LED Soft-Touch Fill Circuit

A 6-LED analog circuit that lights up progressively while a push button is held, and fades out gradually when released — no microcontroller involved.

The effect is created by a diode ladder network: each LED needs to overcome one more diode drop than the last, so they turn on in sequence as the control voltage rises. Two transistors (BC547, BC557) handle the switching, while a capacitor and resistor network sets the charge/discharge timing that drives the fade-in and fade-out.

Designed on paper, tested and debugged on a breadboard, then soldered onto perfboard for the final build.