Automatically turning on/off closet light when the door opens/closes

This isn’t a Glowforge project so much as it was a project where I used my glowforge (and a 3d printer) to create components.

My hallway closet is dark and kind of hard to see into. I wanted to add light, but there’s no power in the closet and I don’t feel nearly qualified enough to run my own power through my house. I also didn’t want to have to flip a switch on and off for the closet light.

After a few months of noodling on the design, I finally built it this weekend:

  • 5m USB-powered white LED strip, lining the back of the door frame
  • Powered by 10,000ma USB battery pack mounted to wall in a 3d printed casing.
  • 3d printed “door arm” with a magnet embedded in the top mounted to the top corner of the door.
  • Normally closed reed switch (sort of, I’ll get back to this later) mounted in a lasercut casing, mounted to the top of the door frame.

Now, when the door is closed, the lights are off. The moment the door is opened, the lights come on!

I originally was thinking about a motion or PIR sensor, but that was going to draw power constantly. I did NOT want to have to recharge the battery every week or two. That’s when I came up with the idea for using a reed switch - it shouldn’t draw any power unless the lights are on. Since it’s a closet light that won’t be on very often or for very long, the battery should last months.

I needed a normally closed reed switch, but all the closed ones I found on digikey maxed out at 700ma. The battery outputs 2.4A… so I was pretty sure that wasn’t going to work. I found a normally open switch that operates at up to 3A, and I discovered you could flip the reed switch from normally open to normally closed (or vice versa) by permanently adding a second magnet. Which makes sense!

So I used my Glowforge to lasercut a small wooden enclosure for a magnet, then a small enclosure for the reed switch, and dumped a gallon of hot glue into it then mounted to my door frame.

Like I said at the beginning, it had been a long time since my high school electronics class. So long, in fact, that I forgot about the value in using consistent and standard colors for my wires… So I present to you, a red wire that turns into a white wire that turns into a black wire. Because I’m an idiot.

But other than that mixup, I’m very happy with the result. It works great and looks better than I imagined.

The two big things I’m watching for right now:

  • The battery pack overheating (since it fits pretty snug in the 3d printed casing). After a straight hour of being on, it was still room temperature, so I don’t think this will be an issue.
  • How long the battery pack lasts. The LEDs draw so little power, and will be on so infrequently, I think my biggest enemy is going to be the battery naturally losing charge over time. My estimate, based on the manufacturer (Anker), is this should last between 3-6 months. I’m okay charging this system 2-4 times a year.

Any questions?


Yeah why not just upload the pic here? :wink:

But seriously why a reed switch when a plain old mechanical switch would do?

Couldn’t figure out how :joy:. Went back and figured it out though.

The only mechanical switches I could find were door jamb switches, which would have required me to drill out a pretty significant chunk of the door frame. That was a no-go from the missus.


Nothing wrong with magnetic switches for battery powered projects. I’ve used them many times for similar projects.

I built a similar setup for my last GF’s pantry, 12V LED strip around the inside of the door frame lit it up like daylight. 8 D-Cells lasted two years. Nice thing about the magnetic switch was it turned off even if the door wasn’t full closed.

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Yes! I’m hoping my USB rechargable battery lasts > 6 months, since there’s no power draw when the lights are off.

When it starts to dim even slightly, or even one afternoon when you just happen to think of it, just recharge it.

It will last forever that way.

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