SI7021 I2C pin setup (SOLVED)

robert-hh

@tttadam The board looks fine. Not additional resistors required. In the SI7021 class there is a function call write_command. Change that function into:

def write_command(self, command_byte):
    self.i2c.writeto(self.addr, command_byte)

tttadam

@robert-hh well I ran my little baudrate finder again with modflyed write_command method.
But I got tha same result, exept it frozed at 2964 baud.

I am not sure what am I missing.

robert-hh

@tttadam Don't care about the baud rate. Here is works well at the default baud rate (I purchased I device for testing). This is the class code which works:

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[1] = 0x00
    
  def write_command(self, command_byte):
    self.i2c.writeto(self.addr, command_byte)

  def readTemp(self):
    self.write_command(CMD_MEASURE_TEMPERATURE)
    sleep_ms(25)
    temp = self.i2c.readfrom(self.addr,3)
    temp2 = temp[0] << 8
    temp2 = temp2 | temp[1]
    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[0] << 8
    rh2 = rh2 | rh[1]
    return (125 * rh2 / 65536) - 6

It is called with:

from machine import I2C
i2c=I2C(0, I2C.MASTER)

from SI7021 import SI7021
m = SI7021(i2c)
print(m.readRH(), m.readTemp())

Device connected at P9 = SDA and P10 = SCL, Vin at 3.3V

tttadam

@robert-hh

Traceback (most recent call last):
  File "main.py", line 6, in <module>
  File "/flash/lib/SI7021.py", line 32, in readTemp
OSError: I2C bus error

still the same. If it's working on your side, than my sensor must be dead.

robert-hh

@tttadam Please check that there is only one copy of SI7021.py installed on your device. When working with pymakr, that may happen. Please use simple tools like ftp for the check. And yes, the version I posted works. No, I do not think that your device is defect. And it is well protected. Ans since it responds well to scan(), the wiring is also fine. So the code or code set-up is most probably the problem.

tttadam

@robert-hh Can I do a factory reset somehow? Delete everything from the device.

robert-hh

@tttadam When you update the firmware, then you have in the advanced section the option to erase the file system. Other method from the REPL prompt:

import uos
uos.mkfs("/flash")

And then reboot.

tttadam

@robert-hh Well I formatted the flash, then restarted the device.
Than uploded SI7021.py, an empyt boot file, and a main.py with 6 line of code. But still no luck...

Uploading project (main folder)...
Not safe booting, disabled in settings
Reading file status
Failed to read project status, uploading all files
Creating dir lib
[1/3] Writing file boot.py
[2/3] Writing file lib/SI7021.py
[3/3] Writing file main.py
Upload done, resetting board...
OKets Jun  8 2016 00:22:57

rst:0x7 (TG0WDT_SYS_RESET),boot:0x33 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff8028,len:8
load:0x3fff8030,len:1728
load:0x4009fa00,len:0
load:0x4009fa00,len:14584
entry 0x400a059c
[64]
Traceback (most recent call last):
  File "main.py", line 6, in <module>
  File "/flash/lib/SI7021.py", line 32, in readTemp
OSError: I2C bus error
Pycom MicroPython 1.18.1.r1 [v1.8.6-849-b0520f1] on 2018-08-29; LoPy4 with ESP32
Type "help()" for more information.

my main.py:

from machine import I2C
from SI7021 import SI7021
i2c=I2C(0, I2C.MASTER)
print(i2c.scan())
m = SI7021(i2c)
print(m.readRH(), m.readTemp())

my boot.py, is just comment

and my SI7021 is like this:

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[1] = 0x00
    
  def write_command(self, command_byte):
    self.i2c.writeto(self.addr, command_byte)

  def readTemp(self):
    self.write_command(CMD_MEASURE_TEMPERATURE)
    sleep_ms(25)
    temp = self.i2c.readfrom(self.addr,3)
    temp2 = temp[0] << 8
    temp2 = temp2 | temp[1]
    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[0] << 8
    rh2 = rh2 | rh[1]
    return (125 * rh2 / 65536) - 6

robert-hh

@tttadam It is interesting that readRH() seemed to have worked, since the code fails at readTemp(). Try two things:
a) use only readRH
b) increase the sleep_ms(25) to sleep_ms(50).

tttadam

@robert-hh

YAAAAAY!!! :D
Increasing the sleep_ms to 50 solved it!

[64]
42.83194 26.78852

robert-hh

@tttadam That's very good. When trying to read before the conversion is done you get an I2C bus error. The strange thing is, that according to the data sheet 25ms is already a safe value. The maximum conversion time according to the data sheet is 12 ms for RH at 12 bit resolution.
I found no robust way to scan the device for a "conversion ready" state.

robert-hh

@tttadam I extended the class SI7021 a little bit. It also waits now for max 100ms time for the device to return a value, but returns earlier if values are returned. A documentation is added too.
https://github.com/robert-hh/SI7021

tttadam

@robert-hh Awsome! Thank you

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SI7021 I2C pin setup (SOLVED)

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