1. Repository
2. Overview
For this assignment, I built a hands-free switch that uses the human body as a conductor. The project uses two aluminum foil patches — one taped to the floor, one to the sole of a shoe — to open and close a circuit through the act of jumping. An Arduino reads the state of the switch using digitalRead and communicates over USB serial to a Python script running on a laptop, which plays and stops a song based on the jumping rhythm. The music only plays while jumps are happening in close sequence, stopping if the user pauses for more than 1.5 seconds.
3. Concept
My goal was to turn the whole body into an instrument of interaction, removing the hands entirely and replacing them with something more physical and committed. The initial inspiration came from an unexpected source: my baby nephew, who kept interrupting my work sessions. Rather than fighting the disruption, I decided to include him in the project. Babies and toddlers are defined by their movement — bouncing, jumping, stomping — so building a switch that is activated by jumping felt like a natural way to design around him and his abnormal enthusiasm for dancing. The idea became about handing control to someone who couldn’t operate a traditional switch at all.
The music-as-reward mechanic adds another layer that felt personally fitting: the music only survives as long as the jumping continues, stopping if the user pauses for more than 1.5 seconds. For a restless toddler this creates an instinctive feedback loop between movement and sound. Stop jumping and the music dies. Keep going and it lives.
4. Process and Methods
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- I began with the physical circuit, using the INPUT_PULLUP mode on Pin 2 to avoid needing an external resistor. This keeps the pin held HIGH when the circuit is open, and pulls it LOW when the foil patches make contact through the body.
- To filter out noise and false triggers — particularly the pin floating when only one foil patch was touched — I implemented a two-stage debounce. The code waits 50ms after detecting a change, then re-reads the pin to confirm the state change was real before acting on it.
- On the software side, I wrote a Python script that listens on the serial port for LANDED and JUMP messages. Rather than toggling the music on a single event, I used a timeout system: every landing resets a timer, and the music stops only when that timer expires without a new landing.
- The serial communication bridge between the Arduino and the laptop uses the pyserial library, and audio playback uses Mac’s built-in afplay command via Python’s subprocess module, keeping dependencies minimal.
5. Technical Details
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- The core of the switch detection relies on INPUT_PULLUP, which activates an internal ~50kΩ resistor inside the Arduino chip. This pulls Pin 2 to 5V (HIGH) by default. When the foil patches make contact, they create a conductive path through the human body to GND, pulling the pin LOW.
pinMode(jumpPin, INPUT_PULLUP);
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- The debounce reads the pin twice, separated by a 50ms delay, to confirm that a state change is genuine and not electrical noise or foil flutter on contact:
// Only act if the state has changed since the last loop
if (currentSwitchState != lastSwitchState) {
// Wait 50ms before reading again — debouncing — one landing could trigger dozens of false readings.
delay(50);
currentSwitchState = digitalRead(jumpPin);
// Re-check that the state still differs after the debounce delay.
// If the reading went back to the original state, it was just noise — ignore it.
if (currentSwitchState != lastSwitchState) {
if (currentSwitchState == LOW) {
// Foil patches are touching — the circuit is complete — user has landed
digitalWrite(ledPin, HIGH); // turn LED on as visual confirmation
Serial.println("LANDED"); // notify the Python script to start music
} else {
// Foil patches are separated — the circuit is open — user is in the air
digitalWrite(ledPin, LOW); // turn LED off
Serial.println("JUMP"); // notify the Python script
}
// Save the current state so we can detect the next change
lastSwitchState = currentSwitchState;
}
}
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- The Python timeout logic uses time.time() to track the moment of the last landing. The music continues as long as landings arrive within the threshold window:
if line == "LANDED":
# Foil patches made contact — reset the timer and start music
last_landing = time.time()
start_music()
# If music is playing but no landing has come in within TIMEOUT seconds, stop
if playing and (time.time() - last_landing > TIMEOUT):
stop_music()
6. Reflection
This project pushed me to think about interaction in a much more physical way than usual. The main technical challenge was dealing with pin floating — when only one foil patch was touched, the unconnected pin would pick up ambient electrical noise from the environment and the body, triggering false readings. Understanding why INPUT_PULLUP solves this (by giving the pin a definite default state rather than leaving it undefined) was the key insight. The two-stage debounce was also a lesson in how unreliable physical contacts can be at the moment of touch — foil crinkles and makes intermittent contact before settling, and reading the pin twice filtered that out cleanly. Physically, the strain relief on the wires (taping them to the leg with slack at the ankle) turned out to be just as important as the electronics, since a pulled wire mid-jump would break the circuit unpredictably.
One thing I should have considered more carefully from the start was my nephew’s impatience. The whole project was inspired by him, but toddlers don’t wait; if the music doesn’t start immediately or cuts out too quickly between jumps, the experience breaks down fast. In hindsight, I would have tuned the TIMEOUT value with him in mind from the beginning, giving a little more grace time between landings to account for the unpredictable rhythm of a small child jumping rather than calibrating it around an adult’s pace.
