Sunday, August 9, 2015

VA Tester and our Giant Star

Once upon a time on a bright and sunny afternoon, I decided to interact with some photons from that big burst of energy we revolve around. I had ordered a 6V 3.5W solar panel from Amazon awhile back but I never got around to trying it. I also had an Adafruit Solar LiPo Charger that I hadn't used.  Part of this is research of using solar with home automation nodes that are near a window. Currently, I use AA batteries but I see them as wasteful since eventually you have to replace them. Of course you can get rechargeable AA batteries but they usually put out a tad less voltage, 1.2V vs 1.5V and still uses energy from an outlet to recharge. ( could recharge them from solar?) This setup using off the shelf parts is a bit more pricey but in theory could last indefinitely on the same set of batteries. The Adafruit charger is where the magic happens. It takes care of load sharing with a 1S LiPo battery when there isn't enough Sun and it will charge when there is enough Sun. Ideally in the end, I would design a node that incorporates this circuit but it's really only needed for window nodes.  I could create two types of nodes - one for solar and one without, or an easy add-on board to solar enable a node, hmm...

I set up measurement in two ways. First the above, where the VA Tester is inline with the load and then inline with the battery. This is where I realized a use for the ability of the INA219B sensor to measure negative current. I can now see when the solar charger is draining or charging the battery and at what rate. Pretty cool, eh?

I used an Arduino Leonardo as a load with a blink sketch and as a 5V regulator for the backpack. I also modified the blink sketch to blink rapidly ten times on boot so I could tell if power was being interrupted.

I wanted to see how the charging rate changes throughout the day without sitting there watching or having my laptop connected for logging. So this was a perfect opportunity to put the USB Tester Bluetooth backpack to use.

Here are some screenshots of monitoring the battery load throughout the afternoon. A few times I had to move the panel so that it wasn't getting shade on the corner, as evident in one of the screenshots.

Finally the last screenshot I modified the USB Tester app to handle negative current. This will need some work before I add it to the released version. May need a firmware tweak as well since the min current after going negative is always 0.00V which doesn't seem right to me.

I am happen with the outcome of this test and definitely will expand upon it. Time for some EagleCAD work!


  1. Where can I buy the parts for this

    1. Hi, the USB Tester and VA Tester can be found at


    2. Forgot to mention the Bluetooth Edition isn't released yet but the app will still work with a USB OTG cable. Or you can use a desktop computer.