AHT20 Humidity + Temperature Sensor

JohnGalt · Apr 15, 2025, 6:38 PM

@rkorell – Thanks for responding, answers follow:

Yes, the first use case is a sensor connected directly to the Raspberry Pi 4 where the Magic Mirror is running. It will be great if I can expand this in the future to display on my office Magic Mirror the outputs from sensors on three (3) other Pis (they run Magic Mirror, NEMS network monitor and Pi-Aware flight tracking, respectively).
I am just running the two Magic Mirror modules listed above. I don’t know what scripts they run. At this point I have just looked and don’t see any obvious way to adapt them. I did try changing the address of the device from their default to 0x38, which is what I think is the address for this sensor attached to my Pi - but I still don’t get output. I should have some time this afternoon to SSH into that machine, and I can locate the scripts and log the error messages.

JohnGalt · Apr 15, 2025, 8:02 PM

@rkorell Ralf: OK, I have a chance to work on this today - Thanks for your help.

To ease troubleshooting, I have temporarily disabled MMM-Temperature and am only running MMM-BME280. Below are the following:

Config for this module
Error as captured using pm2 logs
Code listing of bme280.js, which is called by the module

Config:

{module: 'MMM-BME280', // https://github.com/awitwicki/MMM-BME280
  disabled: false,
  position: 'top_right',
  config: {
    titleText: "Office - MMM-BME280",
    updateInterval: 100, //seconds 
    deviceAddress: "0x38", //0x76 = default
    temperatureScaleType: 1, // 0=Celsius
    pressureScaleType: 1, // 0 = hPa
	} },

Code for bme280.py:

Module.register("MMM-BME280", {
    // Default module config.
    defaults: {
        updateInterval: 100, // Seconds
        titleText: "Home weather",
        deviceAddress: "0x76",
        temperatureScaleType: 0, // Celsuis
        pressureScaleType: 0 // hPa
    },

    // Define start sequence.
    start: function () {
        Log.info("Starting module: " + this.name);

        this.temperature = 'Loading...';
        this.humidity = 'Loading...';
        this.pressure = 'Loading...';

        this.update();
        setInterval(
            this.update.bind(this),
            this.config.updateInterval * 1000);
    },

    update: function () {
        this.sendSocketNotification('REQUEST', this.config);
    },

    getStyles: function () {
        return ['MMM-BME280.css'];
    },

    // Override dom generator.
    getDom: function () {
        var wrapper = document.createElement("div");

        var header = document.createElement("div");
        var label = document.createTextNode(this.config.titleText);
        header.className = 'bme-header';
        header.appendChild(label)
        wrapper.appendChild(header);

        var table = document.createElement("table");
        var tbdy = document.createElement('tbody');
        for (var i = 0; i < 3; i++) {
            var val = "";
            var sufix = "";
            var icon_img = "";

            switch (i) {
                case 0:
                    switch (this.config.temperatureScaleType) {
                        case 0: // Celsius
                            val = this.temperature;
                            sufix = "°C";
                            break;
                        case 1: // Fahrenheit
                            val = Math.round(this.temperature * 9.0 / 5.0 + 32.0);
                            sufix = "°F";
                            break;
                    }
                    icon_img = "temperature-high";
                    break;
                case 1:
                    val = this.humidity;
                    icon_img = "tint";
                    sufix = "%";
                    break;
                case 2:
                    switch (this.config.pressureScaleType) {
                        case 0: // hPa
                            val = this.pressure;
                            sufix = " hPa";
                            break;
                        case 1: // inHg
                            val = Math.round(this.pressure * 100 / 33.864) / 100;
                            sufix = " inHg";
                            break;
                    }
                    icon_img = "tachometer-alt";
                    break;
            }

            var tr = document.createElement('tr');
            var icon = document.createElement("i");

            icon.className = 'fa fa-' + icon_img + ' bme-icon';

            var text_div = document.createElement("div");
            var text = document.createTextNode(" " + val + sufix);
            text_div.className = 'bme-text';
            text_div.appendChild(text);

            var td = document.createElement('td');
            td.className = 'bme-td-icon';
            td.appendChild(icon)
            tr.appendChild(td)

            var td = document.createElement('td');
            td.appendChild(text_div)
            tr.appendChild(td)

            tbdy.appendChild(tr);
        }
        table.appendChild(tbdy);
        wrapper.appendChild(table);

        return wrapper;
    },

    socketNotificationReceived: function (notification, payload) {
        if (notification === 'DATA') {
            this.temperature = payload.temp;
            this.humidity = payload.humidity;
            this.pressure = payload.press;
            this.updateDom();
        }
    },
});

sdetweil · Apr 15, 2025, 8:17 PM

@JohnGalt the module also has a node_helper.js , this is where the python script is launched

browsers cannot access hardware or files directly (for security reasons)

JohnGalt · Apr 15, 2025, 8:53 PM

@sdetweil – Hi Sam, thanks for looking in on this.

I guess I don’t understand… If the module is calling a python script, and the script is polling the sensor - then it would seem to me that the browser isn’t accessing the hardware or files directly. Obviously I’m missing something here.

sdetweil · Apr 15, 2025, 9:01 PM

@JohnGalt the browser (electron) wants to display the data from the sensor, but it cant read it directly. so the module sends a request to the helper to get the data from device 0x38

the module uses a python script to get the data
the python script is reporting an error

that is what needs to be looked at.

you posted the code from the module/browser side which is not involved in getting the actual data

rkorell · Apr 16, 2025, 9:58 AM

the python script you are looking for is bme280.py

#!/usr/bin/python
#--------------------------------------
#    ___  ___  _ ____
#   / _ \/ _ \(_) __/__  __ __
#  / , _/ ___/ /\ \/ _ \/ // /
# /_/|_/_/  /_/___/ .__/\_, /
#                /_/   /___/
#
#           bme280.py
#  Read data from a digital pressure sensor.
#
#  Official datasheet available from :
#  https://www.bosch-sensortec.com/bst/products/all_products/bme280
#
# Author : Matt Hawkins
# Date   : 21/01/2018
#
# https://www.raspberrypi-spy.co.uk/
#
#--------------------------------------
import smbus
import sys
import time
from ctypes import c_short
from ctypes import c_byte
from ctypes import c_ubyte

DEVICE = 0x76 # Default device I2C address

try: #override device address like '0x77'
    DEVICE = int(sys.argv[1], 16)
except:
    pass

bus = smbus.SMBus(1) # Rev 2 Pi, Pi 2 & Pi 3 uses bus 1
                     # Rev 1 Pi uses bus 0

def getShort(data, index):
  # return two bytes from data as a signed 16-bit value
  return c_short((data[index+1] << 8) + data[index]).value

def getUShort(data, index):
  # return two bytes from data as an unsigned 16-bit value
  return (data[index+1] << 8) + data[index]

def getChar(data,index):
  # return one byte from data as a signed char
  result = data[index]
  if result > 127:
    result -= 256
  return result

def getUChar(data,index):
  # return one byte from data as an unsigned char
  result =  data[index] & 0xFF
  return result

def readBME280ID(addr=DEVICE):
  # Chip ID Register Address
  REG_ID     = 0xD0
  (chip_id, chip_version) = bus.read_i2c_block_data(addr, REG_ID, 2)
  return (chip_id, chip_version)

def readBME280All(addr=DEVICE):
  # Register Addresses
  REG_DATA = 0xF7
  REG_CONTROL = 0xF4
  REG_CONFIG  = 0xF5

  REG_CONTROL_HUM = 0xF2
  REG_HUM_MSB = 0xFD
  REG_HUM_LSB = 0xFE

  # Oversample setting - page 27
  OVERSAMPLE_TEMP = 2
  OVERSAMPLE_PRES = 2
  MODE = 1

  # Oversample setting for humidity register - page 26
  OVERSAMPLE_HUM = 2
  bus.write_byte_data(addr, REG_CONTROL_HUM, OVERSAMPLE_HUM)

  control = OVERSAMPLE_TEMP<<5 | OVERSAMPLE_PRES<<2 | MODE
  bus.write_byte_data(addr, REG_CONTROL, control)

  # Read blocks of calibration data from EEPROM
  # See Page 22 data sheet
  cal1 = bus.read_i2c_block_data(addr, 0x88, 24)
  cal2 = bus.read_i2c_block_data(addr, 0xA1, 1)
  cal3 = bus.read_i2c_block_data(addr, 0xE1, 7)

  # Convert byte data to word values
  dig_T1 = getUShort(cal1, 0)
  dig_T2 = getShort(cal1, 2)
  dig_T3 = getShort(cal1, 4)

  dig_P1 = getUShort(cal1, 6)
  dig_P2 = getShort(cal1, 8)
  dig_P3 = getShort(cal1, 10)
  dig_P4 = getShort(cal1, 12)
  dig_P5 = getShort(cal1, 14)
  dig_P6 = getShort(cal1, 16)
  dig_P7 = getShort(cal1, 18)
  dig_P8 = getShort(cal1, 20)
  dig_P9 = getShort(cal1, 22)

  dig_H1 = getUChar(cal2, 0)
  dig_H2 = getShort(cal3, 0)
  dig_H3 = getUChar(cal3, 2)

  dig_H4 = getChar(cal3, 3)
  dig_H4 = (dig_H4 << 24) >> 20
  dig_H4 = dig_H4 | (getChar(cal3, 4) & 0x0F)

  dig_H5 = getChar(cal3, 5)
  dig_H5 = (dig_H5 << 24) >> 20
  dig_H5 = dig_H5 | (getUChar(cal3, 4) >> 4 & 0x0F)

  dig_H6 = getChar(cal3, 6)

  # Wait in ms (Datasheet Appendix B: Measurement time and current calculation)
  wait_time = 1.25 + (2.3 * OVERSAMPLE_TEMP) + ((2.3 * OVERSAMPLE_PRES) + 0.575) + ((2.3 * OVERSAMPLE_HUM)+0.575)
  time.sleep(wait_time/1000)  # Wait the required time  

  # Read temperature/pressure/humidity
  data = bus.read_i2c_block_data(addr, REG_DATA, 8)
  pres_raw = (data[0] << 12) | (data[1] << 4) | (data[2] >> 4)
  temp_raw = (data[3] << 12) | (data[4] << 4) | (data[5] >> 4)
  hum_raw = (data[6] << 8) | data[7]

  #Refine temperature
  var1 = ((((temp_raw>>3)-(dig_T1<<1)))*(dig_T2)) >> 11
  var2 = (((((temp_raw>>4) - (dig_T1)) * ((temp_raw>>4) - (dig_T1))) >> 12) * (dig_T3)) >> 14
  t_fine = var1+var2
  temperature = float(((t_fine * 5) + 128) >> 8);

  # Refine pressure and adjust for temperature
  var1 = t_fine / 2.0 - 64000.0
  var2 = var1 * var1 * dig_P6 / 32768.0
  var2 = var2 + var1 * dig_P5 * 2.0
  var2 = var2 / 4.0 + dig_P4 * 65536.0
  var1 = (dig_P3 * var1 * var1 / 524288.0 + dig_P2 * var1) / 524288.0
  var1 = (1.0 + var1 / 32768.0) * dig_P1
  if var1 == 0:
    pressure=0
  else:
    pressure = 1048576.0 - pres_raw
    pressure = ((pressure - var2 / 4096.0) * 6250.0) / var1
    var1 = dig_P9 * pressure * pressure / 2147483648.0
    var2 = pressure * dig_P8 / 32768.0
    pressure = pressure + (var1 + var2 + dig_P7) / 16.0

  # Refine humidity
  humidity = t_fine - 76800.0
  humidity = (hum_raw - (dig_H4 * 64.0 + dig_H5 / 16384.0 * humidity)) * (dig_H2 / 65536.0 * (1.0 + dig_H6 / 67108864.0 * humidity * (1.0 + dig_H3 / 67108864.0 * humidity)))
  humidity = humidity * (1.0 - dig_H1 * humidity / 524288.0)
  if humidity > 100:
    humidity = 100
  elif humidity < 0:
    humidity = 0

  return temperature/100.0,pressure/100.0,humidity

def main():

  # (chip_id, chip_version) = readBME280ID()
  # print("Chip ID     :", chip_id)
  # print("Version     :", chip_version)

  temperature,pressure,humidity = readBME280All()

  print(round(temperature,1),round(humidity,1),round(pressure,1))

if __name__=="__main__":
   main()

@JohnGalt said in AHT20 Humidity + Temperature Sensor:

Remote I/O error

The given error seems to by not a program but an I/O problem.
I’m not familiar with this sensor so I do not know how to connect and - most important - how to figure out the right “deviceAddress” - it seems that there is the error located.

Either the address isn’t the correct one or the IO channel is somehow broken.
For the latter came in my mind: if this is a I2C conected device - do you have enabled I2C on your Raspi?

I’ve tried to “understand” what happens in the python script above as well as in the C-exmaple program on the Bosch product page for bme280 sensor, but didn’t got it…

Regards,
Ralf

rkorell · Apr 16, 2025, 10:38 AM

@JohnGalt
just seen while re-reading my last posting:

nodehelper.js (the part of the module which is communicating with the python program and so with the sensor) is calling python3 :

exec(`python3 ./modules/MMM-BME280/bme280.py ${deviceAddr}`, (error, stdout) => {

but the python script itself is referencing python 2 (see above post, source code of bme280.py, 1st line:

#!/usr/bin/python

I guess this must match and doesn’t …
So may this is the cause of your problems.

And if this is true it is may really hard to get this working because you may run in several incompatibilities and library-conflicts …

Regards,
Ralf

JohnGalt · Apr 16, 2025, 9:47 PM

@sdetweil – Thanks, Sam. It looks like I intended to send bme280.py but actually copied MMM-BME280.js. I see below where Ralf did post it, so I will look at that, too.

JohnGalt · Apr 16, 2025, 9:57 PM

@rkorell – Hi Ralf:

Yes, I2C is enabled and functioning. There is a test script that does return current temperature and humidity:
Invoking “python AHT20_test.py” does launch this script (Note - I launch from the terminal using ‘python’, not ‘python3’, telling me the system is indeed defaulting to python3):

# SPDX-FileCopyrightText: 2021 ladyada for Adafruit Industries
# SPDX-License-Identifier: MIT

"""
Basic `AHTx0` example test
"""

import time
import board
import adafruit_ahtx0

# Create sensor object, communicating over the board's default I2C bus
i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
sensor = adafruit_ahtx0.AHTx0(i2c)

while True:
    print("\nTemperature: %0.1f C" % sensor.temperature)
    print("Humidity: %0.1f %%" % sensor.relative_humidity)
    time.sleep(2)

JohnGalt · Apr 17, 2025, 1:01 AM

@rkorell + @sdetweil - Thanks for the support. I think I have fixed this for myself by adapting an existing module (“MMM-Temperature”, // https://github.com/Tom-Hirschberger/MMM-Temperature).

That module calls scripts for various sensors to capture the data. I was able to adapt an existing script for use with this sensor, so I think I am good for now.