Simple Crystal tester – The idea for this crystal tester circuit sprung out of the need of testing a large number of oscillator crystals lying unused in a big hobby box. testing the crystals one by one without the appropriate device would have been very slow and a time consuming task. Commercial crystal testers are however very expensive, that is why this simple electronic crystal tester was born. The electronic circuit can be used to test crystals with frequencies from 100kHz up to 30MHz. The current consumption is low: around 10 to 14 mA.