A corner cabinet of just installed kitchen cabinets was a little dark and I had left-over under cabinet LED strip lighting so this project was hatched!
The lights turn on when a magnet on the door moves away from a magnetic reed switch in the cabinet. This circuit should last for a very long time with intermittent use.
- Battery holder for 2 C size batteries
- SPDT reed switch (eBay)
- Supermagnet with countersink hole (eBay)
- LED strip lighting (eBay)
- 3V to 12V DC-DC boost converter circuit board (eBay)
- Wire and solder
- Small enclosure
- Mounting screws
Step 1: Magnetic Sensor
I didn't like the large size of any pre-made magnetic reed switches so I made one.
Reed switches are glass vials with electrical contacts inside that are operated by an external magnetic field. Most reed switches close when a magnet is brought near but I wanted the opposite - so when a super magnet attached to the cabinet door moves away, the switch closes and the battery energizes the rest of the circuit. A single-pole double-throw reed switch worked perfectly for this.
I bought a miniature SPDT reed switches and put it in a copper tube with a tab soldered onto it. See my Building with Brass Instructable on brass fabrication. The tube protects the glass vial and brass does not interfere magnetically. Solder wires to the switch contacts that pass current when a magnet is withdrawn. Insulate the solder joints with tape or shrink tubing.
I spray painted the switch to match the cabinets.
Step 2: Wire Circuit
Solder up the circuit according to the diagram above. Test it with the magnet before installation.
Be sure not to exceed 1 amp with this DC voltage step-up module. That will be determined by the number of LEDs in the chain.You can test the current draw with a multimeter before final soldering. A very long string of lights is probably not appropriate with this sort of battery powered circuit.
Alkaline C cells can produce 8 amp-hours of energy. The 2 foot LED string I used takes only 400mA so they should last 20 hours!
Step 3: Install and Enjoy
Screw all of the components inside the cabinet. The LED strips have self- adhesive on the back. I added a couple sticky wire holders to tidy up the wiring so it wouldn't get caught.