Published February 11, 2020 © MIT

Fun with ATOM Matrix

Simple MicroPython code for the ATOM 5 x 5 LED matrix and its built-in MPU6886 accelerometer. It works with the M5StickC + NeoFlash Hat.

IntermediateWork in progress2 hours13,514

Things used in this project

Hardware components

M5Stack ATOM Matrix

https://things.lu/product/atom-matrix-esp32-development-kit/

M5Stack M5StickC ESP32-PICO Mini IoT Development Board

https://things.lu/product/m5stickc-development-kit-with-hat/

M5Stack M5StickC NeoFlash Hat

https://things.lu/product/m5stickc-neoflash-hat/

Software apps and online services

MicroPython

Story

During my childhood, I used to have lots of fun putting together electronic contraptions. Every month I browsed the local magazines (yes, we used to have those) looking for projects to build. What a joyful moment when they actually worked - most of the time did they did not.

Anyway, several decades later I've rediscovered this passion by playing with modern microcontrollers during my weekends. My favorite one is the ESP32 from Espressif, specially when programmed with MicroPython.

The ATOM Matrix is the latest and most compact development board in the awesome M5Stack development kit series. It has a built-in MPU6886 accelerometer, which I have used together with my colleague's library to "move" a dot in the device LED Matrix. Both my code and the library has been written in MicroPython and tested with the current 1.12 version.

Hardware

If you use an ATOM Matrix you have everything you will need.

Alternatively this project would also run on a M5StickC - in this case you will need to connect a NeoFlash hat into its back as showed in the picture below.

MicroPython

Connect your ESP32 device to your computer USB port. To check if it has been recognized on Windows you can run device manager (Press the Windows Key and search for device manager).

On device manager a new COM port should be detected as showed in the picture below. Note the COM port that was assigned - we will need that later.

If your computer does not recognize any new USB device, check your cable. If the new device did not install correctly, please manually install the device drivers from the link below.

https://www.ftdichip.com/Drivers/VCP.htm (M5StickC)

Now you are ready to "burn" the MicroPython firmware into the non volatile memory of your device.

You will find the firmware and instructions how to flash it on the official MicroPython site http://micropython.org/download#esp32. I tested the code on this article using the GENERIC firmware esp32-20210418-v1.15.bin.

There is very detailed video explaining all of this in case you prefer to follow along.

VS Code and the Pymakr Plugin

Once you have MicroPython on your device the final step is download and copy main.py and mpu6886.py files to it.

That can be accomplished in different ways my favorite been from Visual Studio Code. You will need an extension developed by Pycom. Instructions can be found here:

https://docs.pycom.io/pymakr/installation/vscode/

To use VS Code with MicroPython, make sure you have a folder containing only the files you want to copy to the device. Open this folder from VS Code and use the Upload command from the Pymakr extension. It will copy all the files from the folder in your computer to the device.

Software

The code basically uses the 3-axis acceleration measurements from the sensor to calculate the Pitch and Roll angles using the formulas from here. Yaw is ignored. If the Pitch / Roll angles are above 5°, the dot moves in that direction. You can adjust the tilt angle needed to move the dot by changing the variable threshold (line 23) - the value is in degrees.

When the dot reaches the LED matrix border it changes color.

I hope you have enjoyed this article and had some fun with it.

# C.LEBOCQ 02/2020
# MicroPython library for the MPU6886 imu ( M5StickC / ATOM Matrix ) 
# Based on https://github.com/m5stack/M5StickC/blob/master/src/utility/MPU6886.cpp

from machine import I2C
from time import sleep

MPU6886_ADDRESS           = const(0x68)
MPU6886_WHOAMI            = const(0x75)
MPU6886_ACCEL_INTEL_CTRL  = const(0x69)
MPU6886_SMPLRT_DIV        = const(0x19)
MPU6886_INT_PIN_CFG       = const(0x37)
MPU6886_INT_ENABLE        = const(0x38)
MPU6886_ACCEL_XOUT_H      = const(0x3B)
MPU6886_ACCEL_XOUT_L      = const(0x3C)
MPU6886_ACCEL_YOUT_H      = const(0x3D)
MPU6886_ACCEL_YOUT_L      = const(0x3E)
MPU6886_ACCEL_ZOUT_H      = const(0x3F)
MPU6886_ACCEL_ZOUT_L      = const(0x40)

MPU6886_TEMP_OUT_H        = const(0x41)
MPU6886_TEMP_OUT_L        = const(0x42)

MPU6886_GYRO_XOUT_H       = const(0x43)
MPU6886_GYRO_XOUT_L       = const(0x44)
MPU6886_GYRO_YOUT_H       = const(0x45)
MPU6886_GYRO_YOUT_L       = const(0x46)
MPU6886_GYRO_ZOUT_H       = const(0x47)
MPU6886_GYRO_ZOUT_L       = const(0x48)

MPU6886_USER_CTRL         = const(0x6A)
MPU6886_PWR_MGMT_1        = const(0x6B)
MPU6886_PWR_MGMT_2        = const(0x6C)
MPU6886_CONFIG            = const(0x1A)
MPU6886_GYRO_CONFIG       = const(0x1B)
MPU6886_ACCEL_CONFIG      = const(0x1C)
MPU6886_ACCEL_CONFIG2     = const(0x1D)
MPU6886_FIFO_EN           = const(0x23)

#consts for Acceleration & Resolution scale
AFS_2G      = const(0x00)
AFS_4G      = const(0x01)
AFS_8G      = const(0x02)
AFS_16G     = const(0x03)

GFS_250DPS  = const(0x00)
GFS_500DPS  = const(0x01)
GFS_1000DPS = const(0x02)
GFS_2000DPS = const(0x03)

class MPU6886():

    def __init__(self, i2c, Gscale = GFS_2000DPS, Ascale = AFS_8G):
        self.i2c = i2c
        self.Gscale = Gscale
        self.Ascale = Ascale
        if self.init():
            self.setAccelFsr(Ascale)
            self.setGyroFsr(Gscale)

    # sleep in ms
    def sleepms(self,n):
        sleep(n / 1000)
    
    # set I2C reg (1 byte)
    def	setReg(self, reg, dat):
        self.i2c.writeto(MPU6886_ADDRESS, bytearray([reg, dat]))
		
    # get I2C reg (1 byte)
    def	getReg(self, reg):
        self.i2c.writeto(MPU6886_ADDRESS, bytearray([reg]))
        t =	self.i2c.readfrom(MPU6886_ADDRESS, 1)
        return t[0]

    # get n reg
    def	getnReg(self, reg, n):
        self.i2c.writeto(MPU6886_ADDRESS, bytearray([reg]))
        t =	self.i2c.readfrom(MPU6886_ADDRESS, n)
        return t    

    def init(self):
        tempdata = self.getReg(MPU6886_WHOAMI)
        if tempdata != 0x19:
            return False
        self.sleepms(1)
        regdata = 0x00
        self.setReg(MPU6886_PWR_MGMT_1, regdata)
        self.sleepms(10)      
        regdata = (0x01<<7)
        self.setReg(MPU6886_PWR_MGMT_1, regdata)
        self.sleepms(10)
        regdata = (0x01<<0)
        self.setReg(MPU6886_PWR_MGMT_1, regdata)
        self.sleepms(10)
        regdata = 0x10
        self.setReg(MPU6886_ACCEL_CONFIG, regdata)
        self.sleepms(1)
        regdata = 0x18
        self.setReg(MPU6886_GYRO_CONFIG, regdata)
        self.sleepms(1)
        regdata = 0x01
        self.setReg(MPU6886_CONFIG, regdata)
        self.sleepms(1)
        regdata = 0x05
        self.setReg(MPU6886_SMPLRT_DIV, regdata)
        self.sleepms(1)
        regdata = 0x00
        self.setReg(MPU6886_INT_ENABLE, regdata)
        self.sleepms(1)
        regdata = 0x00
        self.setReg(MPU6886_ACCEL_CONFIG2, regdata)
        self.sleepms(1)
        regdata = 0x00
        self.setReg(MPU6886_USER_CTRL, regdata)
        self.sleepms(1)
        regdata = 0x00
        self.setReg(MPU6886_FIFO_EN, regdata)
        self.sleepms(1)
        regdata = 0x22
        self.setReg(MPU6886_INT_PIN_CFG, regdata)
        self.sleepms(1)
        regdata = 0x01
        self.setReg(MPU6886_INT_ENABLE, regdata)
        self.sleepms(100)
        self.getGres()
        self.getAres()
        return True      

    def getGres(self):
        if self.Gscale == GFS_250DPS:
            self.gRes = 250.0 / 32768.0
        elif self.Gscale == GFS_500DPS:
            self.gRes = 500.0/32768.0
        elif self.Gscale == GFS_1000DPS:
            self.gRes = 1000.0/32768.0
        elif self.Gscale == GFS_2000DPS:
            self.gRes = 2000.0/32768.0
        else:
            self.gRes = 250.0/32768.0

    def getAres(self):
        if self.Ascale == AFS_2G:
            self.aRes = 2.0/32768.0
        elif self.Ascale == AFS_4G:
            self.aRes = 4.0/32768.0
        elif self.Ascale == AFS_8G: 
            self.aRes = 8.0/32768.0
        elif self.Ascale == AFS_16G:
            self.aRes = 16.0/32768.0
        else:
            self.aRes = 2.0/32768.0

    def getAccelAdc(self):
        buf = self.getnReg(MPU6886_ACCEL_XOUT_H,6)
                   
        ax = (buf[0]<<8) | buf[1]
        ay = (buf[2]<<8) | buf[3]
        az = (buf[4]<<8) | buf[5]
        return ax,ay,az

    def getAccelData(self):
        ax,ay,az = self.getAccelAdc()
        if ax > 32768:
            ax -= 65536
        if ay > 32768:
            ay -= 65536
        if az > 32768:
            az -= 65536
        ax *=  self.aRes
        ay *=  self.aRes
        az *=  self.aRes
        return ax,ay,az

    def getGyroAdc(self):
        buf = self.getnReg(MPU6886_GYRO_XOUT_H,6)
        gx = (buf[0]<<8) | buf[1]  
        gy = (buf[2]<<8) | buf[3]  
        gz = (buf[4]<<8) | buf[5]
        return gx,gy,gz

    def getGyroData(self):
        gx,gy,gz = self.getGyroAdc()
        if gx > 32768:
            gx -= 65536
        if gy > 32768:
            gy -= 65536
        if gz > 32768:
            gz -= 65536 
        gx *= self.gRes
        gy *= self.gRes
        gz *= self.gRes
        return gx, gy, gz 

    def getTempAdc(self):
        buf = self.getnReg(MPU6886_TEMP_OUT_H,2)
        return (buf[0]<<8) | buf[1]  

    def getTempData(self):
        return self.getTempAdc() / 326.8 + 25.0

    def setGyroFsr(self,scale):
        regdata = (scale<<3)
        self.setReg(MPU6886_GYRO_CONFIG, regdata)
        self.sleepms(10)
        self.Gscale = scale
        self.getGres()

    def setAccelFsr(self,scale):
        regdata = (scale<<3)
        self.setReg(MPU6886_ACCEL_CONFIG, regdata)
        self.sleepms(10)
        self.Ascale = scale
        self.getAres()

from mpu6886 import MPU6886
from neopixel import NeoPixel
from machine import Pin, SoftI2C
from time import sleep
from math import *

# Definitions for the ATOM Matrix
LED_GPIO = const(27)
MPU6886_SCL = const(21)
MPU6886_SDA = const(25)
matrix_size_x = const(5)
matrix_size_y = const(5)
is_atom_matrix = True

# Definitions for the M5StickC + NeoFlash hat
#LED_GPIO = const(26)
#MPU6886_SCL = const(22)
#MPU6886_SDA = const(21)
#matrix_size_x = const(18)
#matrix_size_y = const(7)
#is_atom_matrix = False

threshold = const(5) # minimum angle that triggers movement 
color = (0, 0, 20) # Initial color: Blue
x = int(matrix_size_x / 2) # Get matrix
y = int(matrix_size_y / 2) # center
np = NeoPixel(Pin(LED_GPIO), matrix_size_x * matrix_size_y)

def computeAngles(ax,ay,az):
    # https://roboticsclubiitk.github.io/2017/12/21/Beginners-Guide-to-IMU.html
    pitch = 180 * atan (ax/sqrt(ay**2 + az**2))/ pi
    roll = 180 * atan (ay/sqrt(ax**2 + az**2))/ pi
    yaw = 180 * atan (az/sqrt(ax**2 + ay**2))/ pi
    return pitch, roll, yaw

def updateDot(p, angle, size, threshold, color1, color2):
    global color
    if angle > threshold:     # Test if angle is positive
        if p < size - 1:      # If it is not at the matrix
            p = p + 1         # border, move the dot
        else:
            color = color1    # change color if reached the border
    elif angle < - threshold: # Test if angle is negative
        if p > 0:             # If it is not at the matrix
            p = p - 1         # border, move the dot
        else:
            color = color2    # change color if reached the border
    return p

# I2C bus init for MPU6886
i2c = SoftI2C(scl=Pin(MPU6886_SCL), sda=Pin(MPU6886_SDA))

# Values you can use to initialize the accelerometer. AFS_16G, means +-8G sensitivity, and so on
# Larger scale means less precision
AFS_2G      = const(0x00)
AFS_4G      = const(0x01)
AFS_8G      = const(0x02)
AFS_16G     = const(0x03)

# Values you can use to initialize the gyroscope. GFS_2000DPS means 2000 degrees per second sensitivity, and so on
# Larger scale means less precision
GFS_250DPS  = const(0x00)
GFS_500DPS  = const(0x01)
GFS_1000DPS = const(0x02)
GFS_2000DPS = const(0x03)  

# by default, if you initialize MPU6886 with  imu = MPU6886(i2c), GFS_2000DPS and AFS_8G are used
# if you want to initialize with other values you have too use :
# imu = MPU6886(i2c,mpu6886.GFS_250DPS,mpu6886.AFS_4G )
# imu = MPU6886(i2c) #=> use default 8G / 2000DPS
imu = MPU6886(i2c, GFS_500DPS, AFS_4G)

# in order to calibrate Gyroscope you have to put the device on a flat surface
# preferably level with the floor and not touch it during the procedure. (1s for 20 cycles)
#calibrateGyro(20)

while True:
    ax,ay,az = imu.getAccelData()
#    gx,gy,gz = imu.getGyroData()
    pitch, roll, yaw = computeAngles(ax,ay,az)
#    print(ax,ay,az)
#    print(pitch, roll, yaw)
    np[ y * matrix_size_x + x ] = (0,0,0) # Turn off the LED on the current dot possition
    if is_atom_matrix:
        x = updateDot(x, pitch, matrix_size_x, threshold, (20, 0, 0), (20, 20, 0))
        y = updateDot(y, roll, matrix_size_y, threshold, (20, 0, 20), (0, 20, 20))
    else:  # Compensate for the different orientation of the sensor on the M5StickC
        x = updateDot(x, -roll, matrix_size_x, threshold, (20, 0, 0), (20, 20, 0))
        y = updateDot(y, pitch, matrix_size_y, threshold, (20, 0, 20), (0, 20, 20))
    np[ y * matrix_size_x + x ] = color # Turn on the LED on the new dot possition
    np.write()
    sleep(0.2)

Credits

Marcus Tarquinio

1 project • 1 follower

Cédric Lebocq

1 project • 1 follower

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Fun with ATOM Matrix

Fun with ATOM Matrix

Things used in this project

Hardware components

Software apps and online services

Story

Hardware

MicroPython

VS Code and the Pymakr Plugin

Software

Code

mpu6886.py

main.py

Credits

Marcus Tarquinio

Cédric Lebocq

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