Encoder

[dn]

Jim:

>   Why is the wheel going to be a bear. Spot size will allow me to use .2mm 
> marks, the focal points a bit out there but I'll recess the sensor. 

This kind of accuracy requires photo reduction techniques, ya can't just bang
one out on your dot matrix...  Not cheep and not quick...  You'd be much
better off just buying an encoder.  Newark has 100 ppr units that look like 
a pot for around $35, rated for 10,000,000 revolutions.

> But what is the output voltage? And the transition time?

No idea.  The only app circuit I have for this is pretty easy, though.
First, supply the LED (pin 6) via about a 120 ohm resistor to 5v, this will 
give you around 30 mA LED current. (pin 4 is LED ground) 

The detector circuit is dead simple.  Tie the photodiode cathode (pin 3) to 
+5v.  Put in a 100k resistor from pin 1 to +5v, this is RL.  Put a 10 Meg 
feedback resistor from pin 1 to pin 2.  Tie pin 8 to ground.  That's all
there is to it.  Oh yeah, output voltage is also taken from pin 1.  I have 
no idea what the output voltage from this circuit is, just breadboard it up 
and find out.  You may need an extra stage of amplification and a schmitt
trigger to clean it up for your counter logic.  

If you need more info than that, you'll have to contact HP and get some
app notes, I haven't used the thing before, either...

regards
dn


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 Darrell A. Norquay              Internet: dn at dlogtech.cuc.ab.ca     
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