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[DPRG] Using an IR LED as IR photodiode
Subject: [DPRG] Using an IR LED as IR photodiode
From: DeltaGraph at aol.com
DeltaGraph at aol.com
Date: Tue Oct 24 11:42:07 CDT 2006
As for your 150 RPM micro mouse / line follower needing fast response.
I would tend to say the quicker response the better.
If your encoders are mounted to your wheels -- say 16 counts per rev -- then
you are probably OK on response time. I was seeing a rise and fall time of
about 5 ms on my scope.
If you lose encoder counts, that is easy to diagnose, but lag in line
detection might be a bit more tricky.
Except for slow rise and fall time, I was pretty happy with results of LED
sensor and a 1M feedback resistor connected to op amp last evening (running
sensor in photoconductive mode).
>If you noticed carefully, the formula I typed in the picture is a
>little bit inverted...
Formula looked OK to me, written another way Gain = 1+(R2/R1) -- makes it
easy to see that the gain will always be at least 1 for this (non-inverting
amplifier) configuration.
I found understanding how resistor dividers work through simple application
of Ohm's law to be very helpful before taking on understanding op amps.
Certainly there are some very nice explanations of all of this on the internet...
-Ron
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