This variable frequency circuit was found in a Popular Electronics from the 90s. The circuit outputs to a small speaker and can be powered by voltages as low as 3 V.
In this circuit, which uses one of the four comparators of an LM339 (or LM139 or 239), capacitor C1 and...
This timer activates a relay after a time interval of up to 15 minutes has elapsed, starting from...
This inverter can reach a power of 300 W depending on the transformer used. In this case, a...