Suggested by a Popular Electronics from the 90s, this circuit triggers an external load, relay or recorder, when the telephone line receives a call, thus enabling its recording.
This circuit is intended to match impedances for observing signals on an oscilloscope. The FET...
The battery is charged by the photocell that keeps the low consumption beacon in the dark. The...
This is the configuration suggested by National Semiconductor for cascading the LM12. The LM12...