Just recently, I have found a rechargeable coin cell battery at Sparkfun.com. It provides 3.7 V. at 200mAh. I don't know that my projects will work at 3.7 V. or not. But, I want to give it a try. For portability, I want to charge the battery from my computer's USB port. So, I designed a USB coin cell battery + charger breakout board. Like many simple battery charger, I use MAX 1555 as the controller of the charger.
The schematic:
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi5EpKt2SYGoiYzpZ4Fcm7Vh3Q6txB6CqtaNjZcM1v1uVbcTLiUdkf5d95HQPWPtjWI0W9IWyugZ9S9w_kSgCrmQbijRwYZgfRCrNOSWQHir_H1JAXnGx0oZwxt4iIVCqHaoQbH-AevnxrQ/s400/coin-cell-usb-charger.png)
The single sided PCB (40mm x 30mm):
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjl6qTqERfhxdkjv9zPQznHGiXZtvQYlx4-krNSaiZ_DY1tlCGVvf7oOR3a3D2dUONzwoNkR4XXFbh5uMfvllaNx-Qspi221hrYhEbRYPciSVr0NLSATIYP9Fjpg8y4fF9AY1av98VQvyW9/s400/coin-cell-usb-charger-PCB.png)
The LED goes off when the battery is fully charged (but the charger is still charging).
Please note that the schematic/PCB are just the design and I haven't made it yet. The parts are ordered and I will update when I complete the hardware.