I am looking to create a simple circuit to control a couple LED light strips inside a cabinet using two reed switches that turn on the lights if either or both doors is open and the lights to be off if both doors are closed.

Door 1  Door 2  Light
Close   Close   Off
Open    Close   On
Open    Open    On
Close   Open    On

Thank you in advance for any advice or suggestions!

  • \$\begingroup\$ You are causing some confusiont - see the two answers below. Are the switch contacts closed or open when the door is closed? \$\endgroup\$ – Transistor Oct 22 '17 at 17:21
  • 1
    \$\begingroup\$ What is powering your LED light strips? (Are you creating/selecting a specialized power supply here or is it provided for you by the LED strip vendor?) Can you provide a link to the strips you are using? \$\endgroup\$ – jonk Oct 22 '17 at 18:40
  • \$\begingroup\$ I have not been specific on what my materials will be as I have not purchased them yet. I am still in the planning stages and wasn't sure if this was possible. I kept finding 3 way switches in my research and knew that wasn't what I was looking for. I imagine that I would mostly be getting a normally open reed switch. \$\endgroup\$ – CampSoup1988 Oct 23 '17 at 2:40
  • \$\begingroup\$ I will be getting 2 or 3 light strips each about 1-1.5 feet long, I do not have a specific light strip picked out yet. I cant decide if I will be running it off of an outlet or battery yet. Battery makes it more compact, but with outlet, I don't need to worry about replacements batteries or the voltage being too low. \$\endgroup\$ – CampSoup1988 Oct 23 '17 at 2:51

simply connect the two switches in parallel, like so:


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Same mistake as me. S/he's got NC switches and so needs a NOR function. \$\endgroup\$ – Transistor Oct 22 '17 at 16:43
  • \$\begingroup\$ @Transistor: I don't see any mention of the type of switches, only the states of the doors. For my circuit, the switch must be open when the door is closed. \$\endgroup\$ – Peter Bennett Oct 22 '17 at 17:17
  • \$\begingroup\$ Ha! I'm reading open / close as the state of the contacts! Let's see who's right. \$\endgroup\$ – Transistor Oct 22 '17 at 17:20
  • \$\begingroup\$ @Transistor: As I think more about it, the reed switches should be NC. Closing the door would place the magnet close to the switch, causing it to open. Opening the door would remove the magnet, allowing the switch to close, and turning on the light. Very confusing, this logic stuff. :-) \$\endgroup\$ – Peter Bennett Oct 22 '17 at 18:01
  • \$\begingroup\$ No, as far as I know the reeds pull together when magnetic N-S + N-S is induced on each reed. They're closed with the magnet. Changeover versions are available, however, so open with magnet must be possible. \$\endgroup\$ – Transistor Oct 22 '17 at 18:07


simulate this circuit – Schematic created using CircuitLab

Figure 1. A logical NOR arrangement of two switches.

What you have described is a logical NOR function. This is easily achievable by parallel connection of the two switches and a transistor to invert the signal.

If either switch is turned on current will flow into the base of the transistor and turn it on allowing current to flow between the collector and the emitter.

You haven't specified the voltage and current and exact component values depend on those parameters.

  • \$\begingroup\$ I did not think of putting the switches in parallel. I am new to circuitry and I kept finding 3 way switches when I tried to research a solution, and knew that wasn't what I had wanted. As I stated in a comment on my original post, I did not post any exact values/components as I am still researching the project before I started to buy the supplies. \$\endgroup\$ – CampSoup1988 Oct 23 '17 at 2:55
  • \$\begingroup\$ You'll need to figure out how much current the LEDs require. Reed switches can't handle much so the transistor arrangement is better in that regard because only a little current is required for the base of the transistor which then switches the LEDs. \$\endgroup\$ – Transistor Oct 23 '17 at 7:53
  • \$\begingroup\$ Two of the light strips that I am considering are Adafruit's Cool White LED Weatherproof Flexi-Strip 60 LED - (1 m) and Analog RGBW LED Strip - RGB plus Warm White - 60 LED/m - ~3000K (Using just the white for this project). Adafruit sells their LED strips in 1 meter increments, so I would probably buy just 1 meter and either split the strip into 2 1.5 foot strips or 3 1 foot strips. \$\endgroup\$ – CampSoup1988 Oct 23 '17 at 19:33
  • \$\begingroup\$ They should have a mA/m spec or you should be able to work it out from the full length. \$\endgroup\$ – Transistor Oct 23 '17 at 20:02
  • \$\begingroup\$ The specs for the first one states Maximum 12V @ 60mA draw per strip segment Max 1.2 Amps per meter (all LEDs lit full brightness) \$\endgroup\$ – CampSoup1988 Oct 24 '17 at 1:48

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