At 09:15 AM 8/24/01 -0500, you wrote:
>
>B. To use a cheap two-or-three transistor amplifier.  I get transistors
>three for a nickel, and resistors four for a penny, so any concievable
>combination of bipolar  transistors and resistors would be plenty cheap.
>FETs (the other obvious choice) are probably out of my price range.  So far,
>I've not been able to get anything to work so well

Maybe you could use two cascaded complimentary BJT emitter followers, say
with 100K & 10K as the emitter resistors. There would be some offset (due
to the difference in Vbe at the different currents),  and the output would
not be able to get closer than one Vbe of the supply rails - but probably not
enough to bother your application (making some assumptions - but
few optos are stable to better than 20% or so. Total cost about a nickel.

Fets.. well there are some for about $0.10, you could use a simple source
follower, but the offset would be more and more variable.

Best regards,
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