I bought a couple of cheap wireless optical meeses to have a play with, thinking I might be able to cobble wireless charging (for a lockdown play). Item in question:
My original plan was to hack the wireless charging out of a dead electric toothbrush, but I think the coupling to the coil (in the toothbrush) might rely on that spike from the charger base having a magnetic circuit in it, and the toothbrush circuit only has to charge one NiMH cell - the mouse works from two AAAs.
Then an article in Practical Electronics came along mentioning cheap QI modules (TX and RX), which have 5V in and out, and seems to be a way forward to build into a mouse mat. So I've got stuff on order. Meanwhile, I have obtained some very small LiPos (small enough to fit in the 2xAAA battery compartment... with a little hacking) and have been investigating what is needed to charge them safely from the QI output (a "TP4056 Lithium Charger Module with Battery Protection", plus a P-MOSFET to disconnect the battery from the load when being charged).
It's been doing my nut in working out what the mouse can actually tolerate in terms of supply voltage. Even hooked up to a lab PSU it
would not behave properly, even at 3.0V, and yet with batteries and connected to my PC it worked fine. Ditto No.2. Eventually the penny dropped: the USB receiver dongle is two way! I always imagined they were only receivers - but no, there must be some kind of handshaking. Just powering up the "receiver" in a USB charger is sufficient to fool the mouse that all is well, and it behaves normally again.
While it's hunting for its matching dongle (no, they do not work on each other's dongles), the mouse circuit actually consumes more mA than normally (never more then 20mA, mostly about 6mA and less than 1mA when the LED is off).
The outcome of voltage tolerance? 2-5V - which means I won't need a regulator to run it from the LiPo (via disconnect FET) or 5V (via diode).
Once complete, I will detail the whole build for anyone who wants to have a go. In case you are wondering whether this is worth it (apart from the exploration), look up the cost (and grotesque gamer styling) of a QI-charged optical mouse!