Fruit Piano Uses A Different Circuit Than The Makey Makey


[Hasbi Sevinç] is using perishable goods in his electronics project. The orange, tomato, and two apples seen above act as keys for the virtual piano. The concept is the same as the Makey Makey which is often demonstrated as a banana piano. This implementation uses an Arduino to read the sensors and to connect to the computer running the piano program.

You can see there’s a fair amount of circuitry built on the breadboard. Each piece of fruit has its own channel to make it into a touch sensor. The signal produced when your finger contacts the food is amplified by transistors connected in a Darlington pair. That circuit drives the low side of a optoisolator transmitter. The receiving side of it is connected the I/O pin of the Arduino. You can see the schematic as well as a demo clip after the break.

This use of hardware frees up a lot of your microcontroller cycles. That’s because projects like this banana piano use the timers to measure RC decay. [Hasbi’s] setup provides a digital signal that at most only needs to be debounced.


10 thoughts on “Fruit Piano Uses A Different Circuit Than The Makey Makey

  1. I see what he did there: induced noise from contact surface is amplified, then used to trigger the triac (photodiac) part of optoisolator, which then latches and provides smooth DC voltage level on the Arduino input. Arduino resets the diac by changing the input into the output with high level voltage on it, thus cutting off the current which holds diac conducting. Thus the debouncing is achieved.

    However, I wonder if it is cheaper to specify an optoisolator instead of a PNP transistor and a little TO92 housed SCR (e.g. BRX44)? I mean, not that it is much of a hit on the budget, probably a few cents per channel, but MOC3021 perhaps could have been used in some other project for something more fitting, like regulating a heater through phase control.

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