Subject:
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Re: Lost my IR Tower
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 14 Feb 2002 23:41:53 GMT
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Original-From:
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PeterBalch <peterbalch@&StopSpam&compuserve.com>
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Viewed:
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640 times
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Stef
> Why did you remove the IR diodes ?
The IR LEDs are pulsed on and off at 30kHz - that's on top of the 2400bps
serial signal. I had to remove that 30kHz signal.
That's what the 100nF (on the base of the transistor) is for.
The time-constant of the 100nF and the 470R has to be just right. If the
100nF is too big, the 2400bps deteriorates. If the 100nF is too small, the
30kHz gets thorugh to the PC and confuses its UART.
The RCX pulls the base of the transistor down and the 470R pulls it up. If
I'd left in the IR LEDs, they would also pull up the base of the
transistor. I wasn't sure how that would affect the time-constant.
I dare say you could get it to work. Leave the IR LEDs in and remove the
470R. Then adjust the 100nF value until you get reliable comms with the PC.
> It would even be nicer, if also the IR-sensor could be left in place, but
I don't know the Lego circuit.
Neither do I. I assumed that the IR receiver would be driving its output
both high and low (rather than a pullup or pulldown resistor). I removed it
so that my circuit didn't have to fight with it. Try leaving it in and see
what happens.
Peter
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