Though everything looked good, when I switched to battery power, it stopped working. The test program I’m using lights one LED at a time, switching every 100 ms. So, I can tell that the board runs for between 100ms and 1 second before it just dies. This is similar but much worse than my very first design using batteries that couldn’t supply enough current. However, I’ve used this design with AAA batteries before. I’ve looked at the AAA datasheets and they should be well within spec for this.

But maybe the LED driver is pulling way more current than I thought and dropping the voltage to trip the brownout? I checked with my new bench power supply and I see I can run it down to 2.7 V, so that’s not a problem. At that voltage, it’s only drawing 7 mA of current, so I can’t be pulling too much from the batteries.

Just to be sure, I hooked up a scope and see things like this:

Sure enough–after around 200 ms, the power just drops! It wiggles around for a few hundred ms. What can be causing this? There’s no problem with a real power supply… Is it something funky due to the modifications I had to make with the dremel? What is going on?