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 figure shows how to implement an OR function with two inputs, using a relay. The relay...
The integrated circuit used in this 1987 project is not very common these days. However, if found...
Found in American documentation from the 1980s, this circuit has a diode feedback. At the exit we...