Arduino Mini Shield for Small Prototypes

Quicker Arduino prototyping with help from a custom shield

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We have developed a small “shield” board for the Arduino Pro Mini that allows us to easily prototype small battery-powered devices that contain motors, lights, speakers or sensors.  This shield adds the following features to the arduino board:

  • Battery charging of a lithium polymer or lithium ion battery
  • Voltage converter of battery voltage to 3.3V.  This will regulate any voltage in the range of 1.8-5.5V to 3.3V.  Without this the things that are powered would get less power as the battery dies (i.e. the lights would dim, motors would run slower)
  • 8 MOSFETs that allow I/O pins to control higher current loads.  The arduino can only source 40mA from a single pin.  This allows a pin to control up to 5A of current.  This is necessary for things like motors or large banks of LEDs


The board can be snapped on top of the arduino board and looks like this when it’s all together:

Here’s how to wire it up:

We are currently talking to Spark Fun to see if we can have these made to be sold to the public.

UPDATE: They started selling a version of this!  It’s missing the battery charger and the jumper that allows you to reroute a button to pin 2 for wakeup from sleep.  However, it’s easy to get and only $20.  Buy it here

We have made the eagle files and bill of materials available if you want to make your own.

Download the source

UPDATE: I had a bit of trouble with the charging speed.  At some points the charger will charge the circuit just enough to turn on the Arduino, then the Arduino will turn on draining the battery.  If you substitute the 1.74k resistor for a 850 ohm resistor, this will be fixed, but you will have to charge with a 5V supply with at least 1A capacity (so USB would no longer work)