Inside a pyroelectric sensor - PIR dissection

[@Bandrik]

I really enjoyed this. I was taking apart a light that has a motion detector that turns on when you walk by it. I was curious what was inside the PIR module, and now I know! Thanks!

[@keithbrian6974]

I like watching videos of those curious enough to take time to discover things. I am fairly sure the metal pads under the sensor are for either heat sinking or electrical grounding (prob for both). Cheers and keep discovering!

[@keithbrian6974]

This is likely just a PZT (Lead Zirconium Titanium Oxy-combo) crystal-polarized film, where the 8 pin is a current integrator, measuring the capacitance of the polarization of the PZT crystal using electrodes on both sides of the film. The silicon cover is perfectly OK as it allows the frequency of IR through it; so probably just protects it. These types of crystalline structures change polarization depending on heat due to a high pyroelectric constant (ie. change of polarization, or charge as a capacitance, depending on a small change of temperature). Imagine doing this with a matrix of 64x64 or greater, monitoring the IR heat change per pixel. Math and equations are one thing, but sometimes learning requires mates tearing things apart to understand. And when they share, we all win! Cheers!

[@nameismetatoo4591]

1:35 The EOL resistors aren't for detecting when a sensor is cut (as the loop resistance would jump to infinity regardless of whether a resistor was there or not), but for short-circuit detection. If someone tries to bypass a door sensor for example by bypassing the reed switch with a jumper wire, the panel will be able to see the sudden increase in current through that zone. That chip at 3:18 looks like a photocoupler, but I'm not 100% sure. It would make sense, as electrical isolation is important for reliably detecting small changes while avoiding false alarms caused by noise. Two of the pins go to an internal LED, while the other two are for the photosensitive switch. When the LED is on, it closes the switch while remaining electrically isolated from the circuit that it is switching. The window on the pyroelectric sensor, if I had to guess, is probably some kind of germanium alloy. Most materials clear to visible wavelengths actually block IR. Germanium works as an optical bandpass filter, allowing IR to pass but blocking shorter wavelengths. It's the same material used for the lenses of thermal imaging cameras. It could also be made of some kind of polymer with an embedded filtering material, as there is really no need for it to bend light like a lens but simply filter out the unwanted wavelengths.

[@mdtarikulislamrion9389]

great video, Thanks a lot

[@alphonsesynrem28]

Thank you for this nice video. Now I think they do have any complex digital chips and just a mosfet or similar transistor and resistors. So it can be hacked for other purposes also. So the whole comparator system is outside on the board. I am wondering if it's output will be stable or stay stable to certain temperature. Will the output be steady or will it give output if an object is not in motion. Thanks again, I will try to get to this experiment and see what comes out.

[@randomtronic]

Thanks This was a very old sensor, newer ones must be more integrated I would think.👍

[@SLYKER001]

thankyou for opening it skip to 12:13 sensor where opened i think this "glass" made out of germanium, heard that pure germanium clear for IR light

[@msylvain59]

The 15-25 Kg jumper is writen "pet" it must be for pet-tolerance system of the alarm system.

[@randomtronic]

Yes, indeed! Somehow when I looked at word 'pet' on pcb I didn't think it could be about an actual pet, and automatically assumed it was some kind of technical acronym :) Thanks

[@mickaelcabrillas6326]

That is a pyro...its expensive and the things inside its chips

[@MrSpock-sm3dd]

This video could have 5 minutes.

[@randomtronic]

Mr. Spock agree. I'm learning hopefully :)