The LEDs will not work if the voltage is lower than their forward
conducting voltage (Vf).

Your LEDs are likely to have a 2.2 volt Vf (measured by you), and
thuse won't light at 1.5V from a single AA.

You'll need a step up regulator to power them from 1.5V.

-Adam

On Wed, Jun 25, 2008 at 9:43 PM, Tom=E1s =D3 h=C9ilidhe <toe@lavabit.com> w=
rote:
>
> I have bi-colour LED's on my board that have about 2.2 volts across them
> when there's 25 mA flowing through them.
>
> I'm thinking of using a single 1.5 volt AA battery to power my board.
>
> I've got two questions:
>
> 1) Can I go straight from the 1.5 V battery into the LED's without a
> current-limiting resistor?
> 2) What kind of regulator should I use to provide my uC with 5 volts?
>
> Very little current will be drawn from my uC's output pins because all
> the output pins go straight into driver chips, so this can be taken into
> account when choosing a regulator. Something small and cheap to step 1.5
> volts up to 5 volts.
>
> My uC is the 887.
>
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