Fruit piano uses a different circuit than the Makey Makey

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[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.

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Toorcamp: Banana Piano

Banana Piano

[Michael] built his own clone of the popular MaKey MaKey Kickstarter project. His implementation uses an ATMega328 and the V-USB stack to connect as a USB Human Interface Device. He was showing it off at Toorcamp wired up to a banana piano, which captured the interest of kids and adults alike.

The digital inputs are pulled to ground with a large (10 Mohm) resistance. The user holds a supply voltage in one hand and completes the circuit by touching a conductive object like a banana, which is connected to a digital input of the ATMega328. Since the internal resistance across your body is typically around 1 Mohm, this pulls the input high and corresponds to a key being pressed on a normal keyboard.

We featured banana pianos before, and it’s a great demo of the interfaces that can be built with this project. This implementation is very simple, and works well if your internal resistance is low enough. [Michael] taught a workshop at Toorcamp to show people how to build their own. He has found that the ‘magic’ of playing music with bananas is a great way to get children interested in electronics.

Bananaphone lets you use fruit and other things as switches

We’re used to [Sprite_TM] rolling out his own hacks hot on the heels of new concepts. Now we’re glad to see that [Jeff Ledger] is doing the same thing here. He was inspired by a Kickstarter project which vows to let you use fruit, clay, and a number of other common (but weird for this use) substances to interface with electronic projects. The mess you see above is the Bananaphone, a synthesizer played with touch sensitive bananas. Think of them as keys on a piano.

The interface works by measuring R/C decay. Each banana is connected to its own input pin on the Propeller board. The capacitance of the bananas rise when you touch them, and this results in a longer R/C decay measurement. Calibrate the target decay period, and you’ve got a reliable capacitive touch sensor which also happens to be delicious. Check out the results which [Jeff] achieves in the video after the break.

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