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Author Topic: Arduino Micro that's LiPo compatible  (Read 543 times)
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I am working on a piece of wearable electronics, specifically a wristwatch. It needs the basic functionality of the Arduino micro, but I want to run the Arduino and a couple small motors on a LiPo battery.

The Arduino platform is especially unsuited for LiPo, as it needs over 4.5V to reliably run the CPU at the standard 16 MHz speed. LiPo cells make 4.2V max and 3.3V min. I also would like the USB port to only charge the battery (safely), and for the battery to power the computer rather than the USB port power the computer directly. None of this is possible without a lot of hacking on the Micro board with an Xacto knife.

I may not be the only person in the world with this product requirement.

I have designed a similar circuit for one of my Nixie tube wristwatches. I'd be happy to design this Arduino board, if for no other reason than to make my particular project feasible.

Thoughts?
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16 MHz only needs 3.8V.
Watch doesn't need 16 MHz tho. Use 8 MHz and run from LiPo directly.
MAX1811 to control recharge of the battery.
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I am figuring out the circuitry and prototyping it on a Micro. It's not hard to charge the battery from USB, but it takes some trickery to turn the power to the Arduino on and off as needed. After all, an Arduino is not capable of running for several days continuously on a 150 mAH battery. I'm using an RTC board with its own coin cell to keep track of the time.

I ended up using an LTC4054 chip I had on hand for charging the battery, and one of the two MOSFETs already on the board to switch the Arduino power. I had to build a flip-flop out of a CD4001 to switch the MOSFET on and off under pushbutton control.

I'll post a photo or two when it's working.
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