I added Wireless Charging to my A4 E-Reader

Some Motivation

I have a Fujitsu Quaderno A4 (Gen.2) e-reader that I’ve been using for a few years now. It’s light and thin enough that it feels like ten sheets of cardstock and has a paper-like textured screen. There’s also an open-source library which can sync a local directory with it (Thanks to everyone who worked on it!). I take notes¹, reading papers and books, and to quickly sketch designs with it, and it mostly works great (ignoring the closed-source firmware).

However, it’s not without downsides. I usually use up the battery in a few days. That is, not a constant number of days but sometimes 3, often 4, and rarely 7. Having to unlock it and see how much charge it’s at or having to charge it every night is cumbersome not counting the following reason. More importantly, the device’s build quality is not great. It’s bendy and a thin plastic piece around the USB-C port broke off.

Disassembly

Opening the Quaderno up seems quite scary (given how frail it feels), but it’s actually quite easy to losslessly disassemble. Slide in a couple credit cards (three to be safe) in the bottom corners (and middle). Then, making sure that the entire bottom few centimetres of the plastic are out of the way, smear the display down and off the plastic cover. After a few centimetres more, the two halves should come apart.

The electronics are all on the display side.

Adding the Receiver Coil

I got a set of Qi receiver coils with a PCB that outputs DC 5V. I sacrificed a USB-A to USB-C cable, and took the power lines and soldered it to the coils’.

Initially, I placed the coils on the battery. However, it didn’t charge well (i.e., even with the coil as close as it could be). Also…turns out the battery was the thickest part of the internals, and the case didn’t close…good thing I didn’t force the case closed!

I found a better spot, above the battery, and it fortunately didn’t conflict with the plastic fins (or the plastic cover, probably for structural integrity). I realized while writing that putting the coil against the diecast is not optimal. While testing the setup, I found it gets quite hot and it stops charging (!) after half an hour or so—presumably due do some thermal cutoff. Instead, I put the coil against the plastic case so that it’s close as possible to the charging coil, hopefully reducing thermal loss.

Now, time to close the cover (for real this time)!

Charging Performance

I left it on the charger overnight and jotted down the battery percentage whenever I happened to glance at it. Charging is fairly linear, at roughly 13 percentage points an hour, and it topped out at 100% a bit under four hours after starting at 51%.

I’ll spend a few months with this setup, and write another post on how it’s like using it. Be sure to subscribe to the Atom feed so you don’t miss it! (*´∀｀)ﾉ  ♪