This circuit for audio signals was found in the March 1990 Radio Electronics magazine. The circuit uses a unusual optocoupler that can be replaced with an equivalent one.
When the input voltage is higher than 2/3 of the power supply voltage the green LEDs glows. When...
This is a conventional alarm that uses NO and NC type sensors for doors and windows. The circuit is...
This circuit was obtained in a 1972 RCA power transistors manual. The transistor admits...