crystal tester

Many electronics hobbyists 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. Transistor T1and the crystal under test form an oscillator. Capacitors C1 and C2form 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 D1and C4respectively. The resulting direct voltage at the base of T2 is sufficient to switch this transistor on, so that the LED lights. 9V 7-38 crystal tester 02 OC) The circuit is suitable for use with crystals of a frequency between 100 kHz and 30 MHz. Current con- sumption is about 50 mA.