Crystal Tester

crystal tester XTal Tester

Crystal Tester

We have crystals lying about, but don’t know whether these are still working all right. The crystal tester described here will quickly show whether a crystal can be used or should be discarded.

crystal tester XTal Tester circuit

R1 27kΩ
R2 1kΩ
R3 560Ω
C1 1n (102)
C2 100pF
C3 1n (102)
C4 4.7n (472)
D1 1N4148
D2 1N4148
Q1 BC550C
Q2 BC550C
X Crystal
Sw1 Switch
BT1 9V Battery

Transistor Q1 and the crystal under test from an oscillator. Capacitors C1 and C2 form a voltage divider in the oscillator circuit. If the crystal is in good order, the oscillator will work. Its output voltage is then rectified and smoothed by D1 and C4 respectively. The resulting direct voltage at the base of Q2 is sufficient to switch this transistor  on, so that the LED lights.

The circuit is suitable for use with crystals of a frequency between 100kHz and 30MHz. Current consumption is about 50mA.

Please send your ideas, those are very important for our success…

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