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I saw this question and I think I have a similar problem/question.

I have:

  1. IP Camera, DCS-7010L, 5 V, 1.2 A

  2. PIR, HC-SR501 (like the one of Kudos@Dave ... I think), 4.8-20 V(dc) input, 3.3 V output

I connect the PIR to the alarm (DI/DO) of the camera, without any transistor or similar, and it is OK.

But, the question is: can I connect 2 or more PIRs to the DI/DO of the camera in parallel as shown?

proposed connection diagram with two PIRs in parallel

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    \$\begingroup\$ I am surprised this was closed, as it relates to design. \$\endgroup\$
    – Bort
    Jun 19, 2018 at 12:01
  • \$\begingroup\$ @Bort Connecting ready-made modules to a ready-made camera is hardly design. How is this different from e.g. "Can I connect my USB2.0 mouse to a USB3.0 laptop?" kind of question? (except that a question about standard interfaces like USB can actually be answered without guessing) \$\endgroup\$
    – Dmitry Grigoryev
    Oct 26, 2018 at 10:45
  • \$\begingroup\$ @DmitryGrigoryev - Your USB example is a question about forward compatibility with a particular standard...Which I dare say is still related to design. There are many power/data protocols/buses with variations that may or may not work together, and a designer may wish to know which protocol to use for their project. Regardless, this PIR question asks if two logic signals can be combined in parallel. The answer involves adding three additional components. The question may seem awfully simple to you, and may even have been asked here before, but don't forget that you were once a novice as well. \$\endgroup\$
    – Bort
    Oct 26, 2018 at 11:23
  • \$\begingroup\$ @DmitryGrigoryev - Also consider that questions about component identification, methods of soldering, and "My multimeter probes are too big to measure a laptop battery" are apparently on-topic here. How is a question about (multimeter probe size) any what more about design than OP's PIR logic signal question? \$\endgroup\$
    – Bort
    Oct 26, 2018 at 11:23
  • \$\begingroup\$ @Bort It's not about how simple/complex the matter is. If the question included the schematic of the PIR sensor, we could tell how to combine the signals properly. If a device is a black box, the only way to correctly answer the question is to read the manual, at which point it's a usage question. The current answer makes a guess that combining PIR signals may require diode OR circuit, but there's no evidence that it's actually needed. An answer suggesting to connect them directly could just as valid. Don't you see a problem with a question to which two contradicting answers are both valid? \$\endgroup\$
    – Dmitry Grigoryev
    Oct 26, 2018 at 13:01

1 Answer 1

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You cannot simply put the PIR modules in parallel to your camera's input. The PIR modules provide a logic level signal, and putting them in parallel would cause the modules to short circuit each other's output.

In the simplest case, you could use a diode OR circuit to allow the PIR modules to drive the camera input either high or low. Unfortunately, I am having some trouble downloading the camera handbooks so I don't know whether you need to drive the input high or low.

Depending on what the camera needs:

If a low signal means start the camera, use diode OR with the cathodes towards the PIR modules and a pull up resistor on the camera input.

High signal means start the camera, use diode OR with the cathodes towards the camera, with a pull down resistor on the camera input.

Diode OR on Wikipdia.

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