My first thoughts were to look for a music sight reading app for my Android phone, which led me to the highly-rated Music Tutor Sight Read Lite. Sleep intervened before I got to test it, during which I pondered whether there was software to somehow connect my Raspberry Pi to my digital piano. After all, the Pi has a great modifiable hardware interface. Then I remembered the existence of MIDI, a way of connecting computers to musical instruments, and checking my digital piano manual discovered that it did indeed provide MIDI over USB. I didn't need the Pi; in theory I could just use a standard Windows laptop. Now I just needed software.
A quick google for free MIDI-enabled sight reading applications led me to the open-source Java software Jalmus. It was quite revelatory the first time I pressed a key on the piano and saw this replicated on the computer screen. Jalmus has a few different modes. The one I played the most was where multiple notes were displayed moving on a grand staff from right to left, and hitting the appropriate keys would eliminate the notes before they hit the edge. The notes appeared at somewhat random order, so the result was quite cacophonous.
Fun though that was, I couldn't help thinking that something like the console game Rock Band would be more fun. You succeed at this game by playing accurately along with famous songs. It displays the keys to hit on the screen, and shows when to hit them. However, it doesn't have sheet music, so it won't help in learning to read music. Anyway, it turns out there is a Rock Band peripheral for connecting to MIDI keyboards, the Rock Band 3 MIDI PRO-Adapter. However, it connects to a MIDI 5-pin DIN port rather than the USB my keyboard has. A gimcrack solution using a PC as an intermediary apparently works, but it began to feel like a lot of effort.
Then I wondered whether there was genuine Windows software which has a Rock Band type game and connects to a keyboard. There is, and it's called Synthesia. The free version is fully functional for a few built-in tunes. Paying for the learning pack lets you use all the provided tunes, and allows you to practice on your own midis. The screen displays the falling notes of Rock Band, and optionally also shows sheet music. It's also a nicely polished product, with pleasant graphical flourishes rewarding any improvements in accuracy or speed.
The final missing piece was that I actually wanted to learn on Synthesia the sheet music I have been practising. Midi files can be found in abundance on the internet, but they are generally created to sound nice when played back, rather than being suitable for learning or playing on the piano. The solution was to create my own midi of my sheet music. Surprisingly there's open-source software which can do exactly that. Well, it doesn't convert scanned scores into midi files, but it does the next best thing, allowing easy manual entry of music to produce printed sheet music and export to a variety of music file formats, including MIDI. This software is MuseScore, and with its great documentation is quite quick to pick up. It took me two hours to learn how to use it and to input my two pages of music. Minutes later I had it ready to go in Synthesia.
Time will tell whether this actually encourages me to keep practising for more than a few months, but early signs are promising. At worst I've had a lot of fun dabbling in the world of music software.