Experiments in wearable electronic art.

Scotty! We need more power!

Leave a comment

Current Test

Current-testing the full MiniMe harness

My plan, power wise, was to get four of these LiPoly batteries in series-parallel and feed 7.2 (or more) volts into the VIN pin of the Arduino, then pull I2C buss power off the Arduino’s 5V regulated rail. I needed to do this because the MinM LEDs run at 3.8V to 5V max.

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:

Current Setup

Current test 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.

Author: regenesis

Seattle New Media artist.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s