Versatile Digital Teste

It is difficult to detect the fault and troubleshooting digital circuits. Here is a simple and versatile circuit of digital tester for detection of condition of the components and also indicates the nature of defect.

Circuit description of versatile digital tester

This whole circuit of versatile digital tester is designed and fabricated around CMOS hex inverter buffer CD4049 containing six independent inverters (a – f). Where inverter (a) form basic integrator. Inverter B and C form the Schmitt trigger. Preset VR1 & VR2 is used to controls the frequency of the square wave oscillator and adjust the duty cycle to 50% respectively. The output of each inverter is fed to another inverter. Inverters d with e produce complementary output. A.C. output is obtained from complementary pair (inverter d and e) used to drive two LEDs (LED1 and LED2) where resistor R6 is used as current limiter of LEDs.

Inverter f is designed to detect logic state where LED3 and LED4 indicate high and low logic state respectively and is depends upon logic condition at probe P5 with respect to probe P6. Transitional point (where the LEDs just switch off) is adjusted by preset VR3.

Generated frequency from versatile digital tester is taken from probe P1 and P2 and is set by preset VR1 where frequency range of 10 Hz to 1 KHz in LF position and 1 KHz-70 KHz in HF position. The LF and HF position is decided by switch SW1­.

Probe P3 and P4 is used to test semiconductor and its direction (forward bias and reverse bias). The forward bias of semiconductor is decided with LEDs direction. Either glowing LED indicates functional order and polarity. Resistive component can also be tested through probe P3 and P4, glowing both LEDs indicate component is functioning.

Probe P5 and P6 is used to test logic state where probe P6 is connected to ground of the circuit under test. Supply voltage must be 6V.

digital all in one tester


Resistors (all ¼-watt, ± 5% Carbon)

R1,R5, = 10 KΩ

R2 = 8.2 KΩ

R3 = 18 KΩ

R4 = 330 Ω

R6, R7 = 560 Ω

R8 = 680 Ω

VR1 = 2.2 MΩ

VR2 = 2.2 KΩ

VR3 = 220 KΩ


C1 = 0.033 µF

C2 = 390 pF

C3 = 3.3 pF


IC1 = CD4049B


SW1 = Single pole double throw (SPDT) switch

SW2 = Push to ON/OFF switch

LED1 – LED4 = Different Color LEDs



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