This 300 Hz to 3.4 kHz filter was found in the May 1989 Radio Electronics magazine. The circuit requires a symmetrical power supply.
In the circuit shown in the figure we have the way to excite a small speaker from a TTL output. The...
This simple circuit is from a Radio Electronics from August 1952. The current depends on the...
Found in an Electronic Design, this small power source uses a battery as a voltage reference,...