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I need to trigger a peripheral on my existing PCB design. I would use a pushbutton, but can't remake the boards. I need to hack/modify a way in.

My MCU is An ATMEL XMEGA and I have a PIR detector using a NCS36000 controller. This is currently used for another function, and I would like to keep it. Is it possible to utilize this as a replacement for a pushbutton, I.E. remotely trigger the PIR sensor in a unique way?

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closed as unclear what you're asking by brhans, Andy aka, PeterJ, Daniel Grillo, nidhin Feb 2 '16 at 15:11

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ I read it twice and have no idea what this question is about. \$\endgroup\$ – Andy aka Feb 1 '16 at 17:39
  • \$\begingroup\$ I have edited this to make it bare facts rather than background on the project. I hope that helps as this is a good question. \$\endgroup\$ – mcmiln Feb 1 '16 at 17:55
  • \$\begingroup\$ By PIR do you mean a Passive infra-red movement detector? With a relay built in? \$\endgroup\$ – Steve G Feb 1 '16 at 18:29
  • \$\begingroup\$ It depends on the actual schematic and code you have. How is the PIR sensor connected? How easily can you modify the code to prevent false positives? \$\endgroup\$ – Passerby Feb 2 '16 at 0:10
  • \$\begingroup\$ Based on electronics.stackexchange.com/questions/65436/… you won't be able to trigger it via IR leds easily. Hacking a diode OR circuit to the PIR output may be the easiest method. Cut a trace, add the circuit, change your code to adjust. \$\endgroup\$ – Passerby Feb 2 '16 at 0:18
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Remotely triggering a PIR sensor, or it's controller, via IR signals is not a feasible option. PIR sensors are designed for human body heat ranges, and motion across zones, over time/states. See Can I electronically trigger a PIR motion sensor? for info on that.

Since your board is already designed, and assuming that you have no other inputs available, you are trying to turn the GPIO defined for the PIR sensor as an input for multiple things. This can be done, but it will require some hacking.

The NCS36000's OUT (or LED) output is a 10mA max push-pull output. I am not sure if you are using the xLED_EN pin, so let's assume you aren't. Also assuming it's directly connected.

Use a Diode OR pair. Since Out is active high, this works well.

schematic

simulate this circuit – Schematic created using CircuitLab

If you want a unique signal, if your input is a ADC capable pin, add a pull-up to the switch, so you create a voltage divider. A voltage lower than the PIR OUT's level would mean it's the button.

Or connect any active high circuit to the switch instead. A 555 Timer in one shot mode, or another microcontroller. As the PIR sensor only pulls OUT high based on motion, for a fix amount of time, a set of multiple quick pulses or even a single quick pulse would signal that it's the button. The PIR sensor takes priority. You will need a timer or polling to keep track.

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You can reliably trigger all single-sensor PIR modules reliably with an FRS/GMRS radio transmitter. So long as your PIR sensor isn't shielded, or one of the really nice multi-zone types, all you have to do to use it for a momentary-on pushbutton is key (push the talk button on) a cheap "walkie-talkie" style radio (available at just about any outdoor-type store).

(Yes, I have tested this fairly extensively; anything from FRS through 950MHZ works pretty reliably, but IIRC about 725MHz wlrked wkth the lowest output power needed per distance).

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  • \$\begingroup\$ For an interesting trick, set your FRS radio to "VOX" mode (voice activated keying) and you can trigger your setup by sound..... "clap on..." \$\endgroup\$ – Robherc KV5ROB Feb 2 '16 at 2:43
  • \$\begingroup\$ This seem dubious. Any source for this? \$\endgroup\$ – Passerby Feb 2 '16 at 3:19
  • \$\begingroup\$ Sorry Passerby, as "cliche" as it sounds, any documentation on the experiments I was conducting at the time aren't "available for public consumption" due to the nature of the project involved. However, I can say that while researching other PIR devices we discovered that the mfgrs were aware of this and had started marketing "rf shielded" units for use in areas where cell phone usage was causing false trips. Here's a source from a quick Google: forum.allaboutcircuits.com/threads/… \$\endgroup\$ – Robherc KV5ROB Feb 2 '16 at 3:23

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