ELECTRONICS

You can use this versatile probe for continuity testing and identification of transistor type and transformer windings. The n-side or p-side of a transistor can be identified quickly in one go. You can make two contacts with the probe in one hand while the other hand is free. Fig. 1 shows the circuit of the probe. The operation of the circuit is simple. It is driven by an alternating current flowing through two LEDs (LED1 and LED2). So one LED corresponds to forward direction of current flow, while the other shows reverse direction of current flow. This helps to detect orientation of the p-n junction with respect to the probes. The LEDs can be arranged near the probes to glow either for the p-side or the n-side as per your choice. The frequency is determined
by capacitor C1 and preset VR1 connected between gates G1