12) to permit a variable amount of light to pass from the photo emitter (20) to the photo receiver (26). The output of the photo emitter (20) is regulated by a circuit which monitors the output of the photo receiver (24). Circuitry is provided to set a minimum current flow between the power terminals (32, 34) when the vane (16) substantially blocks illumination of the photo receiver (26). Further circuitry is provided to set a maximum current flow between the power terminals (32, 34) when the vane (16) allows substantial exposure of the photo receiver (26) to the light produced by emitter (20).

Abstract: It is a problem extracting the photosignal component from detector output, to the exclusion of pedestal bias response. To overcome this, a time varying bias signal is applied to each element of the detector. The duration of the time varying bias signal, or if a periodic signal, the signal period, is chosen as long compared to photocarrier lifetime and the signal amplitude is large enough to range over a non-linear portion of the responsivity characteristic of each element. The bias signal contains a d.c. component so that the bias signal ranges about a point of operation--a point of asymmetry lying on the responsivity characteristic. The photosignal component of the output signal may be removed by time averaging or by harmonic separation. Alternatively the bias signal may be modulated, and the photosignal component extracted by detection of demodulated signal.

Abstract: An optical receiver for responding to optical energy propagating in an optical fibre transmissions path (1) is detected by a reverse-biassed p-i-n diode (2) which is in series with a forward-biassed p-i-n diode (3). The junction between the two diodes is connected to the input of an amplifier (4), which feeds on auto-equalizer.The auto-equalizer includes another p-i-n diode (7) which is in series with the signal path, and is forward-biassed. Due to the associated components including resistors (9,10), the diode (7) passes the same average current as do the diodes (2,3) at the front end of the receiver. The overall effect of the third diode (7) is to provide the receiver with a substantial region in its characteristic whose frequency response is flat.

Abstract: Pulsed light barrier apparatus is driven directly from an a.c. supply voltage connected to the terminals L and M with the terminal M being earthed. A storage capacitor 14 is charged during the positive half wave of the a.c. supply voltage and is discharged at a time determined by a programmable unijunction transistor 13 through a photodiode 11 to emit a flash of light which passes across a region monitored by the light barrier to a photoreceiver 26. A Zener diode limits the voltage across the storage capacitor 14 to a value less than the peak a.c. supply voltage. As soon as the voltage across the storage capacitor has reached the Zener breakdown voltage the excess energy from the a.c. supply voltage is directed through a rectifier diode 18 to a smoothing capacitor 19 where it forms a positive operating voltage for the light receiver arrangement. During the negative half wave of the a.c.

Abstract: An avalanche photo-diode bias circuit compensates for temperature variations in the breakdown voltage by controlling the bias voltage so that the ratio of the bias voltage to the breakdown voltage remains constant, to achieve a constant current amplification factor.

Abstract: An optical receiver, for responding to optical energy propagating in an optical fibre transmission path (2) is detected by a reverse-biassed p-i-n diode (3) which is connected in series with a forward-biassed p-i-n diode (7). The junction between the two diodes is connected to the input of an amplifier (5), which is part of a two-stage amplifier (5,8), with automatic equalization (9,10,11).The forward biassed diode, by its characteristics leads to an improved dynamic range for the receiver as compared with conventional optical receivers.

Abstract: A switching apparatus for an absolute position measuring device of the type including a coded scale and a scanning unit for reading the coded scale, wherein the scanning unit includes a plurality of electrical components. The disclosed switching apparatus includes a capacitor connected in parallel with the electrical components and a switching element, such as a transistor, connected in series with the electrical components and in parallel with the capacitor. The switching element is responsive to a switching signal to selectively apply a supply voltage to and interrupt the supply voltage from the electrical components, all without charging or discharging the capacitor.

Abstract: A chemical analysis system for analyzing a plurality of independent specimens that have time varying characteristics includes a circumferential array of analysis regions that hold the specimens. The analytical regions are sequentially and repetitively sensed and resulting analysis signals corresponding to monitored specimen characteristics are stored in corresponding memory locations. A signal transmission channel connected between the sensor and the memory includes a signal storage capacitor and variable slew rate circuitry.

Abstract: An exposure indicator for photographic plate makers including a comparator having a control input, an inverting input and an output; a light emitting diode having its anode connected to the control input for developing a reverse bias signal at said control input in response to illumination from the plate maker light source whereby an output comparator signal is generated when the control input signal exceeds a reference signal at the comparator's inverting input; the output signal forward biasing the light emitting diode to its light emitting state and also fed back to the control input to maintain the light emitting diode in such emitting state; and vacuum operated switch means to provide power to the indicator circuit in response to vacuum actuation of the plate maker flexible blanket.

Abstract: An improved high speed optical receiver provides an output that accurately corresponds to the optical input signal without the distorted signals caused by ac or dc coupled receivers when exposed to signals having varying amplitudes. Delaying and dividing circuits permit the creation of threshold signals which eliminate the drawbacks previously encountered.

Abstract: In a radiant energy beam scanning system, a detector, positioned at a predetermined position along the path scanned by the beam, for sensing the center position of the power distribution within the beam and generating a signal indicative thereof. When utilized in an information recording system, the detector is positioned adjacent the start position of the scan path so that the generated indicator signal provides a reference for system timing and synchronization. In such a recording environment, synchronization of the system relative to the center position of power distribution within the beam compensates for variations in beam power level and focus, assuring proper alignment of information recorded on consecutive scan lines. In a preferred form, a diode detector, partially masked in a cross-scan direction, is employed to provide an output signal when irradiated by the scanning beam.

Abstract: A digital photoelectric angle or length measuring instrument, of the type having a scale with at least one division, a scanning unit for scanning the division to generate a scanning signal, and an evaluating unit having a trigger circuit for evaluating the scanning signal, is provided with means for generating at least one test signal and means for selectively applying the test signal either to the trigger circuit or to a light source such that the trigger threshold of the trigger circuit is temporarily varied by a selected amount, thereby providing a simple, reliable check of the trigger threshold of the trigger circuit, without requiring external equipment or disassembly of the measuring instrument.

Abstract: An optical type detector comprises a full-wave rectifier circuit to which input power source voltage arbitrarily selected is supplied, a switching regulator, a detecting section supplied with power from the switching regulator and optically detecting an object to output a detection signal, and a relay switch for performing switching operation in response to detection signal and producing a detection output corresponding to detection signal. The switching regulator includes a drive section which has two transistors connected in series with each other. When the input power voltage is applied, the two transistors divide the power voltage into substantially equal two parts.

Abstract: A method and apparatus for binary coding of sensor signals received from a number of optoelectronic sensor elements employ an evaluator associated with each sensor element for generating binary output signals corresponding to the amount of charge generated by the associated sensor element. Selected pairs of evaluators are connected to an electronic switch, with one of the evaluator outputs serving to actuate the switch for the purpose of undertaking a charge quantity comparison between the associated sensors which are disposed a small distance from one another. Each evaluator includes a converter consisting of a switching transistor and a load element connected in series, and a barrier transistor connecting the output of the associated sensor element with the input of the converter, and a reset transistor for connecting the converter input with a constant voltage source.

Abstract: The output (18) from an optical sensor is recharged for a time dictated by the output of the digital-to-analog converter (11). A previous count indicative of the recharge time is stored in memory (52) which controls the converter (11). This count is manipulated in incrementing circuit elements (54) (70 and 72) depending on the time the comparator (12) signals a difference signal, indicative of a period of recharge.

Abstract: There is provided a photoelectric switch comprising a photoelectric detection means, a circuit means disposed independently of the detection means, and cable means interconnecting the detection and circuit means, there being formed in the photoelectric detection means a parallel circuit comprised of a light emission photodiode and a display photodiode of opposite polarity thereto as connected in parallel-circuit relation, which parallel circuit is connected to a pulse oscillation circuit included in the circuit means with a couple of lines, whereby a pulse current of single polarity is applied from the pulse oscillation circuit to the parallel circuit to thereby actuate only the light emission photodiode, and there being disposed in the circuit means a display circuit which functions in response to a detection output obtained in the circuit means so that through the tow lines a pulse current of opposite polarity to the first-mentioned pulse current flows to the parallel circuit in a phase where the first-ment

Abstract: There is provided a photoelectric switch comprising a light projecting segment including a pulse oscillator and a light-emitting element adapted to give a pulse light emission in response to an output pulse of the pulse oscillator, a light reception segment including a light reception element adapted to yield a light reception signal on incidence of light, a gate circuit adapted to gate the light reception signal according to the output pulse of the pulse oscillator and an integration circuit for integrating outputs of the gate circuit, and a control circuit for varying the pulse frequency by controlling the pulse oscillator on generation of a light reception signal from the light reception element.

Abstract: The optoelectronic switch includes a photosensitive GaAs FET onto which an optical signal may be directed. The optical signal is derived from an RF modulated light source. A voltage circuit is connected to the FET to switch the FET "on" or "off" by placing a positive or zero voltage respectively on the drain. An isolation of over 70 dB is obtained in this FET switch.

Abstract: A photoelectric scanner system includes photosensors (10), an amplifier (15), and a demodulator (17), and functions to produce an output signal indicative of when light signals of a predetermined intensity are being received by the photosensors. An alignment indicator control circuit (20) is connected to receive the amplified light intensity signals, and functions to produce a repetitive alignment indicating signal whose frequency is generally proportional to the intensity of the received light signal. The signals are applied to an alignment indicator which, in the preferred embodiment, is a light emitting diode, so that the LED flashes at a frequency indicative of the degree of alignment of the system, enabling an operator to accurately align the photoelectric scanning system with reference to the flash rate of the alignment indicator.

Abstract: Apparatus for performing tests for determining the validity of a paper purported to be a valid instrument is presented. Fundamentally, the invention comprises a tray for receiving a paper offered as a valid instrument and maintaining the same in sliding relationship between a light source and reticle. A photocell is operatively connected to the reticle and senses light passing from the light source and through the paper and reticle. The output of the photocell is applied to an operational amplifier having a dynamic feedback network and the output of this amplifier is characteristic of both a grid pattern upon the paper and the optical density thereof. This output is then passed to an amplifier circuit which establishes an optical density domain and is operative to pass a signal only if the paper falls within such domain. This output is then passed to appropriate integrating and comparator circuitry to ultimately determine the validity of the paper.

Abstract: An automatic bandwidth control system for an adaptive optics servo utilizing an adjustable amplitude low frequency sinusoidal dither signal to optimize the servo bandwidth for a particular target scenario thereby minimizing bandwidth-related degradation.

Abstract: An analog-digital converter is disclosed which monitors an output signal of an optoelectronic sensor element for the attainment or non-attainment of a reference charge, whereupon switchover occurs from one logic signal to the other. An exclusion to a large extent of parameter or characteristic tolerance effects on the result of the evaluation is achieved. For this purpose, the converter contains an inverter, the input of which is connected via a reset transistor with a constant voltage source and which is connected via a potential barrier defining transistor with the output of the sensor element. The converter shows no dependence upon fluctuations of the inverter. Applications include distance measuring devices, and photographic and electronic cameras.

Abstract: An electron multiplier, including an excitation means and collector, disposed in a high vacuum chamber and adapted to be coupled at its input to a charged particle analyzer is coupled through the vacuum chamber wall by a plurality of electrical feedthrough devices such that the excitation means is coupled to a high voltage power supply disposed outside the high vacuum chamber and the collector is coupled simultaneously through a capacitance coupling means and a resistance coupling means, both disposed within the high vacuum chamber, to an amplifier-discriminator and floating operational amplifier, respectively, both disposed outside the high vacuum chamber. The impedance offered by the capacitance coupling means is substantially lower than that offered by the resistance coupling to 10 nanosecond current pulses originating from single electron events.

Abstract: A liquid presence detector having a light-transmissive chamber for the liquid to be detected. A light emitting diode is positioned outside of the chamber for transmitting light through the chamber and a photosensitive transistor is positioned for receiving the light that has been transmitted through the chamber. The light emitting diode is located at a distance from the chamber that is equal to the focal point of a lens that is created by the chamber and liquid when the liquid is present. The photosensitive transistor output voltage is compared with a reference voltage and an output signal is provided in response to a predetermined difference between the detector output voltage and the reference voltage.

Abstract: The invention is directed to an instrument control apparatus capable of regulating the flow of electric current by detecting relative movement between an indicator and a control zone. A light source is positioned close to the control zone so that illumination from the control zone will change responsive to movement of the indicator. Illumination from the control zone is sensed and electrical resistance is varied in response to relative movement between the indicator and control zone for varying an output voltage. A first predetermined reference voltage is generated and the output and reference voltages are compared and a first predetermined output current is generated when one of the voltages is greater than the other one. A first circuit supplies electric current to the instrument.

Abstract: Photo-electric detector comprising a multivibrator with two complementary transistors (T.sub.3 and T.sub.4) of which the base of the first is coupled to the collector of the second by a time constant circuit (R.sub.5 -R.sub.6 -C.sub.1) comprising a resistance (R.sub.5) with negative temperature coefficient. This multivibrator excites an electro-luminescent diode (D.sub.1) which cooperates with a photo-transistor (T.sub.1). After integration, the received signals control a commutator (thyristors Th.sub.1 and Th.sub.2). The circuit is fed by a rectifier bridge with diodes (D.sub.11 to D.sub.14) and formed with two wires.Application to the detection of the presence of an object which blocks the luminous beam emitted by the diode (D.sub.1).

Abstract: Apparatus for automatically detecting and measuring the energy of laser pes over a wide range of energy levels and in the presence of high ambient light levels. The current produced by a laser pulse striking a photoconductive detector is integrated by a capacitor to obtain a voltage across the capacitor which is proportional to the total energy incident on the detector during the pulse. The total energy of the pulse is then determined by measuring the time from when the capacitor voltage crosses a reference level during current integration to the time when the capacitor voltage, discharging through a resistor recrosses the reference voltage. The leading edge of the capacitor charging voltage is used to couple a high frequency oscillator to the input of a counter. The oscillator is then decoupled from the counter when the voltage of the discharging capacitor crosses a reference level. The count in the counter is transferred to a shift register for transmission to a data processing device.

Abstract: Monolithically integrable semiconductor circuit with an amplifier controlled by a photo diode, including a differential amplifier having inverting and noninverting inputs and outputs and a photo diode having a first and a second lead, the first lead of the photo diode being connected in the blocking direction to the inverting input of the differential amplifier, and the noninverting input of the differential amplifier being connected to a reference potential, a coupling resistor connected between the inverting and noninverting inputs of the differential amplifier, a filter circuit and a transistor amplifier being connected in a feedback branch between the noninverting output and the inverting input of the differential amplifier, and the inverting output of the differential amplifier and the second lead of the photo diode being connected to ground.

Abstract: A radiant energy system includes an energy receiving member for receiving energy and for converting received energy into electrical signals. Current amplifying means are coupled to the radiant energy receiving member. Voltage comparator means are coupled to the current amplifying means to compare the voltage developed by the current amplifying means to a reference voltage. The comparator provides an output signal indicative of whether the voltage applied to the comparator input is sufficient to actuate the circuit. The output characteristics of the comparator can be selected to be consistent with TTL and data processing circuit drive requirements. The system is suitable for use wherein the radiant energy devices are employed as position indicators for moveable parts and or electrical isolation of postage meters.

Abstract: Electrical monitoring and/or control circuit including a high impedance transducer--for example a photo-diode--which is situated remotely from a measuring circuit and linked to it by a balanced twisted pair of wires fed by a power MOSFET forming a "buffer". The arrangement is such that equal pulses of opposite phase are induced in the twin feeder when a pulse output is produced by the transducer, which is substantially noise-immune without the use of coaxial cable and without the necessity for situating all the measuring circuitry at the transducer position. May be used in "difficult" electrical environments, e.g. where there are electric motors such as in tobacco-feeding arrangements.

Abstract: A chromosome detector using a scanning microscope system is used to detect the presence of a chromosome spread in a slide specimen and to produce a signal usable by the scanning microscope system to automatically operate the microscope system whereby the detected chromosomes are centered in the field of view, are automatically focused and their location converted to coordinate data which is stored in a memory system whereby the system may be used to re-examine the detected chromosome by the use of the stored X-Y coordinates. The detector performs an amplitude and frequency analysis of a cell find signal produced by a slide scanner in the scanning microscope system and produces, in turn, an output signal representative of a detected chromosome spread and compatible with the scanning microscope control circuit.

Abstract: A two-terminal optical sensor circuit comprising a light-emitting diode, phototransistor, amplifier, and current source electrically and optically coupled so as to approximate an ideal switch in one quadrant of its V-I characteristic. A remote object is detected when it moves into the optical path between the light source and sensor.

Abstract: An opto-electronic detector has a radiation-emitting element and a radiation receiving element which are linked optically and also by an electronic circuit so that the radiation-emitting element is caused to produce radiation pulses due to feedback between the radiation-emitting and receiving elements.The construction of the electronic circuit is such that sharp pulses are produced having an amplitude and frequency dependent on the optical feedback factor, and such that the pulses are spaced by intervals in which the radiation-emitting element is entirely extinguished.The electronic circuit comprises a current amplifier (T2) which feeds the radiation-emitting element (D1). This amplifier is controlled by the radiation-receiving element (T1) and by a filter (R1C1) which incorporates a storage element such as a capacitor.

Abstract: A light-responsive control circuit for the purpose of connecting a load, generally an electric lamp, to an AC source every evening at dusk and disconnecting the load from the AC source later each night at a solar time established by the setting of timepiece-like controls, all without the need for user synchronization of included timekeeping circuitry with the time of day. Starting at dawn each day, a light-responsive switch causes a counter to measure the passage of time by accumulating a count representing one-half hour for each hour that passes, by counting alternations of the AC source voltage. At dusk the count approximately represents the number of hours that have elapsed since solar noon and at that time the light-responsive switch causes the load to be switched on and also causes a signal having a frequency double that of the AC source voltage to be applied to the counter to maintain a correct representation of the solar time of day.

Abstract: A system (10) for optimizing the gain of an avalanche photodiode (12) and an associated avalanche photodiode preamplifier (14) includes a variable voltage power supply (58) interconnected to the avalanche photodiode (12) for providing a bias voltage source for the avalanche photodiode (12). Circuitry (26, 28) is provided for measuring the output noise level of the avalanche photodiode (12) and preamplifier (14). Additional circuitry (46, 48) is responsive to the circuitry (26, 28) for measuring the output noise level of the avalance photodiode preamplifier (14) for generating a control signal.

Abstract: The present invention is a light receiving circuit which includes an active device and light responsive switching device. The active device has an emitter, a base and a collector, the base being responsive to a first constant voltage source and the collector being responsive to a second voltage source. The light responsive switching device has a first lead and a second lead, the first lead being connected electrical ground and the second lead being connected to the emitter of the active device. The light receiving circuit of the present invention exhibits a high response speed and a stable output waveform. In another embodiment, the light receiving circuit of the present invention includes two active devices and two light responsive switching devices.

Abstract: An improved input circuit is provided for an array of photo detectors. For each photo detector in the array, the circuit utilizes a first FET with a source for coupling to an output of a photo detector, a gate coupled to a first gate voltage, and a drain for coupling to an output circuit. The first gate voltage is provided by a feedback circuit which utilizes matched properties of adjacent FETs. In one embodiment, FETs are used in an open loop feedback circuit to reduce the input impedance seen by the photodiode at the source of the first FET. A similar objective is accomplished in another embodiment utilizing FETs in a closed loop feedback circuit. Further embodiments utilize FETs arranged as a differential amplifier with active loads to provide a low input impedance and a virtual ground at the source of the first FET.

Abstract: A novel photodetector circuit utilizing both the generated photovoltage, as well as its inverse, to improve the signal-to-noise ratio at the optical receiver output.

Abstract: Illumination control apparatus for supplementing light from solar radiation with light from an artificial light source to compensate for periods of insufficient levels of solar light to maintain a desired illumination level within an interior space comprising an artificial light source connected to an electrical power source with switch means for selectively energizing said light source, actuator means for controlling the on-off operation of the switch means, a light sensor connected to the actuator means for controlling the actuator means in response to the illumination level of the interior space, and a limit switch carried adjacent the actuator for limiting the movement of the actuator within a predetermined range so as to prevent further movement thereof during detection of erroneous illumination conditions.

Abstract: A leak current suppressing printed circuit board in which the input circuit is so designed that between the input terminals a light sensing photoelectric converting element operating in the current mode is connected. The input is guarded by means of the circuit net, whose potential is same as that at the input terminal of the inverting input circuit or the non-inverting input circuit of the high input impedance operation amplifier.

Abstract: Disclosed is a control circuit used to conserve power in a portable optical recognition system. When the system is not being used or between actual scans of the reading electronics, power is supplied only to those circuits required to control power to the system and to permit sequence reading of items. An infrared signal is emitted from the reading device and when a document or other item to be read is scanned the infrared signal is reflected back into the scan unit and is detected, thereby sensing that a document is being read and turning the system on.

Abstract: A leak current suppressing printed circuit board in which the input circuit is so designed that between the input terminals a light sensing photoelectric converting element operating in the current mode is connected. The input is guarded by means of the circuit net, whose potential is same as that at the input terminal of the inverting input circuit or the non-inverting input circuit of the high input impedance operation amplifier.