Don't toss the pumpkin: turn Halloween leftovers into a touch piano

Halloween is over, and there's probably a pumpkin or two sitting by your door. Before it goes in the compost, your kid can turn it into an instrument. With a few pieces of fruit, a cheap touch kit and some code blocks, you can build a piano you play by tapping pumpkins, apples and bananas. It takes about 30 minutes, and it shows something real about how every button, keyboard and game controller works.

Why are makers building squishy, fruity controllers?

Makers are building them because any touch, squeeze or tap can be an input a computer reads. Two projects in Make: magazine this week show the idea:

• A banana-shaped synthesizer. On October 27, Make: reviewed the Banan-a-Synth, an $80 touch keyboard shaped like a banana. It has 20 touch pads instead of piano keys and can sound like different instruments. It also comes with alligator-clip wires so you can make instruments out of anything that conducts electricity, like real bananas. The reviewer, a teacher, liked that it's screen-free and the keys fit small hands.
• A squeezable cow controller. On October 29, Make: published Karina Chow's Udderly Fantastic Game Controller, a soft silicone cow udder you squeeze to the beat in a rhythm game. Inside each part is a sensor that notices how hard it's being squeezed. A small computer board turns every squeeze into a key press.

The fruit piano works on the same idea, and it's much easier to build.

How does touching a pumpkin make a sound?

Your body and the fruit can both carry a tiny bit of electricity. Fruit and pumpkins are full of water with a little salt and other minerals in it, so electricity can travel through them. A touch kit like a Makey Makey plugs into a computer by USB and pretends to be a keyboard. You hold one wire, called "Earth" or ground, and clip another wire to a pumpkin. When you touch the pumpkin, you close a loop through your body, and the kit tells the computer a key was pressed. The computer doesn't know it was a pumpkin. It just hears "space bar."

The current is very small and completely safe to touch. It's the same kind of power that comes from a USB port.

What do you need?

• A touch kit that works with alligator clips. A Makey Makey is the classic one for kids. The Banan-a-Synth also has clip wires and needs no computer.
• Alligator-clip wires (most kits include them)
• Four to eight things to play: small pumpkins, gourds, apples, bananas, oranges or even a bowl of water
• A laptop with Scratch or any block coding tool open in the browser
• Paper and pencil to plan the instrument

A note on pumpkins: a carved jack-o'-lantern spoils fast. If yours has gone soft or moldy, compost it and use uncarved pumpkins, gourds or fresh fruit instead.

How do you build it?

1. Draw your instrument first. Ask your kid to sketch the layout: which fruit plays which note, high notes on one side and low on the other. Is it a piano, a drum kit or a sound-effects board? The drawing is the design.

2. Wire it up. Plug the kit into the computer. Clip one wire from each key on the kit (arrow keys, space, click) to a different piece of fruit. Clip one more wire to Earth, and have the player hold its metal end, or wear it around a finger.

3. Code a note for each fruit. In Scratch, add the Music extension. For each fruit, make a script: "when [up arrow] key pressed" then "play note 60 for 0.25 beats." Give each fruit a different note. Kubrio's free coding guides cover blocks like these if your kid is new to them.

4. Test and tune. Tap each fruit. If one doesn't work, check the clip and make sure the player is still holding Earth. Swap notes until the instrument sounds right.

5. Play a song. Try "Twinkle, Twinkle" or make up a spooky tune. Record it.

How can kids level it up?

• Make it a drum kit. Change the notes to drum sounds.
• Make it a game controller. Use the same pumpkins as arrow keys to steer a character in a Scratch game. Now it's a controller like the cow udder, only orange.
• Add a person. Two players can each hold a hand, and a high five becomes a key press. Kids love this one.
• Test what else works. Try a spoon, a leaf, a pencil drawing (pencil graphite conducts), a cup of water and a plastic toy. Which ones play a note and which don't? That's a real experiment in which materials conduct electricity.

Where does Kubrio fit?

Kubrio is a set of studios where kids 6–13 make real things, and every project starts the way this one does: your kid draws the idea first, then builds it. If your kid's fruit controller sparks a game idea, Kubrio's Game Studio is where they can draw the characters and build the levels, then share the game with the family from a link. The rule across every studio is the hand stays the hero: the tools help, and your kid makes the choices.

What to do at home this week

1. Gather four pumpkins, gourds or pieces of fruit before they hit the compost.
2. Have your kid draw the instrument and pick a note for each one.
3. Wire it up and code one note per fruit.
4. Record a 10-second song.
5. Test five other household objects and sort them into "plays" and "doesn't play."
6. Compost the fruit afterward and keep the kit for the next build.

FAQ

Is a fruit piano safe for kids? Yes. Touch kits like Makey Makey run on the low power from a USB port, and the current that passes through your hand is tiny. Wash hands after handling old pumpkins, and skip any fruit that's moldy.

Why does fruit conduct electricity? Fruit is mostly water with dissolved salts and minerals, which let a small electric current pass through. Dry things like plastic and wood mostly don't, which is why they won't play a note.

What age is this project good for? Kids 6 and up can wire fruit and play with help. Kids around 8 and older can usually code the notes in Scratch on their own and turn the piano into a game controller.

Do I need a Makey Makey? You need some kind of touch kit with clip wires. A Makey Makey connects to a computer so kids can code it. A self-contained instrument like the Banan-a-Synth plays sounds without a computer, but it can't be reprogrammed.

What else can kids turn into a controller? Almost anything that conducts: a bowl of water, aluminum foil, a pencil drawing, metal spoons or a friend's hand. Kids can design a whole controller from foil shapes on cardboard.