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PIR Amplifier and Hack

Turn differential PIR sensors found in motion switches into ones providing analog output

filip-mulierFilip Mulier
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PIR sensors found in motion switches are differential, so they can detect differences in infrared energy and trigger a switch. They have two sensors connected electrically back to back. If you block one of the sensors, it is possible to measure the IR level directly with the right amplifier circuit. This can be used to locate people, using an RC servo to scan and look for peaks.

PIR Amp opt.sch

sch - 250.84 kB - 02/03/2018 at 12:43

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PIR Amp opt.brd

brd - 36.23 kB - 02/03/2018 at 12:43

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equinitry wrote 02/05/2018 at 14:49 • point

anyone tried to make a aluminium parabolic mirror centered with a PIR sensor? should increase response and distance extremely

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agp.cooper wrote 02/03/2018 at 14:29 • point

Hi Filip,
I hate to point out some problems with your design.

The first is the typical gain for a PIR sensor amplifier is x3000 rather than x100 (but if your using an ADC then maybe you will get away with it). There are some excellent worked examples for PIR amplifiers on the Internet.
The second is that the field of view of a naked sensor is in the order of 140 degrees. So very limited range (perhaps one foot) unless you use a lense or some other method of restricting the field of view.

Anyway, if you interested, have a look one I built (https://hackaday.io/project/29585-little-monster-scanner). I stayed with a differental sensor setup and has a range of about 4m. The field of view was about 10 to 15 degrees.
I have tried the MLX90615 heat sensors but with limited success.
AlanX

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