This is a relatively simple modification to any wireless mouse. The basic concept behind this is a solar powered trickle charger. This modification includes a a mouse, a step down voltage regulator, a rechargeable battery, and a flexible solar panel.
Here's what the mod is made of:
Logitech M185 ($15)
1.2 V Rechargeable Battery
Flexible Solar Panels (shown is 3.6V 50 mA solar panel, oddly I don't see it on the website anymore it was $6.95)
Surface Mount Breadboard ($3.50)
30 & 26 gauge wire
4.7 uF & 22 uF Capacitors
4.7 uH Inductor
2 mini packs of Sugru
Step 1: Testing
This isn't exactly a necessary step, but I'm including it anyways, because it helps understand why I choose the values I choose.
I tested two variables here, the size of the solar panel and the type of charging device. So I tested between a larger solar panel and a smaller panel and then also a 70 F super capacitor and a rechargeable battery. I used a TP4000ZC to log the data every 1/4 second and a 40 W bulb to power the solar panel. The base software from that multimeter wasn't that useful so I used a python library to log the data.
These tests revealed that the smaller solar panels I tested at first weren't big enough. They also revealed that the 70 F super capacitor discharged a lot faster than the rechargeable battery. But after implementing the circuit found in the next step and using the largest solar panel I had, I retrieved the following graph above. After about 6 hours of testing with a dummy load of 47 Ohms (simulating the absolute maximum load from the mouse over a longer period of time), the test showed that the solar panel not only sustained a charge, but it also started to trickle charge the battery.
Step 2: Circuitry
The circuitry seems pretty simple, with a down voltage converter. The converter can at most take a voltage of 6 volts and in this configuration the regulator can output 1.5 volts according to this datasheet. This circuit may seem easy at first, but due to the size of the chip, it can take about an hour or so while being careful with regular soldering iron tips and larger gauge solder wire. The circuit was placed on the SMD protoboard and the components were found in my school's electronic supply closet. I'm absolutely sure that the circuit could be smaller, but at the time I didn't get the smaller surface mount components. If this is done the circuitry could easily fit inside the mouse.
Otherwise the circuit was cut down with a bandsaw with a fine toothed blade from another lab. After that the 26 guage wires were used to connect the two terminals from battery casing. This is done taking apart the mouse, soldering the two wires, drilling some holes into the mouse casing and feed the two wires through the casing.
After this the solar panels need to be taken care of. The solar panels come with a plastic sheeting that covers the leads of the positive and negative side of the solar panel, therefore it needs to be peeled back. This can be done with an Exacto knife, where the plastic is basically filleted from the metal leads. The 26 gauge wire then need to be soldered down by applying flux to the leads and then soldering them down. When connecting it to the regulator circuit make sure to check the voltage on the solar panel so that it isn't polarized in the wrong direction.
Step 3: Final Prototype
As you can see from the two photographs the final prototype looks better when the circuitry is hidden. I used two mini packs of Sugru that were also about a year past their due date. Also make sure you follow the directions on the packages carefully, as I should have kneaded the rubber a little bit more before placing on the mouse. I simply used Sugru because a friend of mine had some and so it was readily available, although Sugru could be substituted with any other rubbery type substance that sets. Oddly enough the rubbery casing does provide another resting point for another finger.
I made this in conjunction with several friends of mine that were on a team in an engineering design methods class. While this class was focused on design methods and aspects of project management, I still wanted to make a decent prototype. Throughout this process we analyzed how a mouse could be improved and even found another solar powered mouse in this process.
We originally wanted to put the solar panels on top, but due to the size of the solar panel we decided against that. More solar panels in series or parallel could easily be implemented, along with other step down voltage regulators that won't overcharge the rechargeable battery (maybe 1.2 V instead of 1.5V). Also a final disclaimer, this won't charge under low light conditions. This could be compensated with more solar panels, but as it is right now, the trickle charger does not like dark rooms or rooms with fluorescent lighting. It does however like desks with lamps on them, sunlight, or even (to a degree) having a light filled room with incandescent lighting. Its kind of odd and ironic in that way. Otherwise post any questions or any clarifications.