im trying to prepare a wiring schema for my home lighting:

  • Lobby sensor should control only lobby led strip.
  • Stairs upper sensor should control lobby and stairs led strips.
  • Stairs lower sensor should control only stairs led strip.

Can I achieve that only with wiring or I need extra relays and when yes then which ones?


  • 1
    This would be a lot easier if + or - were known to be common. Commented Apr 9, 2021 at 21:08

2 Answers 2


You can do this with four diodes:

four diodes added to querent diagram

But you need to find out what size diode part you need to dissipate any heat generated by forward resistance. This will depend on the current used by the LED strips.

This circuit isolates the sensor outputs from each other. If the sensors are tolerant of back-feeding when switched off, you can replace the two diodes marked "*" with wires.

If you can't or won't use diodes, you can use a 12V DPDT relay -- a very commonly available part.

DPDT relay added to querent diagram

Here you can see that when the "stairs upper" sensor is off, the "lobby" sensor controls the "lobby" LED and the "stairs lower" sensor controls the "stairs" LED through the normally-closed (relaxed) relay contacts.

When the "stairs upper" sensor is on, the relay steals the LED feeds from their respective sensor outputs and connects them both to the "stairs upper" sensor output through the normally-open (energized) relay contacts.

  • My one concern with this would be power dissipation in the diodes -- otherwise, this is quite an elegant solution! Commented May 10, 2021 at 3:08

If you're going to use relays, you need at least 2 relays on the output from the Upstairs sensor to isolate that sensor's activation of both LED strips from each other, and the individual activation of the other sensors.

If your sensors don't output 12v with enough current to drive the LED strips, you'd need 2 additional relays for the Lobby and Stair_Lower to switch the voltage directly from the power supply.

This application may be a better use for logic controllers though, as you could use combinatory logic to apply the sensors to the LED strips via a microcontroller, or smart switches on the LED strips driven by smarthome sensors and a controller hub. This gets off-topic for DIY.SE really fast and is a better question for Electronics.SE. Hopefully this information gets you started, at least.enter image description here

  • You're assuming negative ground/common. That's wrong for LED strips, they're positive ground. And once you make assumptions about ground, you don't even need relays: diodes will suffice. Commented Apr 10, 2021 at 0:42

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