From: Mark Simpkins
Subject: Need help measuring pulses from Polaroid 6500
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NNTP-Posting-Date: Wed, 13 Nov 2002 21:42:05 EST
Date: Wed, 13 Nov 2002 21:38:15 -0500
I recently got a Polaroid 6500 ultrasonic detector kit from acroname
and am trying to work out a simple design with it. I have it set up
on a JE25 breadboard, and I'm pulsing the INIT line with a 10Hz square
wave, the maximum you can pulse it. When it detects an object, the
ECHO line goes high and from what I can tell if I measure the time
between the INIT going high and the ECHO going high, I'll have the
roundtrip time and I can divide by 2 to get the time-distance to the
object. Ok, so far so good.
What I'm having problems with is the counter part of all this, and
latching & resetting it with each successive pulse. I'm not well
versed with PICs, so I'm just using digital logic parts, a 74LS590 to
be exact. I'm clocking the 590 at 10kHz, on both the count clock and
register clock lines, and then outputting that to two 7 segment LED
display decoders that gives me a decimel interpretation of the count,
or at least thats what I'd like to do.
Unfortunately I can't get it to work properly and I think I may be
going about it all wrong. I would just like the counter to start
counting the 10kHz clock as soon as the INIT line goes high, and stop
as soon as the ECHO line goes high. Then when INIT goes to its low
state, the register resets and the process starts over again. Ideally
the register would just put numbers out like 30, 45, etc etc that
indicated the total number of pulses between INIT and ECHO, and do
that 10 times/sec according to the INIT pulses. Am I crazy, or am I
making this too complicated?
Any help/pointers/circuits would be greatly appreciated.