The MyoTyper

Inventor	Lana Novicic
micro:bit IDE	Block Code
Best Location	Classroom

Project Overview

Myotyper is a keyboard that uses EMG technology. Write only by flexing your muscles! It could be hooked up to your leg so you could write without using your arms.

Materials

• 1x Spiker:bit kit (with micro:bit, electrodes, and cables)
• 1x servo motor
• 1x a piece of wood or hard cardboard
• 1x Roll of tape
• 1x big piece of paper
• 1x pen
• 1x clock hand ( thin dowel to fit on servo )

Assembly

1. Choose something you will use a clock hand. It could be a straw, part of a three branch or you can 3D print it! (just make sure it's lightweight).
2. Take a sheet of wood or cardboard and measure and draw a square the size of a servo motor. When that's done, take a pair of scissors and cut the hole. Adjust the hole so that the servo motor fits tightly.
3. Turn the servo motor so that the wires coming out of the motor are oriented towards the end of the wood piece. Glue the motor to the wood.
4. Glue the clock hand to the servo hat to align it with the larger servo motor arm. When it's dried press the servo hat onto the motor.
5. Grab a big piece of paper and measure the middle on one side. Take the wood with the motor and place it like in the picture. Make sure the motor is centered on the paper and the clock hand is facing right, parallel to the edge of the paper. Once it is positioned, tape the wood to the paper.
6. Write the code and come back when you're done. Flex your muscles to move the clock hand and simultaneously write the letters as you move it. writing the code

Coding

1. Set the threshold to 450. Make a variable (here: a) that will count the times the threshold was passed. By setting the variable time to millis we marked the beginning of a time frame. You can also add a play sound block and set it to beep every 2 seconds, to know when to move.
2. Add the while loop and set it like in the code. This allows us to make a time period of 2 seconds that will keep repeating forever. Set the emg to analog read pin 0 (reading emg from electrodes). the variable a is set to change by 1 only when the EMG has passed the threshold, but the previous EMG hasn’t.
3. Next, tell the program to move the clock hand to the starting point “on start”. Then make a list and set it to an array of letters. Make sure you leave the first spot empty (or add some sign).
4. Now we have to assign a role to a different number of muscle contractions. If the muscle is contracted once the clock hand will move by 6 degrees. We add the variable _1click that will increase by 6 every time the clock hand moves.
5. If the muscle is contracted twice the clock hand will move to the beginning. The variable _2click will equal the number of movements (var _1click / 6). Now we just find the letter that has the same value in the array and add it to the variable letter.
6. Lastly we set that if the variable a remains 0 within the timeframe the micro:bit will display the words we wrote.

Below is the completed code in micro:bit makecode python.

slovo = ""
_2click = 0
bgn = 0
_1click = 0
moveby = 0
premg = 0
emg = 0
nadja = 0
vreme = 0
treshold = 0
pins.servo_write_pin(AnalogPin.P8, 0)
text_list = ["!",
    "a",
    "b",
    "c",
    "d",
    "e",
    "f",
    "g",
    "h",
    "i",
    "j",
    "k",
    "l",
    "m",
    "n",
    "o",
    "p",
    "q",
    "r",
    "s",
    "t",
    "u",
    "v",
    "w",
    "x",
    "y",
    "z"]

def on_forever():
    global treshold, vreme, nadja, emg, premg, moveby, _1click, bgn, _2click, slovo
    treshold = 450
    vreme = control.millis()
    nadja = 0
    music.play(music.tone_playable(262, music.beat(BeatFraction.WHOLE)),
        music.PlaybackMode.UNTIL_DONE)
    while control.millis() - vreme < 2000:
        emg = pins.analog_read_pin(AnalogPin.P0)
        if emg >= treshold and premg < treshold:
            nadja += 1
            control.wait_micros(500000)
        premg = emg
        serial.write_line("" + str(nadja))
    if nadja == 1:
        moveby = moveby + 6
        pins.servo_write_pin(AnalogPin.P8, moveby)
        _1click = moveby
    elif nadja == 2:
        bgn = 0
        pins.servo_write_pin(AnalogPin.P8, bgn)
        moveby = 0
        _2click = _1click / 6
        slovo = "" + slovo + text_list[_2click]
    elif nadja == 0:
        basic.show_string(slovo)
        slovo = ""
basic.forever(on_forever)

Operating

• Plug the motor cable into the Spiker:bit (pin 8). Stick the electrodes to your arm or leg and connect them using the orange cable, which should be plugged into pin 0. Download the code onto the micro: bit and start it.
• Relax your arm and squeeze your muscles after every beep to change the letter. When you reach the letter you want to select squeeze twice. After each letter is selected the clock hand will automatically go back to the beginning.
• To write out the word just relax your hand and wait a few seconds and the word should appear on the micro:bit.

Tips

• It takes a bit of time to get used to it but the beat helps in catching the rhythm
• You can also change/adjust the number of muscle contractions for different functions however you like
• change the threshold until it works for you