All of the hard work was done in this project. The concept of the 1-T amplifier is explained here. And then I did a little work to create a children's organ / synth from it.
It has two voices, and aims to be parent-friendly (= not too loud). A video of the toy in action can be found here.
The original project has a fancy amplifier/filter end stage. You can build that for proper sound. However, I wanted to try if I could build something with minimal components that I already had. A PC speaker seems to work well. The inertia of the speaker does some poor man's filtering. The transistor can be a regular NPN, for example a BC550.
All the buttons are connected to the Dnn-ports and ground. You can choose to connect the speaker to 5V instead of 3V3 for louder sound.
Disclaimer: the speaker may run a bit out of specifications. Don't blame me if it blows up...
After my changes, it doesn't win the beauty or clean code prize. However, it does work. With the 1-T amplifier, only the square and triangle waves sounded well; I couldn't get the sine to work. For this you probably need to build a proper amplifier/filter stage. The first voice has a regular scale (CDEFGABC), the second voice is pentatonic (CDEGACDE if I remember correctly), fitting well with a guitarish sound.
This work (as was the original) is licensed under the Creative Commons Attribution-ShareAlike 4.0 International License. To view a copy of this license, visit https://creativecommons.org/licenses/by-sa/4.0/deed.en