Subject:
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Re: Decoding Infrared receiver
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 3 Feb 1999 20:59:31 GMT
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Original-From:
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Darkman <lroska@cyberus=stopspam=.ca>
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Viewed:
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1145 times
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Make sure that your modulating the transmision part with the correct
frequency! When I built my handy board I tested the IR TX circuit and it
gave me 57kHz instead of 40 kHz and I did use all the correct resistor
capacitor values.
I suggest that you check the output freq using a scope and make sure is
whithen tolerance!
-----Original Message-----
From: Tey Chee Beng <cbtey@singnet.com.sg>
To: Handy Board mailing list <handyboard@media.mit.edu>
Date: Tuesday, February 02, 1999 8:13 AM
Subject: Decoding Infrared receiver
> Dear Mr Fred Martin/Friends,
>
> I have been playing with the handyboard for a while now, currently I have
> four handyboards.
> I'm working on the communication module between the handyboards using the
> infrared emitter and the Sharp IS1U60 infrared demodulator. Currently, I
> have this problem, I was unable to sample or decode the data from the Sharp
> IS1U60 infrared demodulator, as the transmission part is OK.
>
> The data transmitted from the infrared emitter is in the form of:
> - 1 Start bit, 8 data bit and 1 stop bit, with a frequency of 400Hz/2.5ms
> for 1 bit (for testing purpose).
>
> As for the receiver part, the Sharp IS1U60 infrared demodulator is used and
> is connected to the port PA2/TIC1. So the excepted data pulses received
> after the Sharp IS1U60 infrared demodulator or at the port PA2/TIC1 will be
> a low pulse (start bit), follow by the data (8 bits), and another low pulse
> (stop bit). When there is no data, the port PA2/TIC1 will always read high
> (logic '1').
>
> (Codes written)
> Interrupt will be generated when there is a falling edge detected on the
> port PA2/TIC1, which is the start bit of the transmitted data. Upon
> interrupt, 68HC11 will wait for 1.25ms, which is about the center of the
> Start bit, and sampled the port PA2/TIC1 for the logic level (either a '1'
> or a '0'). A logic '0' should be read from port PA2/TIC1, but that is not • my
> case, coz I always read a logic '1' at port PA2/TIC1. Does anyone know
> what's the problem ?
>
> The following codes is used to read port PA2/TIC1,
> PORTA EQU $1000
>
> CLRA
> LDAB PORTA
> STD PA2 (PA2 is a two bytes variable)
>
> Even if I read the port PA2/TIC1 immediately in the interrupt subroutine, I
> still get a logic '1' instead of a logic '0'. I have double check with the
> oscilloscope that a logic '0' should be the correct value instead of a • logic
> '1'.
>
> But with the Sharp IS1U60 infrared demodulator removed, and port PA2/TIC1
> short to the ground, a logic '0' can be read.
>
> What is the problem, does anyone ever faced the same problem before ?
> Or is it because port PA2/TIC1 cannot handle a string of high frequency
> pulses.
>
> Any comments on this issue....
>
> Thanks in advance,
> James
>
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