Abstract: An audible warning tone and a flashing optical signal are generated by a personal portable signalling apparatus when it detects the approach of a lighted moving vehicle. The flashing optical signal also alerts the operator of the moving vehicle of the presence of the user of the personal portable signalling apparatus. A housing is provided to optically isolate the receiving and transmitting portions of the optical apparatus.

Abstract: An apparatus for measuring an autocorrelation wavaeform of intensity of input light comprises a beam splitting means for dividing the input light into two light beams, a photoelectric converter for converting one of the divided beams into an electrical signal, an optical modulating means for modulating the other light beam in accordance with the electrical signal, a delay means for varying a relative delay time between arrival times to the optical modulating means of the light beam and the electrical signal, and a photodetector having a response speed faster than that of the delay time variation for detecting output light from the optical modulating means.

Abstract: A photodetector produces an output signal in response to irradiation by an optical beam from a pulsed laser. A delay unit delays the output signal for a period corresponding to one-half of one cycle of a beat frequency generated by interaction of two frequency components in the optical beam corresponding to two predetermined longitudinal modes of operation of the laser. A differential mixer subtractively combines the output of the photodetector with the output of the delay unit, to produce an output signal having the main profile of the laser pulses suppressed, and the beat frequency component, if present, amplified. A resonant circuit and amplifier may be provided to further amplify the beat frequency component. The output of the amplifier is integrated to produce a DC signal having a magnitude which corresponds to the amplitude of the beat frequency component. The DC signal is compared with a threshold value to discriminate between single and multimode operation of the laser.

Abstract: A pulse shaping circuit for use in a radiation detector. This circuit is adapted for x-ray spectroscopy. The pulse shaping circuit comprises a circuit for converting the output signal from the radiation detector into a step-function waveform, a pseudo-Gaussian filter consisting of a plurality of cascaded filter circuits, an adder circuit, and a gated integrator for integrating the output from the adder circuit. The adder circuit proportionally adds the outputs of each of the plurality of filter circuits in a predetermined manner and sums them up. The pulse shaping circuit achieves a high counting rate and a high resolution.

Abstract: In active range finder apparatus wherein an object to be inspected is illuminated by a laser source and light reflected by the object is detected in an imaging photosensor, a system is provided for increasing the dynamic range of the apparatus. This system provides for integrating over each of a series of measuring time periods light reflected from a window of the photosensor and hence proportional to the light received by such photosensor. When such integrated light exceeds a predetermined amount, a saturation signal is generated that immediately de-energizes the source. If this amount is not reached by the end of each period, the system is reset. The source is gradually re-energized at the commencement of each subsequent period. The virtually instantaneous de-energization and gradual re-energization combined with use of a saturation detector separate from the main photosensor ensures rapid action that is quick enough to substantially avoid saturation of such main photosensor.

Abstract: The quenching circuit comprises a signal comparator (CP) having a first input connected to the photodiode (SPAD) under control and a second input connected to a balancing impedance (C) equal to that of the photodiode. At the output of the comparator (CP) there is connected a signal generator (M), which generates a quenching signal (S) having a predetermined duration each time there is an imbalance between the two inputs of the comparator (CP). Circuital switching means (I1, I2, I3, I4) are provided, capable of holding the bias voltage of the photodiode normally high and of lowering it below the breakdown level following the generation and for the entire holding time of the quenching signal.

Abstract: A receiver circuit for receiving a modulated optical signal and for generating a corresponding electrical signal comprises a photodiode (1) for receiving the optical signal and for generating a first modulated electrical signal. An amplification circuit (3) receives the first electrical signal or a signal related thereto via an n stage (where n is an odd-integer) filter network (2) connected between the photodiode (1) and the amplification circuit (3). The output from the amplification circuit is fed to a first equalization amd noise filter (5). The characteristics of the filter network are such that the total thermal noise power output of the first noise filter is substantially minimized.

Abstract: In a semi-conducting integrated circuit, there is made a light detection circuit, the output signal of which can be used to counter manipulations by dishonest persons who undertake a decapsulation or a removal from the card when the integrated circuit is inserted in a bank type card, or even a depassivation of the upper protective layer of this integrated circuit, in order to reveal the secret functioning of the circuit or to modify its characteristics. The detector comprises a current generator delivering a current of limited intensity which flows into a reversed biased electronic junction. When the junction is subjected to light, the reverse current that can be allowed into the junction increases. Since the current generator is not capable of putting through stronger current, the voltage at the terminals of the junction drops. This drop in voltage is used as information that reveals the illumination.

Abstract: The invention relates to a voltage/frequency converter which contains a first and second change-over switch (13, 20). The first change-over switch supplies in its first position a measurement voltage and in its second position a reference voltage to a first input (15) of a comparison circuit (16). The second change-over switch supplies in its first position a first signal to be integrated and in its second position a second signal to be integrated via an integrator (22, 34) to the second input of the comparison circuit. The comparison circuit generates pulses dependent on the measurement voltage and sets the two change-over switches into their first position when the voltage supplied by the integrator is equal to the reference voltage, and into their second position when the value supplied by the integrator is equal to the measurement voltage. In this arrangement, one of the signals to be integrated is derived from the measurement voltage.

Abstract: An avalanche photodiode quenching circuit comprises a low value photodiode series resistor and a comparator amplifier. The comparator compares the photodiode potential with a reference voltage and changes state rapidly after initiation of a photodiode avalanche. The photodiode is actively quenched by taking its potential below breakdown. This achieved by a fast-switching transistor activated by avalanche detection at the comparator. A further fast-switching transistor is arranged to reset the comparator input after a preset delay following avalanche detection. The photodiode recharges passively through the series resistor at a rapid rate since this resistor has a low value. The quench and reset transistors are deactivated by comparator reset, the latter after the preset delay once more, and are isolated from the photodiode during recharge by diodes. The invention avoids the use of active photodiode reset pulses, and has constant output pulse width and well-defined dead-time.

Abstract: A photosensing system is described. Light rays to be sensed is incident on a photosensitive semiconductor device which allows much current to pass therethrough during receiving the incident light and which passes a little current when there is no incident light. The current passing through the semiconductor device is accumulated in a suitable storage means. The accumulated charge is detected, in order to judge the existence or the absence of the incident light, a certain time period after the pulsed signal is outputted.

Abstract: A motion detector has an infrared sensor for detecting a moving infrared energy source and for generating a current which charges a timing capacitor. The timing capacitor is commonly connected to the threshold and trigger input terminals of one timer in a conventional LM 556 dual timer package. The discharge output terminal of the timer is used for flowing current to a light source or other indicator device. When the timing capacitor voltage exceeds the threshold reference voltage, the discharge output pin is rendered conductive, and the indicator device is rendered active. When motion of the infrared energy source ceases, the timing capacitor is allowed to discharge, and, when the capacitor voltage falls below the trigger reference voltage, the discharge output terminal is rendered non-conductive. A photocell is coupled to the control voltage input terminal of the timer for varying the threshold and trigger reference voltage levels in response to ambient light.

Abstract: An alignment system for photoelectric switch includes a variable frequency oscillator producing a frequency which varies according to a light reception signal from a light receiving element in the photoelectric switch. A light emitting device is energized by the output of the variable frequency oscillator to give a visual indication of alignment. A threshold compares the amplitude of the light reception signal with a preset voltage. When the light reception signal exceeds the preset voltage, a logic element provide steady illumination of the light emitting device as an indication that alignment is completed. A lower threshold is then applied to the threshold to keep the light emitting device steadily illuminated until misalignment or propagation conditions reduce the amount of light received.

Abstract: A diagnosis apparatus for a photo coupler having at least one photo coupler including a light emitting element the amount of light emitted from which changes in accordance with the value of a current flowing therethrough and a light receiving element which receives the light from the light emitting element to convert it into an electric signal corresponding to the received amount of light, a checking current setting circuit for setting a current flowing through the light emitting element to a current value for checking, a level detecting circuit for controlling a current flowing through the light emitting element on the basis of the current value set by the checking current setting circuit, a reference signal generator for generating a reference signal, a comparing and detecting circuit for comparing the electric signal from the light receiving element with the reference signal and detecting the deterioration of a function of the photo coupler on the basis of the result of comparison.

Abstract: A photoelectric converting circuit including a light-receiving element which produces a current signal corresponding to the amount of light incident upon it and a current-to-voltage converting circuit which converts the current signal to a voltage signal. The circuit is characterized in that the current signal is supplied to the current-to-voltage converting circuit through an active circuit which exhibits a low input impedance. In preferred embodiments, the active circuit is a common-base transistor circuit in which an emitter current is supplied to the light-receiving element and a collector voltage is outputted as an output signal.

Abstract: A photo-electric converter according to the present invention has a switching element connected between a photosensitive element and a photo-electric converting circuit and another switching element connected in parallel with the photosensitive element, and an output from the photo-electric converting circuit obtained by turning on and off the switching element is analogue-to-digital converted and arithmetically processed. Thereby an offset voltage in the photo-electric converter circuit can be corrected and an accurate output can be obtained by the photo-electric conversion.

Abstract: An optical signal detecting circuit is configured so that its detection sensitivity for detecting an optical signal received by a light receiving element is set by selecting desired values of fixed current sources I and I' and a desired current division ratio of independent PNP multicollector transistors Q1 and Q2 and so that its optical signal detecting hysteresis range is set by selecting a desired current ratio of I and I' or a desired current division ratio of the independent PNP multicollector transistors Q1 and Q2.

Abstract: A method and apparatus for reducing noise in a light sensing circuit having a photodiode array coupled to a charge amplifier through a field effect transistor transfer switch. Thermal noise generated by the transfer switch is combined with image signals inputted to the charge amplifier resulting in an outputted noisy image signal. The invention eliminates this noise by taking two consecutive readings of the charge amplifier output, one before and one after closing the transfer switch and after opening it. The thermal noise generated by the transfer switch, and added to the next reading of the charge amplifier output, is equal to the difference between these two readings. Once stored, this difference can be subtracted from the previously mentioned "next reading", resulting in the elimination of this noise term.

Abstract: An electric current detector has a light source for generating light having substantially linear polarization and a predetermined polarization direction, a material substantially transparent to the light, the material having at least one characteristic direction, and the material exhibiting the Faraday effect in response to a magnetic field generated by the electric current. Also the light is launched into the material, and a predetermined angle established between the polarization direction and the characteristic direction, the predetermined angle chosen to permit separation of a rotation of the polarization of the light by the Faraday effect from polarization effects on the light by a birefringence of the material. A value of 22.5.degree. for the magnitude of the predetermined angle permits a separation of the rotation of the polarization due to the Faraday effect from polarization effects due to a birefringence of the material.

Abstract: A loss of optical input detector is disclosed disposed to receive a signal voltage from a fiber-optic receiver indicating that the optical input has dropped below a preset threshold. The detector includes a voltage follower connected to the fiber-optic receiver which passes to the detector circuit the signal voltage. A comparator circuit receives the signal voltage and compares it to a reference voltage. When the signal voltage is greater than the reference voltage the comparator produces and applies to an alarm circuit a positive voltage signal. This positive voltage signal turns on the alarm circuit. The alarm circuit provides a visual alarm indication and a logic signal to a controller interface indicating a loss of the optical input signal.

Abstract: A current-voltage converter circuit includes a current source outputting a current having a low-pass signal component and a high-pass signal component, a band splitter, a first converter, and a second converter. The band splitter splits the current output from the current source into the low-pass signal component and the high-pass signal component. the first converter converts the low-pass signal component split off by the band splitter into a first output signal having a first prescribed voltages. The second converter converts the output signal from the first converter and the high-pass signal component split off by the band splitter into a second output signal having a second prescribed voltage.

Abstract: The present invention is an apparatus for discriminating among various types of illuminants such as fluorescent light, tungsten light and natural daylight. The apparatus is comprised of an analog portion and a digital portion. The analog portion functions to convert incident light into a conditioned analog signal. The digital portion utilizes an analog-to-digital converter and a microprocessor to perform a Fourier series analysis on one or more of the harmonics of the illuminant signal. The microprocessor compares the amplitudes of the harmonics against the amplitudes of known illuminant sources to identify the source.

Abstract: A detection system including a radiation source and a radiation detector wherein the output of the radiation detector is positively fed back to the radiation source through a variable voltage/current controlling unit thereby providing a rapid and reliable detection signal on the current path for supplying a current to the radiation source. The variable voltage/current controlling unit may be, for example a parallel connection of a Zener diode or resistor and a bipolar junction transistor or FET controlled by the current output from the radiation detector. The radiation source part and the radiation detector part can be electrically connected to reduce the number of lead wires.

Abstract: A photoelectric amplifier comprising a photodiode having an anode connected to a gate of a first FET and a cathode connected to a gate of a second FET, with the second FET having a source-gate interconnection so as to be self-biasing. The photodiode cathode is connected to a high impedance feedback loop, including an output transistor, which is connected back to the photodiode anode. In a preferred embodiment, further included is a feedback circuit gain controlling transistor having a base driven by the feedback circuit and a current electrode connected to the source of the first FET.

Abstract: A method for reading a photosensitive element having a photodiode and a capacitor as applicable in particular to reading a low-level analog signals consists in introducing a biasing charge background, for example by means of calibrated uniform illumination prior to each read operation in order to cause forward biasing of the photodiode substantially beyond its knee voltage at the time of application of a control read pulse which reliably restores the voltage at the photodiode terminals to the knee voltage value, the current during the read operation being such that all the charges are then reliably transmitted via the capacitor to the integrating read amplifier.

Abstract: A source of light modulated by input data provides the modulated light to a phototransistor. A capacitor couples the emitter of the phototransistor to ground. A discharging transistor switch is coupled across the capacitor and a voltage comparator is coupled to the phototransistor emitter for providing a signal when the voltage across the capacitor exceeds a predetermined threshold. A microprocessor coupled to the comparator actuates the discharging switch in accordance with the comparator output.

Abstract: An improved optically bistable photodiode device comprises a photodiode in which the absorption of light is changed in accordance with a voltage to be applied thereacross, a circuit for amplifying photocurrent flowing through the photodiode, and a bias circuit for controlling the voltage to be applied across the photodiode wherein the incident light supplied to the photodiode is chosen to have a wavelength at which a resonance is produced in an exciton absorption or bandedge absorption where an electric field applied across a multiple quantum well is low so that a optically bistable operation is performed with a high speed response and low consuming power.

Abstract: Optical detector storage effects reduction is achieved by inserting an optical modulator between the optical signal to be measured and the optical detector. The modulator is normally turned off, and is only turned on during the period when the output of the optical detector is being sampled by a sampling system.

Abstract: An error detection system is provided for a two-state fiber optic sensor. An amplified photodetector signal is sampled by each of an ON-OFF threshold detector, a disconnect threshold detector and a slope detector. The ON-OFF threshold detector monitors whether the detector signal is above or below an ON-OFF threshold value corresponding to the parameter being sensed and activates an appropriate sensor output. The disconnect threshold detector monitors the constant low level detector signal corresponding to low level light received by the detector even when the thresold detector is in the OFF state, and triggers an error signal should the detector signal fall below a disconnect threshold value. The slope detector monitors the rate of change of the detector signal.

Abstract: A laser DC bias controller is disclosed for controlling and monitoring the laser of a fiber-optic transmitter. The arrangement comprises an optical power monitor including a light detector for converting the light output by the laser into photo current. The photo current is converted by the optical power monitor into a voltage representation of the magnitude of the light output by the laser. The voltage representation is output to a DC constant current source which uses the voltage to provide operating current to the laser of sufficient magnitude to keep the laser operating at a set output level. A transmit data detector monitors the incoming data signals to the fiber optic transmitter and outputs to the optical power monitor a current signal which indicates a failure of the data signal. The optical power monitor converts the current signal to a voltage representation which is output to the DC constant current source.

Abstract: A light detector measures the intensity of two different light beams, computes a ratio of an AC to a DC component for each light beam, and computes a quotient by dividing a first of the above ratios by a second of the above ratios. A light detector has a first photodetector, means, responsive to the first photodetector, for computing a first ratio of an AC component to a DC component of the intensity of a first light detected by the first photodetector, means for producing a first average value of the first ratio, a second photodetector, means, responsive to the second photodetector, for computing a second ratio of an AC component to a DC component of the intensity of the second light detected by the second photodetector, means for producing a second average value of the second ratio, and means for computing a quotient by dividing the first average value of the first ratio by the second average value of the second ratio.

Abstract: This invention relates to a detection circuit for use in a servo controlled fiber optic sensor. A low noise signal with an amplitude proportional to the magnitude of the synchronous detection output is produced without the use of filter by a calculation of the average vale of the synchronous detector output signal driving one complete cycle of the dither signal cycle. This value is fed into sample and hold circuitry, which in turn controls the series motor.

Abstract: An optical power meter system comprises a chopper with a semicircular total reflection mirror along an incident light path, two photo-detectors of different characteristics of wavelength sensitivity, and a comparator for comparing the levels of the photo-detection signals derived from the two photo-detectors and for outputting the optical detection signal of a higher level. The photo-detectors are positioned in a first path of the light passing through the chopper and a second path of the light reflected by the chopper, respectively. The comparator may be replaced by an adder for adding the photo-detection signals derived from the two photo-detectors.

Abstract: A semiconductor light detecting integrated circuit comprises a light detecting element, a constant current source having a first FET connected in series to the light detecting element and a power source, the constant current source having a region in which a constant current flows through the first FET, and an electrical circuit having a second FET the gate of which is connected to a connecting point between the light detecting element and the constant current source, the electrical circuit providing a two-valued output for the gate voltage at the connecting point generated according to whether or not the output current of the light detecting element reaches a predetermined current set in the constant current region of the constant current source.

Abstract: A photo sensor circuit including an LED (12) and a phototransistor (14) coupled together by resistors (R.sub.1, R.sub.2) and connected to a drive and sense network (16) including resistors (R.sub.B, R.sub.3, R.sub.4), a source of positive voltage (+Vcc) and a PNP transistor (20) by a single conductor wire (W.sub.1). When the light path between the LED (12) and the phototransistor (14) is blocked, the circuit standby current is low and the transistor (20) is OFF, but when the light blockage is removed, the increase in current through the LED (12), triggered by an increase in current through the phototransistor (14) quickly drives the transistor (20) into saturation. The phototransistor (14) will keep full current flowing through the LED (12) as long as the light blockage is removed.

Abstract: A light pulse detecting device having a photo-transistor whose output is compared with a level to detect incidence of a light pulse thereon. In this device, the photo-transistor is provided with other transistors cascode-connected thereto. For this reason, the capacitance of the emitter-collector path of the photo-transistor becomes equivalently smaller, improving the response characteristic of the light pulse detecting device.

Abstract: A light sensitive switching circuit for automatically controlling the supply of electric power from a power source to a load, such as a lantern, is disclosed. When it becomes darker than a predetermined brightness the power supply starts and when it becomes bright again, the power supply is cut. The light sensitive switching circuit comprises first and second lines for connecting the power source and the load in series between the first and second lines. A first thyristor is connected between the first and second lines, and a second thyristor connected is to the first thyristor such that the anode of the second thyristor is connected to the gate of the first thyristor and the cathode of the second thyristor is connected to the cathode of the first thyristor. A photocell is connected between the gate and the cathode of the second thyristor.

Abstract: An improved optical endpoint detector is disclosed in which two photocells are used in conjunction with analog multipliers and variable voltage sources, all under microprocessor control. The combination enables one to measure the ratio of intensity of different emission lines, as well as their individual outputs and alternative process monitoring signals.

Abstract: A controller controlling the dispensing of paper currency including a microprocessor for controlling motors which feed a predetermined mix of paper currency from each dispensing device to a common acceleration device which advances bills to an output stacker. Each individual dispensing device dispenses the proper number of bills to the acceleration device. Apparatus multiplexes the control signals to the stepper motor. After the bills have been dispensed, the stepper motor is halted, and a home positioning sensor determines if the stepper motor has been halted in the proper position. Sensors provided at spaced intervals along the common acceleration device determine if bills have reached the acceleration device. The dispensing operation is repeated if bills do not reach the sensor. The sensors perform the dual function of sensing advancement of a bill and detecting overlapping or multiple fed bills. The adaptive technique conmpensates for changes in the sensor such as component aging and dust accumulation.

Abstract: A device for stabilizing an output of a photosensor which uses a light-emitting element and a light-receiving element is disclosed. A resistor is connected in series with the light-emitting element to control a voltage across the series connection of the light-emitting element and resistor to a constant value. The output of the light-receiving element is stabilized against temperature variations without resorting to an extra light-receiving element for compensation.

Abstract: The device includes an audio signal circuit having two separate terminals that are connected through the photoresistor elements of two, separate, optical isolators with an audio signal input/output terminal, so that signals can be routed selectively and bidirectionally along separate signal paths to or from the input/output terminal to one or both of the two separate terminals. A separate control circuit supplies DC power selectively to the LED's which control the selective energization of the photoresistor elements of the optical isolators, the advantage being that the photoresistive devices permit selective blocking of the audio signal paths without physically opening or interrupting the paths and thus avoiding objectionable signal spikes and consequent loud popping sounds in associated loud speaker systems. The DC control circuit includes two, manually operable double pole, double throw switches for controlling the selective routing of signals between the audio signal terminals.

Abstract: A circuit containing a photodiode for determining when there is sufficient illumination for an optical device to operate having provision for compensating signal variations due to temperature-dependent operation of the photodiode by supplying logarithmic means with an input from a potentiometer connected to a temperature-dependent distributor circuit.

Abstract: A signal processing apparatus for a semiconductor position sensing device has an impedance element connected to one output terminal thereof. When a distance to an object is to be detected, an impedance of the impedance element is varied until the outputs of the sensing device substantially balance. The distance to the object is determined by the impedance of the impedance element when the outputs balance.

Abstract: A toy having an optically actuated sound generator includes first and second phototransistors coupled in series for creating a substantially binary output voltage based on the relative light intensities striking such phototransistors. A Schmitt-trigger circuit receives the binary output voltage and eliminates therefrom light-flicker components resulting from fluorescent lighting. Additional circuitry creates an enabling pulse at each transition of the Schmitt-trigger output signal, which enabling signal enables dual oscillator circuits. The dual oscillator output signals are gated together to drive a speaker for creating audible signals and to activate a light emitting diode. The electronic circuitry and speaker are housed in a baffle through which the phototransistors and light emitting diode protrude for communicating with a face portion of the toy.

Abstract: A noise-generating toy includes first and second optical sensors to detect the intensity of light in first and second optical fields, respectively. The sensor signals serve as inputs to a comparator which provides as an output a differential signal indicative of the difference between the sensor outputs. The comparator output drives an oscillator which generates audio signals in response to the differential in the intensity of light. The oscillator drives one or more speakers with the audio signals, and the speakers use the audio signals to produce audible sound or noise.

Abstract: A photoelectric control device having a photoelectric sensing unit for delivering an output voltage in response to changes of the intensity of light, the output voltage being applied to a capacitor for operating a SCR. When the output voltage reaches a predetermined level the SCR is caused to become conductive or non-conductive. The SCR is connected to a bridge rectifier which causes a triac to become conductive or non-conductive when the SCR becomes conductive or non-conductive, so as to allow electric power to be supplied to a load or to be cut off in response to changes in the intensity of light.

Abstract: A photoelectric type displacement detecting apparatus, such as a digital display dial gauge micrometer, with an improved frequency response, comprising optical lattice means, light emitting means for irradiating the optical lattice means with a detecting light, light receiving means for receiving a transmission or reflective light from the optical lattice means, and a detection circuit for generating an output signal indicative of relative movement in the lattice. The frequency characteristic of a phototransistor adapted in the light receiving means depends on the input impedance of a base-grounded transistor to maintain the current supplied to the light emitting means constant and to improve the frequency response in the detection apparatus.

Abstract: An optical sensor arrangement comprises a light-emitting diode which is connected to a light detector over a light connection such as a fiber optics fiber. The fiber may be provided in the vicinity of a vortex shedding flow meter and is bent by the passage of vortices past the fiber. Bending the fiber causes attenuation of the light signal from the light-emitting diode to the light detector. The light-emitting diode is powered by a pulse generator which supplies the diode with low duty cycle high-current pulses. The resulting detected pulses are amplified, sampled and held to obtain peak values for each pulse. The detected pulse is suppressed by a feedback circuit portion which is activated only after each low duty cycle high current pulse. The detected peaks are utilized to generate a square wave which is used as a measurement of the variable, in particular the passage of vortices in a vortex shedding flow meter.

Abstract: The detector comprises an avalanche photodiode for receiving a light beam, a circuit for measuring the mean current across the avalanche photodiode and a bias voltage source. That source is controlled by the circuit for applying to the photodiode a bias voltage such that the mean current across the diode be substantially equal to an adjustable set value.

Abstract: Sensors in the infeed and output stackers, under control of the microprocessor, monitor the sheets. The apparatus is started automatically by placing sheets in the infeed. A count of the sheets is developed and displayed as the sheets are fed. When the infeed is empty and the output contains sheets, the count is retained. If sheets are removed from the outfeed, the count is retained and is reset only after more sheets are placed in the input. The same rules obtain for batching. The sensors cooperate with singles, holes and doubles detectors and have their gain adjusted depending upon sheet density. Automatic threshold adjustment circuits compensate for dust build-up and component aging. Upon sheet detection, the sensing circuit threshold level is instantaneously shifted to prevent an abrupt change in intensity from the sheet covering the sensor to provide an erroneous indication of the presence of a subsequent sheet or sheets.