If you have a Pro Trinket you probably know it's the perfect little
size for a portable project. This LiPoly backpack makes it really easy
to do! Instead of wiring 2 or 3 boards together to make a charging
system, this little PCB sits on top of the Pro Trinket and allows a
LiPoly/LiIon battery to plug in. When the Pro Trinket USB port is
powered, the battery is recharged automatically. Unplug the USB port
and the Pro Trinket will switch over to the rechargeable battery.
Ideally, this backpack is for use with the 3.3V Pro Trinket, so that
the battery voltage (3.7V-4.2V) will get regulated down to 3.3V on the
Pro Trinket board. However, many times, you can run a 5V Pro Trinket +
accessories off of the ~4V from the LiPoly battery with no problem.
(Technically its overclocking but we've never seen that affect the Pro
Trinket itself, AVRs are happy to overclock without complaint).
Solder the backpack on with the extra long header so that it can still
plug into a breadboard, or clip the long header leads short afterwards
for a slim package. There are two LEDs - one red and one green. While
charging, the red LED is lit. When the battery is fully charged and
ready for use, the green LED turns on. Seriously, it could not get
If you want to add an On/Off switch, we also made that really easy.
The two 0.1" holes with a box around them are the battery output line.
Carefully cut the trace between them with a hobby knife and replace
with two wires from a switch like a slide switch, or a pushbutton.
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 bottom, for when
you'll only be charging batteries with 500mAh size or larger.
Comes assembled and tested
* Uses the 5V input via Micro-B USB connector on the Pro Trinket
* For charging single Lithium Ion/Lithium Polymer 3.7/4.2v batteries
(not for older 3.6/4.1v cells)
* 100mA charge current, adjustable to 500mA by soldering a jumper
Batteries and Pro Trinket not included.…more