Abstract: A voltage controlled oscillator (VCO) having high temperature stability and wide voltage/frequency linearity is provided. The VCO comprises a multivibrator being switched by a bipolar type device, and temperature fluctuations of the bipolar type means are compensated by a FET current source coupled thereto. To provide a linear relationship of frequency vs. voltage over wide voltage range, the bipolar device is further regulated by a plurality of resistor and diode networks.

Abstract: A variable frequency oscillator (VFO) providing a plurality of timing signals set by an external resistor is described. The single external resistor is utilized to set the center frequency of the VFO. The VFO is comprised of a voltage controlled oscillator (VCO), analog divider, and a plurality of current mirrors. The timing currents of the VCO are set by the external resistor and are independent of the control voltage Vc of the VCO. The VFO gain is independent of control voltage for improved control of the open loop gain. The timing voltage swing is inversely proportional to the control voltage but is independent of the timing currents. Current mirrors are coupled to the external resistor and the timing current to provide a plurality of timing signals.

Abstract: Method and apparatus for generating a decode window. A phase locked loop locks a pulse edge of a delayed read data (DRD) signal to an edge of a voltage control oscillator (VCO) clock signal. The edges of the decode window are generated directly from the outer edges of the VCO clock signal. This eliminates errors introduced by quarter cell delay lines, particularly in integrated circuit applications. The transition of the VCO clock signal is used to define a nominal center position coinciding with the mean center position of a data stream. Differential control signals are utilized to shift the VCO transition so that it may be synchronized with the mean bit center position and compensate for non-symmetrical peak jitter. The VCO transition may be shifted without changing the period of the VCO clock signal.

Abstract: A low power, astable multivibrator which operates on supply voltages as low as 1.5 volts and is suitable for controlling the application of power to power consuming electrical devices in battery-powered applications is disclosed. A transistor circuit which utilizes relatively large resistance values and positive feedback is presented. Resistance values are sufficiently large to bias transistors so that operation of the transistors in their saturation regions would be prevented without the application of the positive feedback.

Abstract: A voltage controlled oscillator is provided which includes a pair of gain stages constituting a positive feedback path, a pair of buffer stages in cross connection with the gain stages, a pair of loads connected with the corresponding gain stages, each having a parallel connection of an active device resistor and a clamping diode, and a pair of voltage controlled current sources connected with the corresponding gain stages, for supplying constant currents to the gain stages. A timing capacitor is connected with the input sides of both voltage controlled current sources, and is charged or discharged by the constant currents from the current sources.

Abstract: A calibrated-weight balance for converting an electrical analog signal to a binary signal as applicable to flash-type analog-to-digital converters is composed of a bistable multivibrator having two transistors (15, 16) and two resistors (25, 26). In the reference channel (15, 25), a current I.sub.0 flows through a resistor (27) connected between drain and ground. In the measuring channel (16, 26), a transistor (17) is connected between a reference voltage (-V.sub.ref) and the drain of the measuring transistor (16). The input of the balance (V.sub.E) is the gate of the third transistor (17). The outputs (Q, Q) of the balance are the drains of the first and second transistors (15, 16). The resistor (26) for supplying the second transistor (16) constitutes the calibrated weight and permits the flow of a current which is a multiple of the current which flows through the resistor (27) of the reference channel.

Abstract: A precision oscillator circuit with synchronous capability. The circuit receives a predetermined discharging voltage and a predetermined charging voltage for setting a precise discharging and charging rate. A comparator in the oscillator contains three transistors connected to each other at their emitters. A latch circuit is provided on two of the transistors for accelerating the speed with which they turn on. An overshoot correction circuit provides additional charging current when the timing capacitor has dropped below the valley voltage threshold. Synchronizing pulses are generated at the capacitor terminal to allow for a plurality of oscillators to operate synchronously when connected in parallel.

Abstract: An emitter-coupled astable multivibrator capable of reducing a temperature drift of an oscillation frequency to zero is disclosed.

Abstract: An astable multivibrator that has an integrating network coupled from the output of one of the transistors for developing an operating potential. The operating potential is coupled to the RC timing networks that interconnect the two transistors such that when the transistors are switched by a horizontal sync pulse, the duty cycle is compensated.

Abstract: This invention relates to a blocking oscillating converter for transferring energy from a source of power, such as a vehicle battery, to a storage means, such as an energy storage capacitor in a capacitor discharge ignition system. A novel control and feedback circuit incorporated in the blocking oscillator allows the drive level to the switching transistor to be controlled in response to the peak current in said transistor as well as the output voltage of the blocking oscillator. Furthermore the control circuit allows the blocking oscillator to be turned off during the short period of time after each spark discharge that is needed for turnoff of a switching device used to control that discharge.

Abstract: A tunable oscillator circuit provided with a pair of oscillator transistors whose bases are crosscoupled to the opposite collectors, and provided with a capacitance which is arranged between the emitters of the oscillator transistors, each emitter being AC-connected via an emitter current source to a reference voltage is disclosed. In order to considerably increase the tuning range without being limited in the choice of the output amplitude, a pair of buffer transistors in common base configuration is added whose two collectors are connected via a pair of collector resistors to a supply voltage and constitute an output of the tunable oscillator circuit, said pair of buffer transistors arranged in a cascode configuration with the pair of oscillator transistors by being coupled to the collectors of the oscillator transistors.

Abstract: An integrated circuit device includes a timing apparatus arranged to produce timing signals whose frequency is a multiple of that of a clock signal. The timing apparatus, which includes a phase locked loop, is formed on a single chip and no external components are necessary. The phase locked loop includes a convertor and filter circuit (11), the convertor (14) including two transistor current sources (19,24) whose current magnitude is determined by a current reference circuit (13) including current mirror transistors (28, 31). The current sources (19, 24) are controlled by increase and decrease output signals from a phase and frequency comparator (7) such that the output of the convertor (14) depends upon the mark space ratio of the comparator output signals. The output of the convertor (14) is filtered and then fed as a control voltage to a voltage controlled oscillator (12).

Abstract: An input MOS transistor receives an input voltage and produces a current corresponding to the input voltage. A charge/discharge circuit charges a capacitor alternately in two different directions by the output current of the transistor. A select circuit alternately selects and produces one of the potentials at either of the electrodes of the capacitor. A single two-input comparator compares a reference potential with a potential of the output signal of the select circuit. The select circuit produces a signal corresponding to the comparison result. The select circuit allows the output signal of the comparator to be transmitted alternately to the set input terminal and the reset input terminal of a flip-flop. The flip-flop is set and reset by the output signal of the switch means to produce an oscillating signal. According to a change in the level of the oscillating signal, the charge/discharge circuit switches the charging direction of the capacitor.

Abstract: A voltage controlled oscillator includes an oscillator having at least one first capacitor. The oscillator receives first and second input voltages and charges the first capacitor with a first current corresponding to the first input voltage. The oscillator oscillates at a frequency corresponding to the first and second input voltages. To remove the adverse influence on the oscillating frequency by the change of process parameters caused in the stage of manufacturing the voltage controlled oscillators, a second capacitor is charged for a predetermined period by a current corresponding to the first voltage. After the charging of the second capacitor ends, a sample/hold circuit samples and holds the charged voltage across the second capacitor. An operational amplifier receives, at its positive input terminal, the output voltage of the sample/hold circuit, and, at its negative input terminal, the reference voltage.

Abstract: In the horizontal drive of a raster scanned video display, a free running astable multivibrator responsive to a synchronization input signal provides a horizontal output signal to horizontal deflection circuitry for synchronizing the video display's raster scan with the video information presented thereon. The astable multivibrator includes a pair of coupled transistors which are alternately rendered conductive in accordance with the time constant of a respective RC network associated with each transistor. To compensate for the temperature-dependent operation of the transistor pair which causes the multivibrator's operating frequency to increase with increasing temperature, a pair of back-to-back coupled diodes are connected to provide the synchronization input signal to one RC network so as to increase the charge on a capacitor within the network, the time constant of which is similarly increased. The temperature-dependent change in voltage across the diodes compensates for the change in V.sub.

Abstract: Integrated laser diode devices are utilized as repeater elements and logic circuit elements in fiber optic and other light transfer systems. One embodiment discloses a six layer device (10) which is triggered not by an external electrical gating source, but by an external light source (8, 9) as from an optical fiber. Another embodiment operates a laser diode in a bilateral mode. That is, depending on the polarity of the applied voltage bias V to the device (50), two separate light pulses are emitted from different regions (56, 52) of the crystal. A further embodiment utilizes the semiconductor laser as a logical AND function. When the electrical bias (V) of the device (60) is set so that when at least two external light sources (67, 68) are applied, the device will emit laser light (69). Still another embodiment utilizes two semiconductor laser devices (911, 913) as an astable optical multivibrator (90).

Abstract: A resistor, together with a charging capacitor, is connected in series between the emitters of transistors to constitute an emitter-coupled astable multivibrator to be used with a voltage-controlled oscillator. The resistance of the resistor is given by:R.sub.a =(.tau..sub.d1 +.tau..sub.d2)/2C.sub.awhere C.sub.a is capacitance of the capacitor and (.tau..sub.d1 +.tau..sub.d2) is a delay time during one period of oscillation, as determined by the circuit elements.

Abstract: A current mirror circuit capable of accurately setting the ratio between input current and output current. The circuit includes a plurality of input terminals and a plurality of output terminals. A plurality of transistor pairs is provided with the first transistor of each pair having its collector connected to an input terminal. In addition, the collector of each first transistor in each pair is coupled to its own base. The bases of the transistors in each pair are coupled together, while the collector of the second transistor in each pair is coupled to an output terminal. The transistors connected to input terminals have their emitters coupled together and grounded through a first resistor. The transistors coupled to output terminals have their emitters coupled together and are grounded through a second resistor. Such a circuit allows ratios between input and output current to be set very accurately.

Abstract: A programmable oscillator includes first and second transistors having their emitters coupled by a capacitor, and a pair of current sources coupling respective transistors to ground. A switching means is provided having a first state coupling the collector of the first transistor to the base of the second transistor and coupling the collector of the second transistor to the base of the first transistor, and a second state coupling the collectors of the first and second transistors to ground such that when the switching means is in the first state, the first and second transistors switch on and off in alternating fashion, and when the switching means is in the second state the first and second transistors remain on continuously.

Abstract: A PSK modem has a transmitter for converting received digital signals into corresponding PSK output signals and a receiver for receiving PSK signals and converting into corresponding digital signals. The receiver has a dual-integrator voltage controlled oscillator in which, during any given cycle of oscillations, one-half of the circuit is integrating toward the threshold voltage while the other half is idle. When the output of the integrating half reaches the threshold voltage, a control flip-flop toggles and the formerly idle integrator half begins to integrate, allowing the other half to stabilize before the next cycle of oscillation.

Abstract: The invention relates to a quartz oscillator comprising two transistors to whose base terminals the collector voltage of each one of the other transistors is applied, a two-terminal network incorporating a quartz resonator being connected to the emitter of one of the transistors. The collector voltage is applied to the corresponding base via a semiconductor junction. The oscillator further includes respective emitter and collector impedances for the transistors in which the product of the emitter impedances is greater than the product of the collector impedances. When the supply voltage is sufficiently low so that the collector-base diodes of the transistors are always in the non-conducting state, the oscillator frequency is independent, to a very large degree, of saturation phenomena of the two transistors. When manufactured in integrated circuit form, only one additional exterior terminal is required for the connection of a quartz resonator.

Abstract: A circuit is disclosed for driving a piezo ceramic device as used in smoke alarms or other audio warning devices. The circuit detects the resonant frequency of the piezo horn and provides an alternating current at the resonant frequency of the horn for maximum sound output. The circuit has a self starting resonant oscillation characteristic. Two pairs of switches act in concert to alternatingly connect each side of the piezo horn to the supply voltage and ground, causing the maximum voltage swing across the piezo horn to be effectively twice the available power supply voltage.

Abstract: A silicon integrated oscillator circuit is connected with a capacitor and produces a highly precise and stable triangular output voltage. Both the charge current and the discharge current are proportional to one reference current. A switching circuit terminates the charge and discharge intervals when the capacitor voltage reaches a level that is equal to intermediate points on first and second resistive-voltage-divider circuits, respectively. This is accomplished by a differential-transistor-pair comparator having the base of one transistor connected to a high voltage one of the reference points and a third transistor, which is connected collector to emitter across the one transistor, having a base connected to a low voltage one of the reference points.

Abstract: A source of pulses for the electronic suppression of pain is represented by a multivibrator wherein the amplitude of the output signal is double the value of the feeding voltage. The principle of the invention resides in a multivibrator provided with two sets of complementary pairs of transistors, one set of which works simultaneously as a switch and a feeder of voltage doublers. The multivibrator is fed by this increased voltage so that at the output, pulses of double amplitude arise, i.e. an amplitude four times greater than the value of the feeding voltage.

Abstract: An emitter coupled oscillator having a wide bandwidth capability is tuned by an applied voltage or current. The oscillator obtains its feedback coupling by means of a differential amplifier which greatly reduces the second order temperature versus frequency drift. This is accomplished by forcing the oscillator to trip under conditions which greatly reduce V.sub.BE in the switching transistors.

Abstract: Accurate and reliable multivibrators are achieved having most of the advantages of on-chip circuits and producing signals with long cycle periods. An off-chip capacitor (1) in an RC timing circuit is charged during the period defined by on-chip capacitor (31) and resistance (33 and 11) RC timing circuit. The cross-coupled circuit has switches (17) and (19) on at least one side, each effective to connect operating potential to respective ones of the two RC circuits. Each has at least two switches (190) and (270) connected in parallel on the other side of the circuit, each operated by respective ones of the two RC circuits of the first side to hold the other side to ground until both RC circuits have operated for preselected periods. Bootstrap voltage from a capacitor (51) is employed to gate the switch FET (45) to the off-chip capacitor (1) strongly on.

Abstract: A circuit for a flasher unit comprises a flasher relay controlled by an astable multivibrator, the multivibrator having an RC-element with an inverter connected in front thereof, the inverter being controlled in response to the switching condition of the flasher relay.

Abstract: In an oscillator circuit responsive to a predetermined temperature and including an astable multivibrator, a switching transistor inverts an output voltage from a first transistor of the multivibrator with a predetermined time delay, and a feedback capacitor is responsive to the inverted output voltage from the switching transistor to bias a reference capacitor connected between the output terminal of the first transistor and the input terminal of a second transistor of the multivibrator at opposite voltage polarity relative to that of a terminal voltage across the reference capacitor, a capacitance of the feedback capacitor being determined to turn off the second transistor due to the bias of the feedback capacitor when ambient temperature becomes the predetermined one under exposure of the second transistor to the ambient temperature.

Abstract: An oscillator circuit which demonstrates stable operation over a wide range of supply voltages and process variations. A latch circuit is controlled utilizing a timing capacitor. A constant current source is applied alternately to opposite sides of the timing capacitor through a series of switching gates which bootstrap the voltage across the timing capacitor, with the switching gates being controlled by the output of the latch circuit.

Abstract: A low frequency oscillator of the astable type having good frequency stability, fast starting, good immunity to DC loading, and suitable for fabrication in integrated circuit form. First and second switching transistors of the astable multivibrator are cross-coupled by a coupling capacitor and a frequency determining crystal. Base drive to the respective switching transistors and charging current to the capacitor and crystal are provided by a pair of differential amplifiers which are referenced to a forward biased diode. The differential amplifiers are also connected to respective collector terminals of the switching transistors. The capacitor is of small value suitable for containment within an integrated circuit with the oscillator circuit. The differential amplifiers substantially increase the impedance levels in the oscillator and shift base drive to the switching transistors to minimize the effects of DC loading at the output terminals of the oscillator.

Abstract: In the disclosed device, a square wave generator drives a network composed of a parallel resonant circuit in series with a series resonant circuit. The resonant frequency of the parallel resonant circuit is substantially equal to the fundamental frequency of the square wave voltage generator and lower than the resonant frequency of the series resonant circuit. The resonant frequency of the series resonant circuit is lower than the frequency of the third harmonic of the square wave voltage generator. A load coupleable to the parallel resonant circuit has a complex impedance which shifts the current at the fundamental frequency about 30.degree. relative to the fundamental square wave voltage.

Abstract: First and second NPN transistors are direct connected in an astable multivibrator configuration. Each collector is connected to the positive terminal of a DC power source through series connected diodes. A resistor, which is selected to control the amplitude of oscillation, is connected between the collectors. The frequency of oscillation is controlled by a frequency determining component which is connected between the emitters of said transistors. The emitters are connected to current sources.

Abstract: A method and apparatus for producing near constant duty cycle over a wide range operating voltage by connecting clamping transistors across critical timing capacitors so as to eliminate undesirable charge injection in MOS and CMOS oscillator systems. In an oscillator in which two inverters are cross-coupled through timing capacitors, each timing capacitor is shunted by a clamping transistor controlled by the output from one of the inverters. The oscillator may be used in a hand-held calculator.

Abstract: Disclosed is an integrated circuit voltage controlled astable multivibrator with external fixed components: resistor RT and capacitor CT. The multivibrator has a center frequency which is a function of: the value of capacitor CT, the amplitude of a constant current Il used to charge and discharge capacitor CT, and a voltage VT. The period timed is proportional to VT/Il where VT is half the voltage swing across capacitor CT. Undesired frequency variations are minimized by generating both current Il and voltage VT in similar matched networks and from the same voltage source so that Il and VT track each other.

Abstract: A fail-safe AND logic circuit including a free-running multivibrator and a pair of voltage reference networks. The multivibrator includes a pair of common emitter transistor amplifiers. The transistor amplifiers are separately biased and powered by an individual one of a pair of voltage reference networks so that a.c. oscillations are produced by the multivibrator when a separate negative-going pulse coincidentally appears on both of the pairs of voltage reference networks.

Abstract: A fire alarm having in a single unit a battery and a fire detecting section energized by the battery to detect abnormal environmental conditions such as heat and smoke to provide an output signal. A voltage decrement detecting section detects a voltage decrement of the battery to provide an output signal. A warning unit such as a buzzer is coupled to a switching circuit for operating the warning unit upon reception of the output signal from either the fire detecting section or the voltage decrement detecting section through an input terminal thereof. To reduce power consumption, the system uses a multivibrator having C-MOS IC, inverters.

Abstract: A DC-to-DC converter employs four transistor switches in a bridge to chop DC power from a source, and a voltage multiplying diode rectifying ladder network to rectify and filter the chopped DC power for delivery to a load. The bridge switches are cross-coupled in order for diagonally opposite pairs to turn on and off together using RC networks for the cross-coupling to achieve the mode of operation of a free running multivibrator, and the diode rectifying ladder is configured to operate in a push-pull mode driven from opposite sides of the multivibrator outputs of the bridge switches. The four transistor switches provide a squarewave output voltage which has a peak-to-peak amplitude that is twice the input DC voltage, and is thus useful as a DC-to-AC inverter.

Abstract: In this relaxation oscillator first and second electrically controlled constant current generators are used to provide proportionately related first and second currents to first and second terminals, respectively, between which the timing capacitor is connected. Set-reset, or R-S, flip-flop means is set and reset by the voltage at the first and second terminals, respectively, departing in a first sense from the voltage at a reference voltage bus by a predetermined amount. First switching means responds to the R-S flip-flop reset condition to complete a connection of the first terminal to the reference voltage bus and responds to the R-S flip-flop set condition to interrupt that connection. Second switching means responds to the R-S flip-flop set condition to complete a connection of the second terminal to the reference voltage bus and responds to the R-S flip-flop reset condition to interrupt that connection.

Abstract: A multivibrator circuit having a pair of capacitor cross-coupled transistors arranged to form a flip-flop circuit. The base and collector currents for the flipflop transistors are concurrently varied by respective current sources controlled by a multivibrator input signal. The circuit has a constant Beta requirement for the transistors over a wide frequency range while maintaining a high speed operation.

Abstract: A self-oscillating, push-pull inverter circuit is described wherein positive feedback signals are provided alternately to the bases of a pair of switching transistors by a single miniature saturable current transformer. The circuit performance relies on a pair of diodes having special characteristics connected across the base-emitter junctions of the respective switching transistors.

Abstract: The converter device transforms a changing direct signal generated by a source of direct current, into a signal whose amplitude is substantially greater than that of said changing signal, at least for certain values of this signal. It comprises a first transistor, an inductance with a high overvoltage coefficient wound on a core of ferrite and arranged in the collector circuit of said first transistor, so that one terminal of this inductance is directly connected to the collector of said transistor, a second transistor of which the collector is directly connected to the base of the first transistor, a connecting capacitor between the collector of the first transistor and the base of the second transistor, and a polarizing resistance arranged between the base of the second transistor and one terminal of said source.

Abstract: A voltage controlled oscillator (VCO) to produce a variable frequency and duty cycle output proportional to the applied (input) voltage. The VCO comprises RC charge networks to vary both the frequency and duty cycle of an astable multivibrator with applied voltage variations. The VCO has particular application for low voltage and low frequency operation.

Abstract: A circuit for quickly discharging a timing capacitor which is connected between the collector of a first transistor and the base of a second transistor, and which is charged via a current source connected to the collector of the first transistor. The circuit includes a third transistor whose conduction path is connected across the capacitor and whose control electrode is connected to the emitter of the first transistor. A turn-on current supplied to the base of the first transistor causes the timing capacitor to be discharged by a current whose amplitude is approximately equal to the turn-on current multiplied by the product of the forward current gains of the first and third transistors.

Abstract: Oscillators that include charge-flow transistor logic elements, each logic element including a charge-flow transistor and a load element, in combination. The charge-flow transistors have TURN-ON times t.sub.on and TURN-OFF times t.sub.off that can be very different from one another (e.g., t.sub.on can range from milliseconds to hundreds of seconds; whereas in the charge-flow transistors shown herein t.sub.off is typically less than one microsecond). The magnitude of t.sub.on is sensitive to the environment; hence, the period of oscillation can be used as a measure of an environmental condition.

Abstract: An astable multivibrator includes a first transistor a single capacitor arranged in a time constant circuit, coupled to the emitter of the transistor and a potential divider circuit coupled to the base of the transistor to apply a selectable portion of a bias supply thereto. A circuit including another transistor of polarity opposite to that of the first transistor responds to the first transistor in its conductive or non-conductive state for determining the portion of potential applied to the first transistor such as to drive the transistor into greater conduction when it is conducting and further from conduction when it is non-conducting. The threshold levels of the transistors track the voltage supply, which may be varied, such that the frequency and duty factor of the multivibrator are invariant with changes in voltage supply value.

Abstract: A multivibrator in which a timing capacitor is connected between the collector of a first transistor and the base of a second transistor and in which a current source connected to the collector of the first transistor provides the charging current for the timing capacitor. The conduction path of a third transistor is connected between the collector and base of the first transistor and its control electrode is connected to a control voltage point for controlling the charging period of the capacitor and for ensuring oscillation when the multivibrator is connected as an astable multivibrator.

Abstract: Improvements in battery operated smoke detector electronics including micro power astable multi-vibrator circuitry which has fast reliable switching of the inverters and electronic circuitry for single or dual ionization chamber smoke detector which maintains constant smoke detector sensitivity throughout the usable life of the battery.

Abstract: A lighting system for bicycles and the like which incorporates forwardly and rearwardly mounted lighting assemblies. Each of these assemblies includes right and left turn indicator lamps mounted within housings each having an outwardly directed lenticulated lens, the discrete facets of which protrude in a direction outwardly from an associated lamp. These lenses are utilized in conjunction with lower energy level inputs to the lamps in which an oscillatory circuit to optimize the consumption of energy from a bicycle mounted battery power supply. The batteries of this supply as well as impedance and oscillatory logic circuitry in addition to a recharging circuit are mounted in a unitary housing which is readily removable from the frame of the bicycle for purposes of leaving it unattended. Through the use of a harness incorporating a releasable electrical coupling, this more elaborate and expensive component of the bicycle may be retained for safe keeping when the bicycle is stored or parked.

Abstract: A temperature sensitive thyristor is incorporated with an astable multivibrator to provide active temperature sensing. Below the switching temperature Tsw of the thyristor, an oscillatory signal is present at the output of the multivibrator. When the temperature exceeds Tsw, oscillation ceases because of the shunt path provided through the thyristor when it intrinsically switches to its low resistance on state above Tsw. Cooling results in resumption of oscillation. This is a "fail-safe" arrangement because component failure also provides a warning condition (absence of oscillation).

Abstract: A computer controlled facility is provided to detect capacitance, and hence defective connections, between a group of wires in a telephone handset cord and terminal blades of plugs connected at both ends of the cord. The test depends upon ascertaining the capacitance between a properly connected terminal blade and wire and the other terminal blade and wire connections to provide exact indications of the terminal blades and wires which are not properly connected. Capacitance is detected by connecting a good wire and blade connection along with another wire and blade in a capacitance network associated with one stage of a free running multivibrator which produces an output wave in accordance with the capacitance between the connected pairs of wires and blades. A delayed pulse is cyclically generated to act in conjunction with the output wave to control a bank of indicator lights to provide an indication of any defective wire to blade connections.