MintyCharger “9V” Battery Charger
This USB-powered board fits inside an Altoids tin, recharges different types of 9V-style PP3 batteries.
While most common batteries come in a familiar cylindrical format, 9V batteries instead come in a rectangular cuboid shape. This style was conceived of by Ever Ready as the Power Pack 3, or PP3, in the 1950s, and has stuck with us since then. Today, we can get rechargeable “9V” batteries, but as outlined in this MintyCharger product listing by Innove Workshop, not every PP3 format device is the same.
In fact, battery voltages can vary from 7.2V to 9.6V, and most chargers just provide a fixed voltage and current limit. The MintyCharger, however is set up to accommodate different battery types in this format, whether the very common NiMH at 9.6V, 8.4V, or 7.2V or the newer LiIon at 7.4V. A Microchip PIC16F18235 microcontroller is the brains of the board and it’s also capable of discharging batteries, and doing a discharge/charge cycle to restore the battery’s health.
The MintyCharger takes the form of a PCB shaped so that it fits inside of an Altoids tin, thus its “Minty” moniker. You can even order the tin component for it as well, though you’ll probably save a few bucks buying one at the grocery store. Cleverly, the tin supports the bottom of the battery when charging, holding it securely against the positive and negative connections. Power supply is via a common micro-USB cable.
More info is available on GitHub, as well as the Innove website. The system is released under an open source license, and has ICSP pins broken out, so perhaps this could even morph into and/or inspire something new!