Crystal Tester Circuit Schematic Diagram

A crystal tester circuit is very simple, it contains only oscillator and detector inside. This crystal tester circuit uses one transistor for the oscillator and one transistor for the detector. Here is the schematic diagram of the circuit:


crystal tester circuit diagram

The mechanism of this crystal tester is very simple. If a good crystal is connected to the test lead, the oscillator will work, and an AC signal will be generated at Q1 emitter. This AC signal will flow through capacitor C3 and trigger the Q2 to light the LED indicator. The diode 1N4148 provide the back path for the AC signal.  If the crystal is bad, the oscillator won’t work, and there is only DC voltage level at Q1 emitter. This DC voltage level won’t trigger the Q2 transistor since the capacitor C3 block any DC signal.  You can use any high gain high frequency transistor for this crystal tester circuit, in case you can’t find exact transistor series as shown in the schematic diagram.

One thought on “Crystal Tester Circuit Schematic Diagram

  1. Henry Bowman

    The crystal tester will not test crystals below 1MHZ.
    It also does not provide sufficient amplification, for some crystals, thus providing a false indication that they are bad. It is a great design however, and just needs a selector switch to provide different tank capacitance and another stage of amplification before Q2.

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