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A New Chapter for MagicMirror: The Community Takes the Lead
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AHT20 Humidity + Temperature Sensor

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  • J Offline
    JohnGalt
    last edited by Apr 14, 2025, 9:19 PM

    Does anyone know of a module that will display the output from AHT20 temperature + humidity sensors? I got these after having used the older DHTxx sensors in the past. These new sensors use I2C, and I have confirmed the sensor is wired up correctly and sending data by using an example script.

    Now I’d like to get the output on the Magic Mirror. While I do see some modules that read from I2C compatible sensors, I haven’t seen one that reads these.

    Currently I an working with these two modules, both to no avail:
    MMMiTemperature: https://github.com/Tom-Hirschberger/MMM-Temperature
    and
    MMM-BME280: https://github.com/awitwicki/MMM-BME280

    R 1 Reply Last reply Apr 15, 2025, 6:58 AM Reply Quote 0
    • R Offline
      rkorell @JohnGalt
      last edited by Apr 15, 2025, 6:58 AM

      @JohnGalt Good morning,
      do you have connected the sensors locally to the same PI where the mirror is running?
      What script are you using and what output this sends?
      If you are able to modify these scripts to deliver a JSON output you may can use MMM-JsonValue for displaying the results…

      Regards,
      Ralf

      J 2 Replies Last reply Apr 15, 2025, 6:38 PM Reply Quote 0
      • J Offline
        JohnGalt @rkorell
        last edited by Apr 15, 2025, 6:38 PM

        @rkorell – Thanks for responding, answers follow:

        1. 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).

        2. 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.

        1 Reply Last reply Reply Quote 0
        • J Offline
          JohnGalt @rkorell
          last edited by 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:

          1. Config for this module
          2. Error as captured using pm2 logs
          3. 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
          	} },
          

          Errors [from pm2 logs]:
          0|MagicMirror | [2025-04-15 12:57:48.599] [ERROR] exec error: Error: Command failed: python3 ./modules/MMM-BME280/bme280.py 0x38
          0|MagicMirror | Traceback (most recent call last):
          0|MagicMirror | File “/home/pi/MagicMirror/./modules/MMM-BME280/bme280.py”, line 176, in
          0|MagicMirror | main()
          0|MagicMirror | File “/home/pi/MagicMirror/./modules/MMM-BME280/bme280.py”, line 171, in main
          0|MagicMirror | temperature,pressure,humidity = readBME280All()
          0|MagicMirror | File “/home/pi/MagicMirror/./modules/MMM-BME280/bme280.py”, line 82, in readBME280All
          0|MagicMirror | bus.write_byte_data(addr, REG_CONTROL_HUM, OVERSAMPLE_HUM)
          0|MagicMirror | OSError: [Errno 121] Remote I/O error
          0|MagicMirror |

          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();
                  }
              },
          });
          
          S R 2 Replies Last reply Apr 15, 2025, 8:17 PM Reply Quote 0
          • S Offline
            sdetweil @JohnGalt
            last edited by 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)

            Sam

            How to add modules

            learning how to use browser developers window for css changes

            J 1 Reply Last reply Apr 15, 2025, 8:53 PM Reply Quote 0
            • J Offline
              JohnGalt @sdetweil
              last edited by 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.

              S 1 Reply Last reply Apr 15, 2025, 9:01 PM Reply Quote 0
              • S Offline
                sdetweil @JohnGalt
                last edited by 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

                Sam

                How to add modules

                learning how to use browser developers window for css changes

                J 1 Reply Last reply Apr 16, 2025, 9:47 PM Reply Quote 0
                • R Offline
                  rkorell @JohnGalt
                  last edited by rkorell Apr 16, 2025, 9:58 AM Apr 16, 2025, 9:55 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

                  R J 3 Replies Last reply Apr 16, 2025, 10:35 AM Reply Quote 0
                  • R Offline
                    rkorell @rkorell
                    last edited by rkorell Apr 16, 2025, 10:38 AM Apr 16, 2025, 10:35 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

                    1 Reply Last reply Reply Quote 0
                    • J Offline
                      JohnGalt @sdetweil
                      last edited by 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.

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