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.
The circuit in the figure is a current regulator with adjustment in the range of 0 to 3 amps. The...
This filter with the operational 741 passes the frequency range between 300 Hz and 3,400 Hz. This...
Taken from an Electronics Now from the 90s, this circuit generates signals whose frequency depends on...