SquidBee has been created to be capable of behaving in an autonomous way, which means that it needs to be supplied independently of the main power. As long as many of the sensor networks are going to be implemented outdoors, a solar cell is the best way to keep a mote powered, charging permanently its battery so the only maintenance needed at this respect would be to change the battery at the end of its life. According to this thought, we have created a solar power module for Arduino.

The board we have designed is based on a charger for Li-ion batteries and a DC-DC conversor to supply the 5V. the SquidBee mote needs, and includes three different inputs: a couple of pin connectors (VCC and GND) for more than 6V. cells, another couple of pin connectors for up to 6V. cells and a mini USB connector. The two last connections go directly to the battery charger, but the first one goes through a TS1117BCP50 regulator whose output is limited to prevent the charger from any damage caused by a too high voltage. The mini USB connector has been added in order to allow the battery of the mote to be charged when it is not possible neither to attach a solar cell nor to connect it to the main power.

We have selected a MAX1555 charger from Maxim to energize the battery. This module can handle two different inputs, one that bares voltages from 3.7V. to 7.0V. that will be used to charge the battery from a DC source and another one that bares voltages from 3.7V. to 6.0V., used to carry out the charge from the USB. The MAX1555 output to the battery provides a typical charging current of 280mA and a voltage of about 4.2V, though it may change depending on the battery and its state.
A MAX1674 converts the 3.7V. that we approximately have in the output of the battery into the 5V. the SquidBee mote needs to work. This device bares an output current up to 300mA, which should be more than enough to supply the mote whatever the sensors you have added.
We have also placed some capacitors of 100nF and 47uF in the inputs and in the output to the SquidBee in order to prevent noise from entering the circuit through the supply source.

Finally, the SquidBee mote with the solar module has been tested in two different ways: first, we have tryed to charge a completely empty battery disconected from the SquidBee utilizing each of the three inputs, and afterwards we tryed to supply the mote with it to check that it was fully charged. Secondly, once we have confirmed it works properly individually, we have tryed out the whole system, connecting the battery to the mote and to the supply source (solar cell or USB) through the board at the same time; proving that the mote behaves well all the time.

In this image we can see where each device must be connected to the board to work properly.