SI7021 I2C sensor
tobru last edited by
I'm trying to get the SI7021 sensor working, which is connected on the I2C bus. Connectivity basically works and I can also write and read bytes. But I strugle with converting the example Arduino code to MicroPython. I've also found another example using the smbus Python library, but I also couldn't find out how to convert this.
Here is what I've done so far:
from machine import I2C import time ADDR = 0x40 SI7021_MEASTEMP_NOHOLD_CMD = 0xF3 SI7021_MEASRH_NOHOLD_CMD = 0xF5 # configure the I2C bus i2c = I2C(0, I2C.MASTER, baudrate=100000) # Humidity i2c.writeto(ADDR, bytes([SI7021_MEASRH_NOHOLD_CMD])) time.sleep(0.3) hum0 = i2c.readfrom(ADDR, 1) hum1 = i2c.readfrom(ADDR, 1) print(hum0) print(hum1) #humidity = ((hum0 * 256 + hum1) * 125 / 65536.0) - 6 #print(humidity) # Temperature i2c.writeto(ADDR, bytes([SI7021_MEASTEMP_NOHOLD_CMD])) time.sleep(0.3) temp0 = i2c.readfrom(ADDR, 1) temp1 = i2c.readfrom(ADDR, 1) print(temp0) print(temp1) #cTemp = ((temp0 * 256 + temp1) * 175.72 / 65536.0) - 46.85 #fTemp = cTemp * 1.8 + 32 #print(cTemp)
b'F' b'F' b'h' b'h'
Currently I don't understand how I can read and convert the data correctly. Sending the commands works and I also get some sort of data back when calling the
i2c.readfromfunction, but then I'm lost. F.e. I don't know how many bytes I must read and then how to convert it to an actual useable value.
Any help is much appreciated!
tobru last edited by
WOW! You're great, works like a charm... Thank you very very much!
from time import sleep_ms from machine import Pin, I2C # Default Address SI7021_I2C_DEFAULT_ADDR = 0x40 # Commands CMD_MEASURE_RELATIVE_HUMIDITY_HOLD_MASTER_MODE = 0xE5 CMD_MEASURE_RELATIVE_HUMIDITY = 0xF5 CMD_MEASURE_TEMPERATURE_HOLD_MASTER_MODE = 0xE3 CMD_MEASURE_TEMPERATURE = 0xF3 CMD_READ_TEMPERATURE_VALUE_FROM_PREVIOUS_RH_MEASUREMENT = 0xE0 CMD_RESET = 0xFE CMD_WRITE_RH_T_USER_REGISTER_1 = 0xE6 CMD_READ_RH_T_USER_REGISTER_1 = 0xE7 CMD_WRITE_HEATER_CONTROL_REGISTER = 0x51 CMD_READ_HEATER_CONTROL_REGISTER = 0x11 class SI7021(object): def __init__(self, i2c=None): self.i2c = i2c self.addr = SI7021_I2C_DEFAULT_ADDR self.cbuffer = bytearray(2) self.cbuffer = 0x00 def write_command(self, command_byte): self.cbuffer = command_byte self.i2c.writeto(self.addr, self.cbuffer) def readTemp(self): self.write_command(CMD_MEASURE_TEMPERATURE) sleep_ms(25) temp = self.i2c.readfrom(self.addr,3) temp2 = temp << 8 temp2 = temp2 | temp return (175.72 * temp2 / 65536) - 46.85 def readRH(self): self.write_command(CMD_MEASURE_RELATIVE_HUMIDITY) sleep_ms(25) rh = self.i2c.readfrom(self.addr, 3) rh2 = rh << 8 rh2 = rh2 | rh return (125 * rh2 / 65536) - 6