Subject:
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Re: Polaroid trouble again
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Mon, 3 Aug 1998 15:16:50 GMT
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Original-From:
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Mark Wallace <MWALLACE@SPS1.PHYS.VT.EDUstopspam>
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Viewed:
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617 times
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I had this same problem when I got mine a few weeks ago. I ended up
putting a capacitor from pin 1 to pin 3 on U2 of the sonar driver board.
I also had to take out the 1k resistor from the BINH. It kept
BINH at 1 V instead of Zero and that seamed to cause problems.
As for the 6 ft problem, it should be closer to 9 ft. I think
the problem there is the IC code you used. If you used the code for
SONAR.C from the HB web site then there is a problem with it. What that
program does is take the difference in time from the internal clock. the
problem is that in the code it says that if the difference between start
time and currnet time is negative too much time has elapsed. Well, this
has a 16 bit counter so when the difference is greater the about 32,700 it
becomes negative. If you do the math, that means at about 9 ft that
happens so it tell you you are out of range.
The way I fixed this was to slow the clock down.
I looked up information on the motorola web page and found where the
prescalers were for the clock.
If you want to slow it down by a factor of four you can just add
this line to you program in sonar_init()
bit_set(0x1024, 1);
I believe bit_set(0x1024, 2); will slow it down by a factor of 8 and
bit_set(0x1024, 3); will slow it down by a factor of 16.
There are better ways of fixing this problem but they appear much
more complicated. For example the motorola chip has an overflow flag that
says when the internal clock flips. You could incorporate that into your
code instead of slowing the clock down. Good luck and I hope this helps.
Mark Wallace
e-mail mawalla3@vt.edu
mwallace@sps1.phys.vt.edu
Web page http://sps1.phys.vt.edu/~mwallace/index.html
"What a waste it would be after 4 billion tortuous years of evolution if
the dominant organism contrived its own self-destruction"
Carl Sagan
On Mon, 3 Aug 1998, Alf Kuchenbuch wrote:
> Hi!
> I am having trouble with my Polaroid sonar:
> When I keep my HB hooked up
> to external power, I will only get correct readings up to 20 inches. As
> soon as I use battery power without hooking it up to external power, the
> readings are correct up to 6 feet, not more! This sound like EMI, I
> guess. I tried all the capacitor tricks from HB mailing list, but in
> vain. Do you know a fix that works?
>
> Alf H. Kuchenbuch
>
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Message is in Reply To:
 | | Polaroid trouble again
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| Hi! I am having trouble with my Polaroid sonar: When I keep my HB hooked up to external power, I will only get correct readings up to 20 inches. As soon as I use battery power without hooking it up to external power, the readings are correct up to 6 (...) (26 years ago, 3-Aug-98, to lugnet.robotics.handyboard)
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