This circuit is one of many that the reader can find in this section for testing crystals. The circuit uses an indicator LED. Transistor Q1 determines the maximum crystal frequency that can be tested.
This '80s circuit drives an infrared LED, producing a modulated signal. Modern higher power LEDs...
We found this circuit in the February 1987 issue of Radio Electronics magazine. It is based on an...
This simple 1 transistor circuit was found in an American documentation from the 60's. The...