This circuit uses an optical coupler to indicate a phone call through a lamp. The circuit is from a Hands-On Electronics from the 90s. The lamp must be incandescent.
We found this circuit in a 1982 documentation, but the circuit can still be easily assembled, as the...
July 2017 - Texas Instruments' new 3 A bq25601 single cell battery charger can be found on Mouser...
When the sensor X1 is opened, the relay is energized. When waiting, the current drained is very...