Subject:
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Re: Tasks vs. program slots
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Newsgroups:
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lugnet.robotics.rcx.nqc
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Date:
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Sat, 18 Sep 1999 20:19:13 GMT
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Viewed:
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2379 times
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In article <37E32DDB.2AEF99CA@iname.com>, Nick Taylor <ntaylor@iname.com> wrote:
> I've been wanting to use a Sharp IR receiver to demodulate the signal
> from a LEGO remote control, and then a PIC to decode the rx output
> for use by an external controller (not the RCX). Would you please
> give me a little more of an explanation of the remote's transmitted
> signal ... comm protocol, timing, etc. My lack of knowledge is
> keeping me from making any sense out of what I see on the 'scope
> coming out of the Sharp IR receiver.
What exactly does the Sharp IR receiver do? If it uses Sharp's ASK
modulation, then you may have a problem. Ideally, what you want is
something like a phototransistor to a good preamp, followed by a bandpass
around 38kHz, then some sort of detector (e.g. a comparator). You'll also
need some sort of AGC control to bias the preamp and/or detector.
Lego's IR protocol uses a 38kHz carrier. Bytes are encoded using standard
serial NRZ encoding at 2400 bps using 1 start bit, 8 data bits, odd
parity, and 1 stop bit. An RS-232 '0' bit corresponds to sending IR, a
'1' bit is nothing. This means that idle doesn't send anything. You
should see a bit-time's worth of IR as the start bit, then the 8 databits
(lsb first), then a parity bit, then at least one bit-time of stop (no
light).
I'm going from memory here, so bear with me if I messed up the polarity of
anything. Hope this helps.
Dave
--
reply to: dbaum at enteract dot com
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Message has 2 Replies:
 | | Re: Tasks vs. program slots
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| (...) The Sharp GP1U581Y is a 38kHz receiver that incorporates an amp, a limiter, a bandpass filter, and a demodulator ... outputs a low while receiving an IR signal, a +5V high when not. It does NOT do any decoding. (...) From what I've been seeing (...) (25 years ago, 18-Sep-99, to lugnet.robotics.rcx.nqc)
| | | Re: Tasks vs. program slots
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| (...) Dave, It is basically just exactly what you describe. It usually takes about 200us or so to "see" the incoming 38KHz signal, common I suppose for an integrator to react to the signal getting through the band-pass filter, then a Schmidt trigger (...) (25 years ago, 20-Sep-99, to lugnet.robotics.rcx.nqc)
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Message is in Reply To:
| | Re: Tasks vs. program slots
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| Hello Dave, First, let me thank you for NQC ... you've made my RCX playing tremendously more rewarding. I've been wanting to use a Sharp IR receiver to demodulate the signal from a LEGO remote control, and then a PIC to decode the rx output for use (...) (25 years ago, 18-Sep-99, to lugnet.robotics.rcx.nqc)
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