USB Tester on 200mA scaleI am a big fan of the USB tester designed by William at, and I contributed a bit of code a few months ago, to implement scrolling of the USB voltage graph display.

Since the OLED screen on this device is fairly small, I thought it would be nice to implement autoscaling, so that the display always makes the best use of available space. I implemented this yesterday, and it seems to be working pretty well.

Using this updated firmware, the OLED backpack will now change its display scale dynamically from 200mA to 5A. One nice thing if you are a developer, is that you can simply define the scales in one single array at the beginning of the firmware code and you won’t need to touch any other part.

This new feature is already rolled into the official firmware that is available at so go try it, test and report!

One area where I would be interested to get feedback: do you think it is worth displaying the scale on the display? Since we only have 24 vertical pixels, the graph is more of a trend indicator than anything else, so I decided against it. The display flashes a “*” briefly when changing scale, and current reading is always displayed at the bottom anyway…

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