gemma M0 power Moderators: adafruit_support_bill, adafruit

[Russ_H]

I have been making a wearable device to flash a 40 hz light directly into the eyes for friends and family who have someone dealing with Alzheimer's, dementia and in one case cognitive difficulties from a stroke. I am using a Gemma M0 to control 2 bright white Leds powered by the 2x 2032 coin cell battery holder with a JST connector soldered on. The coin cells power it just fine but I would like to look into replacing it with a rechargeable LiPo battery. I am unsure how to wire a LiPo battery and charge controller to the Gemma M0. The coin cell holder is pretty simple, but the batteries need to be replaced after about 13 hrs of runtime and I could easily double that with a Lipo battery. As I understand it, the Gemma M0 cannot be used as a charge controller for the battery and a separate one would need to be added. Can I put a charge controller such as the https://www.adafruit.com/product/1904 in parallel with the Gemma and battery such as https://www.adafruit.com/product/1578 without causing any issues?

[dastels]

You'll want a LiPo Backpack: https://www.adafruit.com/product/2124.

I've done just what you have in mind, but with a CircuitPlayground.

The battery plugs into the battery connector, the BAT and G pins connect to a 2-pin JST cable just like the one on the battery https://www.adafruit.com/product/261 which plugs into the battery connector on the Gemma, and the 5v and G pins connect to 5v & ground of a USB connector: https://www.adafruit.com/product/1833 or https://www.adafruit.com/product/1764. The backpack stays connected to the battery and Gemma. Plug in a USB cable to charge the battery (and power the Gemma while doing so). You can wire an on/off switch to the backpack as well if desired.

Note that the USB connector will just power the changer, not let you program the Gemma; you still need to use the Gemma's USB connector for that.

Dave

[Russ_H]

Thank you, I have the parts on order now. One interesting thing to share with anyone else building a project similar to this is that there is a speed difference when the Gemma M0 is connected to USB for programming vs being connected to a battery pack. It's small, but it is there. When I am connected to USB I have to tweak my programming to get 41.11 Hz in order to have a 40.00 Hz output when connected to a battery. I'm interested in finding out if this is true for the LiPo batteries.