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Subject: DPRG: no subject (file transmission)
From: David Philip Anderson dpa at io.isem.smu.edu
Date: Wed Jan 14 00:33:12 CST 1998

howdy.


jgbrown writes:

> Hey, that's pretty close to our motto:  It's not as easy as it looks.

I like that!

> By the way, I thought your robot was great (that I saw on the video).

thanks.  thought I might bring it if I'm able to get to the DPRG meeting
in Dallas on Saturday.

> How do you hook up and interface the motion detectors?

The motion detectors I got from Tanner's (like most of the bot).  They came
without documentation in a plain white cardboard box.  On the back side it
says "elf atochem"  and "PIRM 180-200 Motion Detector Module."  There are
four pins labeled "A  D  -  +"

I hooked "-" to ground and "+" to 5 volts, and looked at the other two pins
on the 'scope.  The "A" pin is obviously an analog voltage that wanders around
near ground and I never have been able to make much sense out of it.  The "D"
pin is a nice robust digital signal that goes from low to high for a few 10ths
of a second when the module "detects."  It seems to take a while, 3 or 4 seconds,
for the module to stabilize in a given space before it stops triggering.  I'm 
guessing that it is some adaptive adjustment to the local background IR.  After
that it fires off when mammals move thru it's field of view.  I've tried throwing
objects in front of it, but it only seems to trigger when a suitable IR
emitter (the cat) passes by.

The "D" pin is a natural digital input, but I happen to have a bunch of 8 bit
A/D ports (32) on the MIT 6.270 board, so I used one of those and in software
I test to see if the input is above or below 128 (i.e., is hi bit set?) 

It won't work when the bot is in motion, (constant detections) and apparently
can't see thru the Plexiglas front bumper, which must be opaque at the required
IR frequency.  So I mounted it on a servo arm and elevate it above the bumper
when the bot goes into motion detection mode.

The current behavior is to stop the bot, do a 360 degree scan to determine
where mammals are likely to be (a combination of sonar distance, active IR
object detection, and photo brightness) then orient in that direction and
raise the motion detectors.  Wait 3 seconds for adjustment, then arm.   In
it's present enlightenment, it tries to lunge in the direction of the motion
detector that fires first, or straight forward if they both go off.  This
works correctly about 75% of the time.  

I seem to be having a new problem lately with random triggering of the detectors,
perhaps digital noise on the supply lines?  Also, of the three detectors I
originally purchased, one stopped working early on, I may have damaged it while
messing around with the connections.  I can't remember what I paid for them,
they were pretty cheap.


cheers
dpa

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