I’ve been thinking more about energy savings with my watch.

I’m already going to be using some kind of Real Time Clock chip so that it only draws a tiny bit of precious power from my battery when in standby, but what about when I power the thing on?

Well, LEDs aren’t current limiting. This means that unless you do something special, they’ll draw a ton of current (and if you supply them with enough current) blow themselves up or at least severely shorten their lifespan. Because of this, you always need to add a current-limiting resistor to protect them.

Here’s how it works: Continue reading →