AVR-Chat

At 09:23 PM 3/10/2004 +0000, William Nachefski wrote:
>Wow!  what a response.  Actually my tolerances are quite large, + or -
>  say 10 m/sec.  As for placement of the sensors I have no set length
>yet, I just threw 1" as an arbitrary number.  What distance would be
>best?  I do intend to condition the signal of the sensors before the
>uC.  As for accurate distance between them I was going to use a dial
>caliper.  Is that accurate enough, obviously the larger the distance
>apart the less important it becomes.  I think I will go with 10
>centimeters apart.

Your error will be mostly in the response time of the two phototransistors, 
and in the problem of determining exactly when the beam is to be called 
"blocked".
10% drop in light, or 90%, and what is the gain of this phototransistor 
today, at this temperature, anyway?

A photodiode, amplified by a current to voltage converter, is more 
repeatable.  Don't let that scare you, a current to voltage converter is 
just a simple op-amp circuit. Of course the op-amp you use also has to be 
fast enough to play this game..

A tip: Make the IR light sources LOUD, and make the optosensors relatively 
deaf.