Universal Test Probe

Posted on Nov 18, 2012

The compact test probe provides rapid `measurement` of voltage levels at digital gates, fuses, diodes, batteries, and

Universal Test Probe
Click here to download the full size of the above Circuit.

others. It does not provide absolute values, but rather it provides a good indication of correct operation or otherwise. Measurements are carried out with pins A and B. If the potential difference between A (the reference pin) and is 1.9 to 2.0 V, D2 will light. If the voltage at is < 1.4 V higher than that at A, D3 will light. Finally, if the potential at is > 11 V, with respect to that at A, Dl will light. Transistor T5 is used as a zener diode. The probe allows the measurement of alternating voltage. The maximum input voltage is highly dependent on the dissipation allowed in Rl. For example, when this resistor is a 0.5-W type, the input voltage can be as high as 200 Vrms. The current drawn by the circuit depends on the number of lighting LEDs: it is not more than 10 mA at a supply voltage of 3 V. In quiescent operation, the current is so low (about 5 ) that an on/off switch is not necessary.

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