How to turn kids' old piano toy to a MIDI keyboard¶

Inspired by http://www.codetinkerhack.com/2012/11/how-to-turn-piano-toy-into-midi.html I did the same with a Blue Pill module using Mbed.

The old toy was capable to play only one tone at a time:
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A bit of reverse-engineering was needed to re-use the original printed boards. The results are below.

Original PCBs with switches traced to the connector pins:

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Schematic:

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Wiring:

Then I replaced the original chip with a Blue Pill module and added a USB connector:
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Works great when connected over an USB cable to a Linux Ubuntu 18.04 machine¶

Installed software:

• Yoshimi: An excellent MIDI software synthesizer for Linux.
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• Patchage: Provides a graphical interface to connect jack and midi inputs and outputs.
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How to use it:

• Connect the Keyboard to the PC over an USB cable.
• Run Yoshimi.
• Run Patchage and connect the Mbed USB Audio MIDI 1 output to Yoshimi's input (drag Mbed Audio MIDI 1 over yoshimi input and drop)

• To apply the changes close the Patchage!
• On Yoshimi's toolbar click on Instruments and select Show Stored ...
• Select a bank and click on the instrument you'd like to play.
  

Have fun :-)