Telephone-triggered light controller

How it works

A ring detector triggers a timer, and a line-state comparator keeps the light command active while the handset is lifted. When the call ends, the timing capacitor charges until the timer returns to its idle state.

The archived design holds the light on for approximately eleven seconds after the last ring or after the handset is replaced. An optoisolator couples the control signal to the switching stage.

On the bench

This combines telephone-line and potentially mains hazards. Use isolated simulators and a low-voltage indicator for study; the original drawing needs a full isolation and enclosure review before practical installation.

Resources & provenance

Rewritten from the original circuits/tel/nu4p01x_tel002.php page. Component values and historical performance claims have not been independently bench-tested. The circuit figures have had their watermarks removed.