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Notify me when its in stockInstead of connecting 2 or 3 boards together to create a charging system, this small PCB sits on top of the Pro Trinket or ItsyBitsy and allows you to plug in a LiPoly or LiIon rechargeable battery. When the Pro Trinket or ItsyBitsy USB connection is powered, the battery automatically recharges. Unplug the USB connection, and the microcontroller will run off the rechargeable battery.
Ideally, this Backpack is designed for use with 3.3V Pro Trinkets and ItsyBitsy so that the battery voltage (3.7V-4.2V) is stepped down to 3.3V on the board. However, many times you can comfortably run a 5V microcontroller + accessories off the ~4V from a LiPoly battery. (Technically, it's overclocking, but we've never seen an AVRR run at 16MHz at 4V but underclocking at 8MHz works fine and some AVRs can even overclock to 20MHz without complaint, so 4V is a good place to be, 3.3V may end up resetting the microcontroller).
We also added an optional "load-sharing" mode that will let the Pro Trinket run off USB power but will automatically switch to the rechargeable battery when the USB power is off.
The Backpack is designed so you can solder it in and forget it - but it comes with extra long header so you can use it on a breadboard. Two LEDs let you know when the battery is charging and done.
To make the Pro Trinket or ItsyBitsy a little slimmer, cut off the two mounting ears with diagonal cutters if you want.
The charger circuitry and 1000mAh rechargeable battery are all built in. Itsy nRF52840 note that this Backpack does not cover the reset/user buttons (you can sit it on top and use 3 wires to connect)
Charging is performed in three stages: first a preconditioning charge, then a constant-current fast charge, and finally a constant-voltage trickle charge to keep the battery topped-up. The charge current is 100mA by default, so it will work with any size battery and USB port. If you want you can easily change it over to 500mA mode by soldering closed the jumper on the front, for when you'll only be charging batteries with 500mAh size or larger.
Please note: JST connectors can be a bit loose, especially if the battery is subject to motion or vibration. Check out our lipoly batteries for ones with nice snug connectors.
Please note that for the Itsy nRF52840, this Backpack covers the reset/user buttons (you can sit it on top and use 3 wires to connect)
Please Note: You may get a board with a white or black JST connector. It's normal for the red and green LEDs to be very slightly lit when the battery is connected but not charging, there is 500uA reverse-leakage from the schottkey diode from the charge circuit to the battery.
You can review data sheets, PCB files, and Fritzing on the education page.You can order the Adafruit LiIon/LiPoly Backpack Add-On for Pro Trinket/ItsyBitsy product from the Adafruit category at SAMM Market with competitive prices, same-day shipping, and fast delivery advantage.
