I needed a night light in a dark stairway, but there was no outlet. A motion detector was out of the question due to pets, and the stairway light couldn’t be converted to a night light because it shares a circuit with other important lights.
That left me with one option: make a night light that sits as a ring underneath the ceiling-mounted smoke detector.
I used a pair of these LED night lights that I found at the hardware store. They have a light sensor to save an LED’s worth of power.
The housing can be pried off with a flathead screwdriver.
This is what the circuit board looks like. It’s compact, but not compact enough.
It’s necessary to flatten the circuit by bending the transistor flat, and soldering extension leads on the 2 capacitors to allow them to lie completely flat. The 120V inputs are replaced with a wire and the output LED is given a longer extension.
The plan is to keep the LED away from the photodiode.
The body of the night light ring is made of ShapeLock (Instamorph). I built a simple jig with dowel pins to mark the holes, and arranged the electronics around that.
Then I used the smoke detector’s mounting plate to press the plastic flat.
Waxed paper prevents the moldable plastic from sticking to either the wood or the mounting plate. This is the last good chance to adjust the photodiodes and LEDs to make sure they sit well on the perimeter of the ring.
After a few minutes in the freezer, the finished prototype is removed from the jig.
Fortunately the mounting bolts for the smoke alarm were long enough to accommodate the extra distance. Without the diffusers, the light seems a little bright. But this is an excellent result.