I want to make a motion detection LED strip to the stairs. My idea is to put 5m LED Strip on the wall and put one motion sensor on both sides of the strip (one on the upper level and one on the lower level). I would connect the sensors to the same power supply. Will it work? Connection

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    – FreeMan
    Jun 30, 2020 at 10:50
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    Can you post make/model information for all parts involved please? Jun 30, 2020 at 11:41
  • I don't think this will work. Without knowing more about make/model of the components, I would suspect the power supply would put out something 12-24 volts. Unless you are using motion detectors designed for that, it won't work, most need "real power" to operate. Not only that you have them wired in series, meaning both would have to be tripped before the LED would come on. I have some ideas that would work, like wiring the MD in parallel before the PSU, but I"m not ready to suggest that until I know more about the components. Jun 30, 2020 at 13:52
  • It looks like you're not quite sure how the motion sensors work. The LED strip only has one "hot" feed, so you can't turn it on from "each end" as drawn. You need either to wire the motion sensors' outputs in parallel, or set up a relay as Solar Mike suggests. If that sounds confusing, get someone to come over and show you how to do this. Jun 30, 2020 at 14:32
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    I've got PIR sensor swich (TDL-2023) connected to 12V PSU, and to a LED controller (simple led controller with IR remote). Then the controller is connected to a simple RGB 60led/m strip. I've got only one PIR sensor and have no splitter for PSU yet. I wanted to buy the extra parts if my setup is working in theory.
    – Lac
    Jun 30, 2020 at 14:32

2 Answers 2


I would put a relay between the psu and the led.

Then the relay can be triggered by either of the two sensors or even more.

  • with the PIR module mentioned, an nchannel mosfet would be better as you don't have to worry about coil hold current or flyback; the modules are signal-level outputs, weakly pulled up and common collector pulled down. Rarely do relays work better for DC than FETs.
    – dandavis
    Jun 30, 2020 at 21:15
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    @dandavis found relays work well on dc - seem to be used so often on cars. As for this I was going with something simple that the OP should be able to get to grip with easily.
    – Solar Mike
    Jun 30, 2020 at 21:32
  • fair enough, cars can be quite (electrically) noisy. I just wanted to point out that in every measurable category of performance FETs are better, they are actually simpler to use than relays, and are cheaper to boot. Once I made the switch (haha), I never looked back...
    – dandavis
    Jul 1, 2020 at 0:15

Yeah, that will actually work.

I mean, the way you wired it would be a horrifying hack if it was mains AC power. That would be a “loop”, and those are very bad (in AC) because everything inside the loop becomes inside the core of a transformer.

That’s not a problem in the DC domain. (Mind you I’m not sure that doesn’t change if you use PWM dimming, but I’m not going to tell you to worry about it).

I recommend you bring a 3-wire cable between the two PIRs:

  • Positive
  • Negative
  • Switched Negative (assuming you switch negative; that’s best practice with LED strips).

And then, feed both positive and switched-negative to the LED strip at both ends. That way you are not relying on the thin little pathways inside the LED strip to carry all the current. (There’ll be noticeable dimming if you do).

By the way, learn the fine art of cutting LED strips to length; they have specifically designed cut points.

It will also aid your craftsmanship to learn to splice and/or solder, so you aren’t dependent on cheapie connectors and premade wiring harnesses.

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