Subject:
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Re: IR transmission
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 8 Aug 1996 13:56:20 GMT
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Original-From:
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David Negro <negro@ICD.Teradyne+saynotospam+.COM>
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Viewed:
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2376 times
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Jeff,
You are right. Several things could be wrong here. First of all the precision
resistor is VERY VERY important. This controls the frequency of the carrier
signal. The freq is approx 1/(RC) where R = R4 and C = C6 of the the Handyboard
IR Tx circuit. So with handyboard values, 1/(3.83k * 0.0068u) = 38.4kHz If
you chose say a 4K resistor, this would be, 1/(4k * 0.0068u) = 36.8kHz plus any
discrepancy due to the resistors 5% precision. This is probably too far away
from the 40kHz desired.
Secondly, I wrote the REC receive in such a way that it would accept and decode
2 different types of code. But the transmit code will only send one type of
code. What do I mean?? If the Rx program sees a $4703 for a code (BTW the $47
part should remain the same for all buttons on that device, eg VCR) then the
actual transmission could have been one 2 possibilities. It could either be
$47B803FC or $4703. Notice that $B8 = !$47 and $FC = !$03. Thus to make life
easier and the Rx program more broad, I allowed it to accept either version.
The Tx program sends the longer one, however, because well... this is the
version that my remote sent.
Could I make another version of the Tx program to do the shorter code? Quite
easily. When can I get to it? Well my monitor went on the fritz last night
and isn't accepting my video signal anymore. And I am almost done with some
routines (non IC) to do PIC16c84 programming. Once I get that done I could
make another Tx routine.
Also I have somewhere a routine to compute the frequency of a digital signal
using the pulse accumulators. I suppose this could be used to determine the
frequency of the carrier signal.
Hope this helps,
-Dave Negro
dln2@cornell.edu
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Message has 1 Reply:
 | | Re: IR transmission
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| (...) Well actually, even though it's not a precision resistor, when I installed it, I grabbed a bunch of resistors and measured each one with my DMM until I found one which was between the 3.74 and 3.83 values Fred specified. To further test this, (...) (28 years ago, 8-Aug-96, to lugnet.robotics.handyboard)
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