Micropython Mqtt Streamer

Hello everyone, I have developed a micropython code to stream accelerometer data over mqtt. Also I have created a tool to visualize the data which is transferred from remote MQTT device which is executing micropython code.

Demo

Development

The first thing which I tried with micropython is connecting ESP8266 to a WiFi. I have tried the following script which I found from the official documentation of the micropython.

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import network
wlan = network.WLAN(network.STA_IF)
wlan.active(True)
wlan.connect('ssid', 'password')

The wifi ip of the module can be examined with wlan.ifconfig() command. I should say that scripting with a microcontoller is quite fun. ESP8266 was connected over usb over Uart line to my computer and I can scripting using micropython shell. For example: I have used upip module to install umqtt.simple upython module to my ESP8266. After installing the umqtt module, I have tested its basic examples and they worked without any problem.

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>>> import upip
>>> dir(upip)
['__class__', '__name__', 'errno', 'gc', 'help', 'json', 'os', 'sys', 'usocket', 'ussl', 'uzlib', 'main', 'debug', 'tarfile', 'install_path', 'cleanup_files', 'gzdict_sz', 'file_buf', 'NotFoundError', 'op_split', 'op_basename', '_makedirs', 'save_file', 'install_tar', 'expandhome', 'warn_ussl', 'url_open', 'get_pkg_metadata', 'fatal', 'install_pkg', 'install', 'get_install_path', 'cleanup']
>>> upip.install("umqtt.simple")

Next phase is reading data from accelerometer. I have used MPU6050 as the IMU sensor. It consists a gyro and an accelerometer sensor. I have used i2c scanner example code to detect the i2c address of the device. The address of my MPU6050 is 0x68.

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>>> i2c.scan() 
# scan for slaves on the bus, 
# returning a list of valid addresses
>>> for device in devices:
...     print("Decimal address: ",device," | Hexa address: ",hex(device))
...
...
...
Decimal address:  104  | Hexa address:  0x68

The following class is developed to read sensor values directly from MPU6050.

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import machine


class accel():
    def __init__(self, i2c, addr=0x68):
        self.iic = i2c
        self.addr = addr
        self.iic.start()
        self.iic.writeto(self.addr, bytearray([107, 0]))
        self.iic.stop()

    def get_raw_values(self):
        self.iic.start()
        a = self.iic.readfrom_mem(self.addr, 0x3B, 14)
        self.iic.stop()
        return a

    def get_ints(self):
        b = self.get_raw_values()
        c = []
        for i in b:
            c.append(i)
        return c

    def bytes_toint(self, firstbyte, secondbyte):
        if not firstbyte & 0x80:
            return firstbyte << 8 | secondbyte
        return - (((firstbyte ^ 255) << 8) | (secondbyte ^ 255) + 1)

    def get_values(self):
        raw_ints = self.get_raw_values()
        vals = {}
        vals["AcX"] = self.bytes_toint(raw_ints[0], raw_ints[1])
        vals["AcY"] = self.bytes_toint(raw_ints[2], raw_ints[3])
        vals["AcZ"] = self.bytes_toint(raw_ints[4], raw_ints[5])
        vals["Tmp"] = self.bytes_toint(raw_ints[6], raw_ints[7]) / 340.00 + 36.53
        vals["GyX"] = self.bytes_toint(raw_ints[8], raw_ints[9])
        vals["GyY"] = self.bytes_toint(raw_ints[10], raw_ints[11])
        vals["GyZ"] = self.bytes_toint(raw_ints[12], raw_ints[13])
        return vals  # returned in range of Int16
        # -32768 to 32767

    def val_test(self):  # ONLY FOR TESTING! Also, fast reading sometimes crashes IIC
        from time import sleep
        while 1:
            print(self.get_values())
            sleep(0.05)

Main loop is also quite strait-forward. It read samples from acc and send these over mqtt protocol directly to the server.

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from machine import I2C, Pin
import mpu6050
from umqtt.simple import MQTTClient
import time, json

i2c = I2C(scl=Pin(5), sda=Pin(4))
accelerometer = mpu6050.accel(i2c)
c = MQTTClient("umqtt_client", "iot.eclipse.org")
c.connect()

def run():
    while True:
        c.publish( b"micropython/test/mpu6050", json.dumps(accelerometer.get_values()) )
        time.sleep_ms(45)
run()

The code can be reached from this github repo.

References