I'm working on a little project robot on my own that I would like to
make chase people/animals, so I figured PIR would be a good method of
finding some warm blooded prey. I have some cheap PIR sensors (the
elements themselves, crystal on the front of a 3 lead metal can) from
electronics goldmine. Ive been wondering how I'm supposed to monitor
or interface the sensor.


Ive figured out that pins 1 and 2 are the output FET, and pin 3 is the
'ground' connection, Ive kept 2 shorted to 3 and I have managed to
make it work, but nothing useful quite of yet. With a 10k resistor in
series with the device between pin 1 and the 5v supply, I could take
the voltage from pin 1 and send that to a comparator to get it to
blink a LED when I moved my soldering iron about 1" in front of the
element. Not quite as sensitive as I was hoping...

Trying out other resistors, I found out that it would draw around 800
uA or so without depending on the resistor much. Seeing that, I took a
constant current LED tester I made, dialed down the current to 770 uA
(resolution was kind of lacking on the 10 turn pot since it normally
runs at ~20 mA...) , and put the sensor in it. I meter the voltage
across the sensor, and its slowly oscillating between ~.5 v and going
rising, up to varying values from 2.5 volts to up to 4 volts.  The
change in voltage was slow at first, then quickly once it got to >2v.
The oscillations were slow, taking about 10-20 seconds to go though a
whole cycle.

Ive read about PIR sensors needing time to 'warm up' or to 'balance'
upon turn on, so I let it sit for 2-3 minutes. After letting it sit
for a bit, I measured the voltage again, it was going up to 10v on
some occasions, others were only 5-6v All with the crystal pointed
away from me, at what I would expect to be a pretty static view for
it.

Any guidance on how to work with the PIR?

Or heck even for that matter, any idea how to make a small robot
follow/chase a person? Or even just something neat to make the small
robot do. I'm hoping to build this as a base for experimentation, so I
if I can come up with something better than making one follow a
person, I'll go for it.

Thanks,
Jonathan Hallameyer
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