SCR Tester (MIN097E)

In many of the assemblies described on this site and in other publications, we make use of SCRs of the 106 series (TIC106, MCR106, C106, etc.).

Knowing if one of these SCRs is in good condition is something that can bring some kind of concern if the reader does not have the appropriate instrument.

For knowing if one of these components is in good condition, we describe a simple tester whose diagram is shown in Figure 1.





The circuit uses two 6 V bulbs as indicators and is simple to use: simply connect the SCR to the circuit and observe the bulbs.

If you do this, the L1 lamp comes on at maximum brightness and L2 is off then the SCR is shorted.

If both lamps remain lit and when S1 is pressed, nothing happens, the SCR is open.

For a good SCR, when pressing S1 the L2 lamp goes off and L1 on.

The assembly of this tester on a wire and clamp terminal bridge to connect the SCR is shown in Figure 2.





We note that other higher power SCRs, such as those in the TIC series for 6 or more amps, cannot be tested by this circuit because they need a higher triggering current than that supplied, when S1 is pressed.




D1 - 1N4002 - silicon diode

SCR - SCR in test - TIC106 or equivalent with any suffix - see text

L1, L2 - 6 V x 50 to 100 mA bulbs

T1 - Transformer with a primary according to the local power grid and secondary of 6 V x 200 to 500 mA

S1 - Pressure switch

R1 - 1 k ohms x 1/8 W - resistor - brown, black, red


Power cord, assembly base, terminal bridge, wires with claws, welder, etc.




Lies Detector (MIN095E)

This ultra-simple circuit detects imperceptible variations in skin resistance. With attention during an interrogation we can check if someone is lying or telling the truth.

Polygraphs, or lie detectors, work based on the small variations in skin resistance, indicated by an instrument, that occur when a person lies. Our circuit is very simple and sensitive, using a VU meter of 200 µA as a detector.

Stroboscopic Lamp Using LEDs (MIN074E)

The circuit in Figure 1 uses LEDs rather than 4 lamps and is powered from a DC power supply or cells. The circuit uses a IC-555 (timer) configured as an astable multivibrator driving a power transistor.

The frequency is controlled by P1 in a range determined by C1, and the pulse duration is determined by R2. These components can be changed from 4.7 to 47 k. White bright LEDs are recommended, but depending on the application, you can use common LEDs of any color.

Fluorescent Stroboscopic Light (MIN075E)

Fluorescent lamps are faster than incandescent lamps, so they are better for producing fast flashes in a stroboscopic circuit.

The circuit shown in Figure 1 is not powerful, but it can be used in some experiments involving bionics such as animal conditioning, working with stress, and others (*).

Digital Voltmeter (MIN070E)

You can use this circuit to have a voltage visual indication in experiments involving different kind of sensors.

Four LEDs form a "bargraph" scale indicating the amount of voltage at the input of the circuit in a range between 0 and 6 volt.

Bio-voltages, voltages produced by experimental or alternative cells, experimental photo-cells and fuel cells can be indicated by this voltmeter.

Circuit Bench