Subject:
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Re: 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 01:32:44 GMT
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Original-From:
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Chuck McManis <CMCMANIS@FREEGATEstopspammers.NET>
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Reply-To:
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cmcmanis@(stopspam)freegate.net
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Viewed:
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1443 times
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Adam wrote:
> 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.
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 in your
output circuit such that the voltage level of the A/D input pin
is interfereing with your amplifier) HOWEVER, a simple way to
rectify this (read a hack) is to use an op-amp in a voltage
follower mode (connect your signal to the '+' input, connect
the output of the op-amp to the A/D input and back to itself
on the minus input. The output of the op amp will follow the
input from your circuit and your circuit will believe its
connected to air (op amps have a very high input impedence)
Use an Opamp that works well on a single supply like a 301 or
something (_don't use a 741_)
--Chuck
--
cmcmanis@netcom.com http://www.professionals.com/~cmcmanis
All opinions in the non-included text above are the sole opinions of
the author.
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Message has 1 Reply:
 | | Re: analog header
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| Certainly the voltage follower will work. But I had a similar problem adjusting the sensitvity of a photocell that I solved by paralleling a pullup resistor of my own to get the proper impedance. You might try putting a 1 ohm (yep, thats one NOT 1k) (...) (27 years ago, 5-Apr-97, to lugnet.robotics.handyboard)
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Message is in Reply To:
| | analog header
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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 (...) (27 years ago, 5-Apr-97, to lugnet.robotics.handyboard)
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