Subject:
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Time measuring problems
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 8 Apr 2000 16:12:21 GMT
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Original-From:
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Adam Oliver <oli@wantreeIHATESPAM.com.au>
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Viewed:
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882 times
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Hi all,
I hope someone out there can help me with this, I'm going nutz (actually i
think i'm already there).
I am trying to measure a short period of time. Ultimately this will measure
ultrasonic ping/echo using Kam Leang's ultrasonic circuit. Right now I just
have a 555 timer in monostable mode trying to get it working. I have the 555
working fine using various RC values, and I trigger it using the SPI port
(SS pin I believe). The "echo" is fed into digital input 7 (i believe that
is TIC3?)
I have used the sonar code on the handyboard web site and changed it to do
the job. I am getting no consistent readings.
With no output from the 555 (ie LOW, checked with multimeter), the reading I
get from typing digital(7) is 1. Am I missing something? I would have
thought this should be 0. If I put a wire between the input and +5V, the
value read from digital(7) is 0. It seems to me that these results are
inverted. Could I have done somethign to the board?
Assuming these values are correct, I use
bit_set( 0x1021, 2 ); bit_clear( 0x1021, 1 );
and
bit_set( 0x1021, 1 ); bit_clear( 0x1021, 2 );
to set for rising or falling edges. I only use one at a time, but I tried
both just in case.
Regardless, the values I get are completely random. Here is the rest of the
code I am using. (Sorry, I hate pasting so much)
**********************
void ping()
{
poke( 0x1008, 0x00 );
msleep(5L); /* this generates the pulse to
trigger the 555 */
poke( 0x1008, 0x20 );
}
void init()
{
bit_set( 0x1009, 0x30 ); /* Set pins SS &
SCK for output */
bit_set( 0x1021, 2 ); bit_clear( 0x1021, 1 );
}
int son() {
int start_time;
poke(0x1023, 1); /* clear tic3 flag */
start_time= peekword(0x100e); /* capture start time */
ping(); /* trigger pulse */
while (!(peek(0x1000) & 0x1)) { /* wait until receive echo */
if ((peekword(0x100e) - start_time) < 0) {
/* if too much time has elapsed, abort */
bit_clear(0x1008, 0x00);
return -1;
}
defer(); /* let others run while waiting */
}
poke(0x1023, 1); /* clear tic3 flag */
return peekword(0x1014) - start_time; /* tic3 has time of echo */
}
***************
Can someone tell me what the line "while (!(peek(0x1000) & 0x1)) " does? I
know it waits for the echo, but what are those bits doing?
Any suggestions on what I could be doing wrong would be GREATLY appreciated.
Unfortuanly my understanding of the bit-level processes are fairly limited,
so I'm having a bit of a hard time with this.
Thanks in advance
Adam
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