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 was found in a National Semiconductor manual from the 1980s. The integrated circuits used...
This circuit uses a resonant reed relay to recognize the frequency of an input signal. Adaptations...
From the time when photographs developed on paper could be enlarged, this circuit was found in a...