Subject:
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analog header
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 5 Apr 1997 00:36:54 GMT
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Original-From:
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Adam <adam@ring.zenox.NOSPAMcom>
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Viewed:
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1442 times
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I am currently trying to put together an IR collision
avoidance system.....
I'm using the HOA2498-002 IR diode/transistor package which
is hooked up to a darlington pair (increased sensitivity)
Using a digital output to turn on the diode via a 2N4124
NPN transistor, I basically taking a reading for noise
(IR diode OFF) then a reading for measurement (IR diode ON
- noise included) Then take the diff. giving me a fairly
noise free measurement.
PROBLEM:
When measuring the voltages from the receiver circuitry,
I get good sensitivity and response from the pickup on the
IR transistor. BUT when I hook this up to the HB the
sensitivity is lost because I then have to deal with a 47K
pullup on the analog ports. In balancing the 47K pullup
with a 20K pulldown so as to get a reading at all (other
than the 5V pullup) I lose the sensitivity of the sensor
circuitry. This is extremely enoying. Before I rip that
damn 47K pullup out, I was curious if anyone has any alternate
suggestions as to how I might keep from modifing the HB and
have sensitivity of my circuitry.
You see, I can see the voltage that I wish to feed my HB's
analog port, but the 47K pullup destroys it. The pulldown
required to get any reading at all destroys the sensitivity
of the sensor circuit.
Oh well, any suggestions would be greatly appreciated.
Thanks.
----------------------------------------------------------
Adam B. Cox check out my web page
Computer Engineer http://www.zenox.com/~adam
Zenox Communications Corp. vmail: 416-241-7000 (x224)
----------------------------------------------------------
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Message has 1 Reply:
 | | Re: analog header
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| (...) This is known as an 'impedence mismatch'. Basically your NPN amplifier is incapable of driving the analog input low (which in itself seems a bit weird since you only need to sink .1 mA to do that which suggests that perhaps there is feedback (...) (27 years ago, 5-Apr-97, to lugnet.robotics.handyboard)
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