> > The internal resistor can be replaced by a npn BJT transistor in
> > common-collector
> > setup:
>
> Or you could produce a DAC controlled CC (constant current) driver.
> The following has the advantages of allowing the Arduino etc output V
> to be < 5V (or < 3.3V) and of current driving the LEDs rather than the
> riskier voltage drive method which relies on well behaved LEDs with
> consistentish specs between batches.
>

Should "consistentish" be pronounced with NZ accent? :-) Great posting,
BTW. Sure, constant current driver rules. But, anyway, I'd rather use a
feedback in the form of two photodiodes, one to measure ambient light, and
the second to measure light from the driven LEDs.
--=20
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