PIR sensor behind glass?

[yo-less]

@dmcinnes Thanks for your link, I’m using a radar module in a Pi-independent LED lighting control unit that a friend of mine put together (So I have no clue how his circuits actually work, but they do and that’s great :D), which is why my first impulse was to use a radar motion detector as well.

I couldn’t find any that operated within the voltage specifications of the PI’s pins. Your link lists a working voltage range of 5.5 - 18 V DC, but the Pi only offers 5 V DC, doesn’t it?

So are you planning on using an external power source for your module?

[dmcinnes]

Hmm I’ve seen othe specs that say working voltage is 3.3-20VDC… hopefully that’s more accurate. In any case I’ll try it with the 5V from the PI and go from there.

[dmcinnes]

@yawns I’ve read that microwave sensors will work behind glass, but I’m not sure if it will work behind the semi-mirrored surfaces we’re using.

[yo-less]

@dmcinnes It’s great that you’re experimenting with this in any case. Please let us know the outcome once the sensor has arrived.

[KirAsh4]

To anyone asking: ‘working voltage’ just means it will work with voltages within that range, so from as low as 3v3 up to 20v.

[yo-less]

Alright, everyone. I said I would start experimenting with the PIR sensor and experiment I did.
So first of all we started drilling a hole of diameter 8mm into one side of a piece of wood
(we went 5mm deep as this corresponds with the height of the cylindrical sensor):

This is not all we did, as you can see, we also drilled a hole of diameter 3mm on the other side,
but this time we made sure it went all the way through:

Next, we removed the Fresnel lens from the sensor:

After that, we put the sensor in the bigger hole which perfectly houses the whole cylinder:

Then we waited to see whether the mirror would turn itself on if we moved past the piece of wood.
And, hooray, it did!

Emboldened by this discovery, we started all over again, but this time with smaller holes on the other side,
so we ended up with this setup:

Simply ignore the rubber band, it’s there to hold the circuit board in place :)

Anyway, here’s the good news: The mirror recognizes somebody walking by if the hole is as small as 2 millimeters in diameter.
It did not work with a 1mm hole, but hey, are we living in a perfect world? :D

Anyway, this solution is good enough for me, we will drill a 2mm hole in the bottom center area of the mirror frame and hide the sensor behind it.
I’m thinking we might even be able to make the hole less apparent by choosing a piece of wood similar to the one above
with some nice-looking wood grain and / or knots.

[cowboysdude]

That is awesome!!! Great job and Thank you for the info!!!

[dmcinnes]

I got the microwave radar modules today!

They work great, even behind my mirror, although they are very sensitive. It triggered on even small arm movements and didn’t require line of sight. Works for my needs though, I just want it to turn off the monitor when nobody is around.

I haven’t tried powering them with my PI, but they worked fine with an external 5v power supply.

[cowboysdude]

That’s another great way to do it! :) Where did you get them from?

[yo-less]

@dmcinnes It’s great to hear that they’re working on an external 5v power supply, this means it should be possible to use them on the Pi. It would be really nice if you could try hooking them up to the Pi to see if they’re acting up once attached to the Pi’s pins. I’ll probably try to get one as well if you can confirm they’re working on the Pi as well.