Logitech K750 wireless solar keyboard mod

I've had a few Logitech K750s now and while they usually work great for about 2-3 months, they're notoriously bad for recharging and keeping a charge. Tired of dealing with this obvious flaw, I decided to "upgrade" mine to be a USB-charged battery-powered keyboard with a heftier battery.

Peeling off the glued front cover. (I salvaged my solar panels for another project since I wasn't going to need them)

Removing all the screws and popping the clips reveal the insides of the K750,
an Atmel ATXMEGA32D4-AU and a Nordic NRF24L01. 

On the reverse side of the PCB Logitech was nice enough to break out power & SPI to pads for us.

Without any disassembling, the original battery holder is removable with a little bit of prying and wiggling.

Taking some measurements with calipers and a little time in SketchUp, I recreated the battery insert with channels for some stripped solid core 22AWG wire to slide through. This provided a nice contact to the battery terminals inside without requiring any disassembly and a case for our new battery. Out with the old 65mAh coin-cell, in with the new 1000mAh LiPo (that should last a little longer and I had one laying around already...)

The 90 degree block was made as a separate piece due to too much friction while inserting the wire.

The first prototype, printed @ 230C/105C HBP. 0.2mm 50 travel/80 feed, 2 shells.

The original ML2032 is a 3v whereas our new LiPo is 3.7v. This shouldn't be a problem since the old solar cells output 4v to charge the coin-cell on the same circuit, so the regulator should be able to handle 4.2v. Testing a few points around the board, it appeared everything was powered by the regulated 2v "V_MAIN".

Plugged in and functional.

There's plenty of room for improvement but it serves it's purpose for now. It could use a bit of work in the aesthetics department and I originally planned on adding a LiPo charger with a microusb connector but it's been 3 months now and the battery voltage has only dropped ~0.05v, I'm probably not going to be needing it anytime soon... Maybe 1000mAh was a little overkill.


Like any wireless keyboard, "secure" or not, encryption on these devices are a joke. But I'm sure I'm not the only one who sits at their PC in a Faraday cage right?

Treasure chest

Printer settings: 10% infill, 1 shell, 0.27mm layer height, 230c / 110c HBP

Scaled down to 66% of the original.

Brown acrylic paint on the rough texture gave an excellent wood grain look

You can see the bottom edges have a bit of a curl upwards, 110C is a little too hot for my HBP. 105C seems to produce much better results.

Hinges snap together.

Map painted with watercolors.

3d printer test + cat = dunce cap

Testing out dual extrusion on the FlashForge.

Kitty was not amused

While dual extruding did work just fine there were a few issues. There is a slight offset on the X axis but only ~0.05mm this could just be that the heads on not sitting perfect on the carriage. Also during dual extruding both nozzles are always kept at 230C this causes the nozzle not in use to slowly leak ABS all over the print. Too bad the firmware doesn't keep the nozzle just under melting temp until needed.