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 alarm circuit was found in the July 1992 Radio Electronics magazine. The circuit uses a small...
Found in a Philips publication from the 1970s, this circuit uses a DO040, which is difficult to obtain...
This simple nicad battery charger uses a current regulator with the LM350. This integrated circuit must be...