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I'm trying to design a low power PIR motion sensor, but there seems to be a dearth of information about it. I know how the pyroelectric sensor works, and I know what the waveform looks like, but how do I make a small, low power circuit that can actually detect that? The ideal thing would be to use an existing chip, but it seems like there are so few of those, none of which are really readily available.

I've found a few circuit diagrams:

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but as you can see, they vary massively in complexity. Ideally I want the simplest, lowest power, smallest one possible, but I'm lost on where to draw the line. The BISS0001 manages to do it at like 50uA, which I feel like I could not get close to.

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You said the ideal thing would be to use a chip. Probably the easiest chip to use is the Zilog ZMOTION series microprocessors, such as the Z8FS040B. These are based off the Z80 microprocessor. They do all of the hard work for you, all you have to do is simply connect the PIR transducer to the correct pins. You'll still need the decoupling caps and the 47k resistor. They also have examples and development boards.

https://www.zilog.com/index.php?option=com_product&task=product&businessLine=147&id=148&parent_id=148&Itemid=77&bk=151&dvc=Z8FS040B

There is also this TI reference design that supposedly has a 10 year coin cell life: http://www.ti.com/tool/TIDA-00489?keyMatch=pir%20motion&tisearch=Search-EN-Everything

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  • \$\begingroup\$ Thanks, those are great. I actually already have an MCU in the system (avr), so I can just use TI's reference design, which is completely specified. The Zilog one is really interesting, but unfortunately I don't have any experience with those and don't at the moment want to learn a whole new toolchain. The only downside of TI's design seems to be that it doesn't have adjustable sensitivity, which would be nice but not absolutely necessary. \$\endgroup\$ – BeB00 Aug 25 '16 at 19:48
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In order to detect a signal as low as 1mV into 47k to drive ~1V into a switch ... You need a variable AC gain of at least 1000x from 0.2 Hz to 60Hz then a full wave rectifier with Sch. diodes , buffer* and driving a holding cap into a low threshold switch or S&H. The buffer* and load cap should have fast attack and slow decay such as 30ms and 30 seconds using FET input OA's and Polyurethane cap with high RC time.

It may be possible with a suitable Dual Op Amp. Note the extra RC filter for the PIR power.

This would be my rough conceptual design strategy. Noise filtering is crucial.

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