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 circuit is suggested by the National Semiconductor Linar Applications Handbook, controlling a DC motor...
This transmitter for modulated infrared remote control was found in documentation from the 90s....
This circuit was found in a 1966 American publication. The critical component is the tunnel diode. ...