No batteries required
Our daugther has an old toy piano. A few days ago, the batteries started to die and the piano played awful tones that just didn’t sound well. So it was my part to replace it with new batteries or even better get rid of them and add this:
Yes, you’re right, it’s a LJUSA dynamo torch from IKEA and it’s quite cheap. What’s left after breaking it open was this:Attached to the red handle there’s a gearbox combined with a brushless motor (like in your computer hard drive). From there, three black wires lead to the white PCB that has a capacitor (5V, 1000μF), diodes and resistors. The hole thing converts AC current to DC current and stores the energy in the capacitor. The black and white wire are + and - poles.
Well the main part was to attach the gearbox/electronic inside the piano and find a good place for an ergonomic handle operation that suits a two-year-old. I drilled some holes on the back and screwed on tightly the gearbox to the housing. After that I just needed to solder the black/white wire to the corresponding connections found at the now obsolete battery compartment.
After pushing all the wires back inside the housing and tightening the screws, the conversion to a batteryless toy piano is quite subtle, even the handle color is matching with the piano housing.
To be honest: you have to turn the handle for about 30 seconds to play a few tunes. The capacitor isn’t enough powerful to store a lot of energy. But hey, at least it will work forever unless the handle breaks or somebody set it on fire.
I saved for sure some batteries and had some fun moments making it.