Using the CA3140 integrated circuit, this switch was found in the June 1986 Radio Electronics magazine. Sensitivity adjustment is made at the trimpot in series with the sensor.
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...