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

Not that kind of crystal.
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[rocbolt]

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

[shoy]

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

[JamesRibe]

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

[redundantqwail]

The delivery on "We matter, and above absolute zero" was incredible. Batting 1, 000 out the gate

[michaelcalvin]

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.

[GlassFoxGear]

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.

[ArrowNought]

"Motion sensors, you've seen them., "
Which made me think the next line would be:
"And they've seen you too"

[mackpines]

“You’re glowing today.”

Thanks. I needed that.

[runaway]

I like how the end of this one had a PBS style "this show was brought to you by viewers like you. Thank you." It really added to the whole "mini documentary/educational tv" vibe your channel has to it.

[barsa]

The way he timed his paragraphs to end each seven seconds to exactly match the loop of the disco lights is amazing, he also mananed to squeeze a joke in it. I just love the detail and the incredible amount of work and planning he puts even on simple explanations

[ihavetwofaces]

3:49: Elmo says: "today's ability to detect people moving in a room is brought to you by the letter H".

[KanalFrump]

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.

[A.X.]

Thanks for the “thermal positivity” today. I’m glad that I’m not an “absolute zero” and your reminder of my “potential” warms my heart…

[OrphenStudios]

I found your channel a month after I lost my dad cancer during a nearly two week period of no electricity due to a tornado. I was in my car charging my phone and feeling absolutely dead inside when I found your videos on televisions. Been a fan ever since. You helped get me through a bad time. Thanks for all the videos. Your work has impact!

[armin]

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

[pufthemajicdragon]

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.

[HnD]

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

[Jyodann]

Really entertaining presentation of many of the daily items we take for granted! Truly awesome content :D

[ramiroolarte]

I have 23 years of field experience with home security, and it's the first time I truly understand how these things work.
I guess i must thank no one ever asked me too much about it... But now I'm prepared hahaha...

[bassmanbuck]

"Have you ever wondered how one of these works?"

Yes... literally this morning