However, in my experiments, these beefy batteries can’t make up for the fact that the little voltage regulator on the Arduino really doesn’t want to deliver more than about 500mA. So I’m investigating alternative ways to get enough juice to the I2C buss.
One good possibility is to set up a completely independent power supply for the hungry I2C buss, then run the Arduino off something more modest, since its power requirements are much lower. So I tried creating a little voltage-regulated power supply for the I2C buss using the batteries and a 7805 regulator. The Arduino Mega, in this setup, just runs off USB power. I bridged the I2C buss SDA/SCL lines over from the Mega. Here’s the setup:
Results? Sigh. The 7805 doesn’t really want to deliver much over half an amp either. So my next attempt will be to create a much beefier power supply, using an LM323 5V/3A regulator.
Before I thought these LEDs drew less current than expected. But now I’m revising that. With the LEDs off, the I2C buss still draws 350mA. That shouldn’t really surprise me – there are 50 little computers out on that buss, spinning in tight loops. So it’s no wonder that turning on the LEDs makes the current go up a lot. I tried filling out a spreadsheet of white-level (1-255) vs current, and with this setup I couldn’t get over white-level 32, at 0.57A.