Saturday, January 10, 2015

Motion-controlled non-intrusive bed light

Don't you hate it when your significant other wakes up in the middle of the night and turns on the bedroom light?
If she also happens to stumble upon some furniture pieces in the process it makes it even more fun.

Just kidding, engineers don't have girlfriends.


Problem 2 was solved by having a remote control for the light, on the nightstand.

Every person should come with a remote

This turns on a lamp behind the bed. The lamp was turned over so it only produces a diffuse light:

Looks nice, when it's not raining
For the first issue (not seeing where stuff is) I reused some LED strip I had lying around, taped it under the bed and added two motion sensors.


The motion sensors turn the lights on when one someone steps near the bed (or gets out of it) and the lights stay on for about 20 seconds.






LED strip going around the underside and one of the motion sensors

Total cost of the project should be less than 25 USD/EUR:
- LED strip - 5-15$.
- power supply - 1-5$, unless you already have one 7,5-12V supply around
- motion sensors - 1-2$ each
- Darlington power transistor - <1$
- cables, tape, time




The motion sensors have 3 pins: VCC, OUT, GND.
You have to stick 3-25V on the VCC pin and you get 3-5V on the output pin, at less than 15mA.


I had a ton of TIP141 lying around so I tested using one of these and it actually worked.

Connections:

  • + 7.5V -> LED strip (+) -> TIP141 pin 2 -> 0V
  • +7.5V -> sensor VCC
  • 0V -> sensor GND
  • 0V -> LED strip (-)



Testing with a 12V automotive bulb for heating issues. At 1A the transistor barely gets warm.


I am using a multicolor strip and want to get a nice reddish color. The red LEDs turn on first, followed by green, followed by blue. By controlling the output voltage you can control intensity and color at the same time:

  • 5V - dim red
  • 6-7.5V - orange
  • 7.5-9V - yellow
  • >10V - white

By the way, you have to tie the colors together. You usually have 3 pins for R, G, B and one for ground.

Through a rigorous scientific process I've determined that 7.5V looks best and provides the best light intensity for the dead of the night.

To use several sensors just wire them in parallel. Any one of them will wake up the light. I've used some CDROM power cables to make the connections.


This circuit will eventually get augmented by an Arduino Nano that will fade-in and -out the light, while also allowing me to use a standard 12V power supply and control each color.

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