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Registered Member #97
Joined: Thu Feb 09 2006, 05:40PM
Location:
Posts: 61
I took a PIR sensor ( PIR d203b datasheet ) from an motion sensor switch and I have been goofing around with it. I hooked it up as follows: Drain to +5V, ground to ground, and source to DMV with a 1M ohm resistor from source to ground. After turning on the power it takes a while to settle to around .91 V or so. If I put something kinda warm infront of the sensor, like my hand, it drops about a tenth of a volt or so and the returns back to near .91V. When I remove my hand the voltage goes up a similar amount before return to the steady state. Something really hot makes a larger increase.
I have a few questions: 1. What is the purpose of the resistor between the source and ground (the datasheet circuits all have a 47K ohm resistor) 2. Why does the voltage change and then return to the steady state? It is still looking at the hot thing?
It is kinda fun. You can point it at things and tell if they are really hot or not... very useful
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
If you get hold of a cheap make-up/shaving magnifying mirror, - a few £ on ebay - and set your sensor up at its focus, as in a reflecting telescope, you'll be surprised at the increase in range and sensitivity.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
An even more interesting hack is to make a "Chopper" using a pager motor with its weight replaced with a vane. This will when correctly RPM adjusted allow you to make an effective linear PIR sensor. I would expect around 3-400 rpm from such a setup, those cheap "heat vision" scopes often use something like this or the electronics variant of pulsing the power supply to help compensate for a lousy sensor.
I am in the process of seeing if this works with LCD panels taken from broken PS3 optics, as they are easy to find and a heck of a lot lower power.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I just thought of a possible explanation for the 47k resistor. The sensor might have a FET source follower built in to buffer it, like an electret mic. The 47k resistor would be needed to bias the FET.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
Conundrum wrote ...
But would the ps3 optics idea work?
It won't. The long-pass filter of the detector flattens everything shorter than 5500nm to zero. Even if the optics were made of fused silica, the optical window would be limited to <4000nm.
One of the few things that might work is the MEMS mirror array of a DLP projector embedded in some fancy infrared optics system.
But then again, you might also consider such contraptions:
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PIR sensor fun
