If you use two, you can just switch the DC to each of them to select the
current (you could get a total of 4 current levels, including off, if one
is set to twice the current of the other).

I recently used an LM317 as a current source and needed to turn it on and
off. I put a resistor between the sense pin and the "right side" of the
current sense resistor. Use an open collector to drive the sense pin. With
the collector open, the LM317 current regulates. When the collector is
pulled to ground, the LM317 regulates to 1.25V plus the transistor
saturation voltage. In this case, that was less than the Vf of the LEDs,
so they went off.

Harold

>> To keep the whole thing relatively small and low-cost, the
>> good old generic
>> LM317 comes to mind, but the question is how to set up a
>> single LM317 for
>> dual current levels.
>
> don't, those things are dirt cheap. use two :)
>
> Wouter van Ooijen


-- 
FCC Rules Updated Daily at http://www.hallikainen.com
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist