Originally this circuit was created to produce synchronism pulses in TV cameras SSTV (Low scan frequency), however it can be adapted for other purposes. The integrated circuits are common TTL.
The figure shows three circuits for using headphones in amplifiers with speakers that do not have...
In this charger, the charging current is basically limited by the LEDs. The transformer is a low...
This configuration is from an old integrated circuit manual. The circuit can be applied to modern...