riza — Smart Massager
A shiatsu massager driven by the muscle it is working on — surface EMG sets the intensity, closing the control loop through the body.
Most massagers ask the user to pick a speed. This one asks the muscle. Electrodes over the muscle belly feed a MyoWare 2.0 sensor, whose envelope output the microcontroller reads as a tension level, and that level drives the massager’s motors: a tense muscle gets a stronger and longer working, a muscle that has relaxed gets backed off.
The loop closes through the body. Massaging changes muscle tension, the sensor sees the change, and the controller responds to it — which makes the system’s own dynamics the research question. How quickly tension falls, how much drive is actually useful, and where the thresholds sit so the loop settles instead of oscillating are the things the current characterisation runs are meant to answer.
The first prototype is built entirely from off-the-shelf parts, so that loop can be studied before any custom hardware is committed to: a MyoWare 2.0 muscle sensor, an Arduino Uno, an L298N H-bridge, and a shiatsu kneading pillow with its stock controller bypassed. Kneading nodes reverse direction periodically, so the motor runs through an H-bridge rather than a single switch.
On boot the firmware measures three seconds of rest and five seconds of maximum voluntary contraction, and those two levels define a normalised tension scale — so the same control law holds across different muscles, electrode placements, and gain settings. It samples the envelope at 200 Hz, updates the control law at 20 Hz, and logs at 10 Hz.