Tester Circuits


Simple Cat.5 Network Tester

This circuit came from a need for a “quick and dirty” network tester that could be operated by one person. All the commercial units I tried required a person at the other end to check the remote LEDs, as the transmitters could not be made to cycle through the test continuously to allow one person […]


4-20mA Current Loop Tester

This design will interest technicians who work on pneumatically operated valves and other 4-20mA current loop controlled devices. Although 4-20mA signal injector/calibrators are available, this one is both cheap to build and easy to operate. When first powered up, the circuit sinks 4mA of current. If switch S1 is pressed, the current level slowly ramps […]


Simple Function Generator

Simple triangle-wave generators have a weakness in that the waveform of their output signal normally cannot be modified. The circuit presented here makes it possible to smoothly alter the waveform of a linearly rising and steeply trailing saw-tooth signal through a symmetrical triangle-wave to a slowly trailing, steeply rising linear sawtooth. The wanted waveform may […]


Thyristor Tester

The circuit in the diagram is a very handy tool for rapidly checking all kinds of thyristor (SCR, triac, …). In case of a triac, all four quadrants are tested, which is done with S3, while in case of a standard thyristor, a positive power supply and trigger current need to be set, which is […]


Wire Continuity Tester by LM709

Wire Continuity Tester : While detecting discontinuities on a circuit board, it is probable to include resistors, semiconductors or other elements in measurements. This situation may cause wrong results. On the other hand sometimes the voltage or current of the multimeter may defect some circuit components. Our circuit overcomes this inconvenient conditions. The circuit determines […]


Panner Waveform Generator

This device is a microprocessor controlled waveform generator that can be used for driving a voltage controlled stereo panner for music applications. Panning is simply the movement of a mono audio signal between the left and right channels of a stereo sound system.The circuit can also be used to drive other voltage controlled modules that […]


Mains Frequency Monitor

Here is a simple frequency counter designed to monitor the 240VAC mains supply. It as a frequency range of 0-999Hz, so it could also be used with 400Hz equipment. Standard TTL/CMOS logic is employed for the counters and display drivers, while an ELM446 (IC1) generates accurate 1Hz pulses for gating. This device utilizes a 3.579545MHz […]


Water Level Indicator Using 7-Segment Display

This water-level indicator uses a 7-segment display, instead of LEDs, to indicate the water level (low, half and full) in the tank. Moreover, a buzzer is used to alert you of water overflowing from the tank. The circuit shows the water level by displaying L, H and F for low, half and full, respectively. The […]


DC or AC Voltage Indicator

Detects 1.8 to 230 Volts DC or AC, Minimum parts counting This circuit is not a novelty, but it proved so useful, simple and cheap that it is worth building. When the positive (Red) probe is connected to a DC positive voltage and the Black probe to the negative, the Red LED will illuminate. Reversing […]


Relay Switch Activated by Tone and Signal

The essence of the circuit is for the input of tone and signal to provide an activation for the relay switch. Relay – an electrically operated switch where the current flowing through the coil of the relay is creating a magnetic field which attracts a lever and changes the switch contacts, thereby making its state […]