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 inverter bistable buffer circuit was obtained in a Hands On of the 90's. Next to the circuit we...
We find this circuit in a Popular Electronics of the 80's. The frequency range depends on C1 and...
Suggested by a Popular Electronics from the 90s, this circuit triggers an external load, relay or...