Dimmable Light Beam
A PWM-dimmed LED beam on a custom PCB, switched by motion — the first board of mine that went straight from sketch to etch.
- Single TIP122 NPN Darlington handling the LED current, gated by PWM
- Purpose-made PCB replacing the breadboard prototype
- Motion-triggered, with the brightness level set by scene rather than fixed
The smallest project on this site and the one I still use most. A 12 V LED beam, dimmed by PWM through a TIP122 NPN Darlington, on a board made specifically for it rather than the usual perfboard.
A Darlington is not the efficient choice here — the two junction drops cost more headroom than a MOSFET would — but it is forgiving of the gate drive and it was in the parts drawer. For a fixture that draws what this one does, the simplicity won.
The version in daily use is motion-triggered, with the brightness set by whichever scene is active rather than being a fixed level, so the same fixture works as a night light and as a task light. It is also the light driven at 100% by the Scene Select controller’s work and daytime modes.