POOM MIDI Lab: Motion Becomes Music

First, what is MIDI?

MIDI means:

Musical Instrument Digital Interface

The most important idea is:

MIDI is not audio.

POOM does not send the sound of a drum, piano, or synthesizer over Bluetooth. It sends musical instructions such as:

• play this note;
• stop playing this note;
• play it with this intensity;
• change a control or instrument parameter.

Note ON
C4
Velocity 90

This message does not contain a piano recording. It means something like: "Play this note with this intensity."

GarageBand decides how the event sounds. Select a piano and you hear a piano. Select drums and you hear percussion. Choose a synthesizer and the same event creates a different sound.

The controller and the instrument do not need to be the same thing. Our controller is especially unusual: it has no keys. It has motion.

The accelerometer is our instrument

POOM observes acceleration on the X, Y, and Z axes. Those measurements are not music by themselves; the firmware must interpret them.

For example, the firmware can detect that a movement is strong enough to count as a hit, then generate a MIDI note.

1. POOM detects movement.
2. The accelerometer provides data.
3. The firmware analyzes its intensity.
4. POOM decides whether the motion represents an event.
5. POOM generates a MIDI note.
6. The event travels over BLE.
7. GarageBand receives the event.
8. The selected instrument generates sound.

The experiment is about turning physical motion into a musical action.

MIDI over Bluetooth

POOM does not need a USB connection to the iPhone, iPad, or computer while you play. It detects motion and sends BLE MIDI events; the music app generates the audio.

Enter the MIDI Lab

1. On POOM, open THE ZEN from the main menu.
2. Select MIDI and press A.

Opening the app starts:

poom_air_drums

POOM begins reading the accelerometer and starts its BLE MIDI service. The screen displays the Bluetooth state:

BLE: PAIRING

This means POOM is waiting for another device. After a phone, tablet, or computer connects, it changes to:

BLE: CONNECTED

The screen also shows MIDI parameters such as:

Note: C4=60
Thr
DRUM
MELODY MAJOR
MELODY MINOR

Play POOM through the browser piano

You can hear POOM without installing a DAW. The mini player below connects directly over BLE MIDI and turns every incoming note into a piano sound.

First, configure POOM for C major:

1. On POOM, open THE ZEN, select MIDI, and press A.
2. Use UP / DOWN to select Note, then set it to C4=60.
3. Select Mode / Melody, then set it to Melody:MAJOR.
4. Confirm that POOM displays BLE: PAIRING.
5. Press Connect POOM in the piano and choose poom-midi.

Air Drums

DRUM is the easiest mode for your first experiment. Imagine POOM as an invisible drumstick.

Move POOM. The accelerometer measures the motion. If its intensity crosses the configured threshold, the firmware generates a MIDI note.

Hit in the air
Accelerometer
Detection
MIDI event
GarageBand
Sound

You do not need a physical drum or even a surface to hit. Try short movements, wider swings, following a song's rhythm, or moving your whole body.

Is it the world's most serious musical instrument? Probably not. Is it fun? Definitely.

The motion threshold

Thr is the detection threshold. It matters because the accelerometer measures continuously, and even a stationary POOM produces tiny variations.

The sensor only reports numbers:

Ax = ...
Ay = ...
Az = ...

The firmware decides when those numbers mean "this was an important movement" and then "this movement should become a MIDI note."

That small decision is what transforms a sensor into an application.

Melody modes

MELODY MAJOR and MELODY MINOR move beyond drum hits. Your gestures generate notes from different scales.

You do not need music theory to begin. Move POOM, listen, change the note or mode, and move it again. You may find a combination that sounds good almost by accident.

Play with notes until you discover something interesting.

Controls

You can change parameters while playing. The current menu is designed for live experimentation; these values are not persistent presets saved to the microSD card or device memory.

What does Panic mean?

A MIDI note normally uses a pair of events:

NOTE ON
NOTE OFF

During testing, a note may remain active if its corresponding Note Off event does not arrive. The result is a sound that continues indefinitely.

Press A to send:

ALL NOTES OFF

It is a quick way to say: "Stop everything that is playing."

Try it with GarageBand

1. On POOM, open THE ZEN, select MIDI, and press A.
2. Wait for POOM to display BLE: PAIRING.
3. Open GarageBand on your iPhone or iPad.
4. Choose an instrument such as drums, piano, percussion, or a synthesizer.
5. Open GarageBand's Bluetooth MIDI device browser and connect to POOM.
6. Confirm that POOM displays BLE: CONNECTED.
7. Move POOM and listen.

Try short and strong movements. Adjust Thr, change the note, switch to a melody mode, and choose another GarageBand instrument.

There is no single correct way to play it. This is an experiment.

The same motion can sound completely different

Make exactly the same gesture with POOM while GarageBand uses drums. You hear percussion. Change to a piano, and the same motion produces a piano note. Change again, and it becomes a synthesizer.

POOM did the same thing each time: it detected motion and sent a MIDI event. The receiving instrument changed how that event sounded.

You also do not need to keep touching or watching the phone. GarageBand can remain open while POOM becomes the controller:

Motion
POOM
MIDI
Sound

From motion data to music

In the Maker PLOT lab, we observe accelerometer signals and watch the values change when POOM moves. Here, we take the next step. We do not only want to see the signal; we want to do something with it.

1. Measure motion.
2. Interpret the data.
3. Detect an event.
4. Generate MIDI.
5. Let the instrument generate sound.

This is how many embedded applications begin: collect sensor data, give it meaning, and use that meaning to control something.

Where could this go next?

The current firmware is a foundation for experimentation. Future versions could map:

• upward and downward gestures to different notes;
• rotation to instrument or effect changes;
• motion intensity to MIDI velocity;
• orientation to different sounds;
• gestures to chords;
• continuous movement to effect controls;
• two POOM devices to two drumsticks;
• accelerometer and gyroscope data to a complete motion instrument.

Motion
Orientation
Rotation

All of that information can become MIDI control.

Build your own instrument

This experiment shows how an electronic drum kit or a completely new instrument could begin:

Sensor
MIDI event

From there, add:

Pads
Sensors
Hits
Velocity
Gestures
Buttons
Effects

It does not need to become a drum kit. It can become any instrument you can imagine.