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DPRG: biasing & reading a phototransistor

Subject: DPRG: biasing & reading a phototransistor
From: Dennis Draheim dld at cyberramp.net
Date: Wed Aug 18 19:23:38 CDT 1999

David Philip Anderson wrote:
> I purchased and played around with these same sensors from Tanners when
> I was designing the shaft encoders for RR04 (little brother to my current
> robot project) and was never able to get them to behave very consistently.

Ah.  So it may not be just me.  I'll still play with them for a while,
but I may switch over to a different part anyway, since the OPB741's are
a bit bulky.

> I finally settled on a slightly different package from Hamamatsu, the P5587.
> This is a really nice part that includes an infrared emmiter/detector
> pair along with a modulator/demodulator circuit that tends to make the
> sensor very insensitive to ambient room lighting conditions.
> I have used a number of these since in various encoder and measuring
> applications and all have been fairly trivial to make work.  They measure
> about .5cm by .5cm (tiny!) return ~0 volts for detection and ~5 volts for
> non-detection.  This part replaces the older P306201 which you may see
> referenced in various robot texts and designs.

Ah, hah!  No wonder I couldn't find the P306201's anywhere!  These were
the parts I was originally looking for.  I settled for the OPB741's
because they were all I could find locally.

> I just ran a quick net search and found several sources, you might like to
> try one out and see if it fits your needs.  Check out:
>         http://www.zagrosrobotics.com/price.htm
> They advertise $7.00 each, 2 for $10.00.

Thanks!  I'll order some.



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