Passive infrared motion sensors: a two-bit camera powered by crystals

I swear one of the best parts of growing up is being able to tear apart stuff without being yelled at

"but I've got a dremel tool with a cutoff wheel so that won't stop me" are fantastic words to live by

Do you mean to tell me that manufacturers made these devices work via the magic of buying two of them?

the disco ball loop pun was 10/10

"Have you ever wondered how one of these works?" Yes... literally this morning

I'm not even joking; I was just talking to my very patient wife and informed her that even though I've seen motion sensors everywhere, I had no clue how they worked. This is the power of this channel.

“You’re glowing today.” Thanks. I needed that.

Very nice work. Greetings from a PIR nerd. Some notes - the hidden "disco ball" mirror array inside some sensor devices are actually an array of parabolas as in car headlights. These are individually designed to focus infrared light from a specific incident angle to the very center of the pyroelectric crystal elements inside the detector. Similarly, the lenses in a fresnel lens-array are also each designed to focus light in the same manner, such that from a selected coverage pattern of incident angles, each has a lens that causes light from that direction to be focused to the middle of the detector. As part of the design process the effective coverage pattern pattern is raytraced with a simple stochastic photon model from the detector crystal elements out and through lenses and/or parabolic reflectors and into the environment. This gives the predicted coverage pattern which conceptually is like a cluster of big chunky and hazy-edged beams of "inverse light" - detection lobes with alternating polarity, a bit like an antenna gain map. We then analyze the predicted performance by passing thermal contrast dummies through these beams which generates simulated waveforms across the detector crystals. Based on this we can tune the design for the intended application - indoor, outdoor, different mounting positions and angles etc.

I have 20+ years experience in engeneering and electrical components, and regarding the pyroelectric cristals, i can happily confirm that IS indeed a letter H printed in them

My favorite use of motion sensors was in the old movie Sneakers. "You can wear this neoprene suit or you can walk REALLY slowly." Turns out, it works. Walk slowly enough and you won't trigger one of these sensors.

Can't believe Technology Connections doesn't have a disco ball!

Waiting with bated breath to see if a can of office duster or a can of tech spray / freeze spray shows up in this video! 😁👍💨🚪

Yes. Yes this is PBS. Or rather, it's better, cause PBS on youtube has sponsors and ad segments. Thank you for doing what you do, doing it so well, and not muddying the pure knowledge with sponsored talking points.

I've been watching your content for years now, and quite frankly, yours is one of the best channels on YouTube. Your videos are always so well put-together and researched, with sky high production values. Here, have a contribution from viewers like me.

The delivery on "We matter, and above absolute zero" was incredible. Batting 100 out the gate

Pretty certain the H is actually a large MOSFET called an H-Gate. The bright H is the gate and the dark squares on the top and bottom are the drain and source. I'm guessing the infrared sensitive material is impregnated onto the h-gate in order to induce a voltage to switch the transistor, which in turn provides enough current to switch the larger one beneath it. The advantage of this design is that you can have an extremely low standby voltage to switch on a relatively high powered device like a floodlight.

Honestly, finding a new video of Technology Connections in my feed feels like getting a present

I used to enjoy demonstrating how a glass window that you could see through with normal vision cameras allowed people to walk past infra red sensors provided the glass was not more than 10’C different (hotter or colder) to the ambient background temperature… and so to get past visible cameras too wear a balaclava and carry a full length glass window from one side of the yard to another without setting off any alarms. Great job!

I very much appreciate that you don't have baked advertisement segments!

As a ~Canadian~ person I enjoy the "This content is in part, funded by viewers like you." trope. Also Thanks to the people who can help interesting channels like yours continue to make good content.