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    AHT20 Humidity + Temperature Sensor

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    • J Offline
      JohnGalt @rkorell
      last edited by

      @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

        @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 Reply Quote 0
        • S Offline
          sdetweil @JohnGalt
          last edited by

          @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 Reply Quote 0
          • J Offline
            JohnGalt @sdetweil
            last edited by

            @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 Reply Quote 0
            • S Offline
              sdetweil @JohnGalt
              last edited by

              @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 Reply Quote 0
              • R Offline
                rkorell @JohnGalt
                last edited by rkorell

                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 Reply Quote 0
                • R Offline
                  rkorell @rkorell
                  last edited by rkorell

                  @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

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                  • J Offline
                    JohnGalt @sdetweil
                    last edited by

                    @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.

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

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

                        @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.

                        R 1 Reply Last reply Reply Quote 2
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