Show Bluetooth LE Sensor readings on LCD screen connected to STM32

March 14, 2022

The aim of this Bluetooth LE project is to read air quality sensor data and show it on an LCD display which is connected to STM32 board. A web browser will read the sensor data and pass it to STM32 board using BleuIO.

1. Introduction

The project is based on STM32 Nucleo-144 which controls LCD display using BleuIO.

For this project, we will need two BleuIO USB dongles, one connected to the Nucleo board and the other to a computer running the web script and a HibouAir – Air quality monitoring device .
When the BleuIO Dongle is connected to the Nucleo boards USB port the STM32 will recognize it and directly start advertising. This allows the Dongle on the computer port connect with the web script.

With the web script on the computer, we can scan and get air quality sensor data from HibouAir. Then we send these data to LCD screen connected to STM32 using Bluetooth.

We have used a STM32 Nucleo-144 development board with STM32H743ZI MCU (STM32H743ZI micro mbed-Enabled Development Nucleo-144 series ARM® Cortex®-M7 MCU 32-Bit Embedded Evaluation Board) for this example. This development board has a USB host where we connect the BleuIO dongle.

If you want to use another setup you will have to make sure it support USB Host and beware that the GPIO setup might be different and may need to be reconfigured in the .ioc file.

About the Code

The project source code is available at Github.

https://github.com/smart-sensor-devices-ab/stm32_ble_sensor_lcd.git

Either clone the project, or download it as a zip file and unzip it, into your STM32CubeIDE workspace.

If you download the project as a zip file you will need to rename the project folder from ‘stm32_bleuio_lcd-master’ to ‘stm32_bleuio_lcd’

Connect the SDA to PF0 on the Nucleo board and SCL to PF1.

Then setup I2C2 in the STM32Cube ioc file as follows. (Make sure to change the I2C speed frequency to 50 KHz as per LCD display requirements.)

In the USBH_CDC_ReceiveCallback function in USB_HOST\usb_host.c we copy the CDC_RX_Buffer into a external variable called dongle_response that is accessable from the main.c file.

void USBH_CDC_ReceiveCallback(USBH_HandleTypeDef *phost)
{
  	if(phost == &hUsbHostFS)
  	{
  		// Handles the data recived from the USB CDC host, here just printing it out to UART
  		rx_size = USBH_CDC_GetLastReceivedDataSize(phost);
		HAL_UART_Transmit(&huart3, CDC_RX_Buffer, rx_size, HAL_MAX_DELAY);

		// Copy buffer to external dongle_response buffer
		strcpy((char *)dongle_response, (char *)CDC_RX_Buffer);

		// Reset buffer and restart the callback function to receive more data
		memset(CDC_RX_Buffer,0,RX_BUFF_SIZE);
		USBH_CDC_Receive(phost, CDC_RX_Buffer, RX_BUFF_SIZE);
  	}

  	return;
}

In main.c we create a simple intepreter so we can react to the data we are recieving from the dongle.

void dongle_interpreter(uint8_t * input)
{

	if(strlen((char *)input) != 0)
	{
		if(strstr((char *)input, "\r\nADVERTISING...") != NULL)
		{
			isAdvertising = true;
		}
		if(strstr((char *)input, "\r\nADVERTISING STOPPED") != NULL)
		{
			isAdvertising = false;
		}
		if(strstr((char *)input, "\r\nCONNECTED") != NULL)
		{
			isConnected = true;
			HAL_GPIO_WritePin(GPIOE, GPIO_PIN_1, GPIO_PIN_SET);
		}
		if(strstr((char *)input, "\r\nDISCONNECTED") != NULL)
		{
			isConnected = false;
			HAL_GPIO_WritePin(GPIOE, GPIO_PIN_1, GPIO_PIN_RESET);
		}


		if(strstr((char *)input, "L=0") != NULL)
		{

			isLightBulbOn = false;
			//HAL_GPIO_WritePin(Lightbulb_GPIO_Port, Lightbulb_Pin, GPIO_PIN_RESET);
			lcd_clear();

			writeToDongle((uint8_t*)DONGLE_SEND_LIGHT_OFF);

			uart_buf_len = sprintf(uart_tx_buf, "\r\nClear screen\r\n");
			HAL_UART_Transmit(&huart3, (uint8_t *)uart_tx_buf, uart_buf_len, HAL_MAX_DELAY);
		}

		if(strstr((char *)input, "L=1") != NULL)
		{
				isLightBulbOn = true;
				writeToDongle((uint8_t*)DONGLE_SEND_LIGHT_ON);


				lcd_clear();

				lcd_write(input);

		}

	}
	memset(&dongle_response, 0, RSP_SIZE);
}

We put the intepreter function inside the main loop.

/* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */
    MX_USB_HOST_Process();

    /* USER CODE BEGIN 3 */
    // Simple handler for uart input
    handleUartInput(uartStatus);

    // Inteprets the dongle data
    dongle_interpreter(dongle_response);

	// Starts advertising as soon as the Dongle is ready.
	if(!isAdvertising && !isConnected && isBleuIOReady)
	{
		HAL_Delay(200);
		writeToDongle((uint8_t*)DONGLE_CMD_AT_ADVSTART);
		isAdvertising = true;
	}
  }
  /* USER CODE END 3 */

Using the example project

What we will need

Two BleuIO dongles (https://www.bleuio.com/)
A board with a STM32 Microcontroller with a USB port. (A Nucleo-144 development board: NUCLEO-H743ZI2, was used developing this example. (https://www.st.com/en/evaluation-tools/nucleo-h743zi.html)
To connect the dongle to the Nucleo board a “USB A to Micro USB B”-cable with a USB A female-to-female adapter can be used.)

STM32CubeIDE (https://www.st.com/en/development-tools/stm32cubeide.html)
Liquid Crystal Display Module – NHD-0420D3Z-NSW-BBW-V3 (https://www.digikey.com/en/products/detail/newhaven-display-intl/NHD-0420D3Z-NSW-BBW-V3/2626390?s=N4IgTCBcDaIHIAkAiBaADAFjGpBmAWinAMoDqKAQheQGq4gC6AvkA)
HibouAir – Air quality monitoring device (https://www.hibouair.com/)

Importing as an Existing Project

From STM32CubeIDE choose File>Import…

Then choose General>Existing Projects into Workspace then click ‘Next >’

Make sure you’ve choosen your workspace in ‘Select root directory:’

You should see the project “stm32_bleuio_SHT85_example”, check it and click ‘Finish’.

Running the example

Upload the the code to STM32 and run the example. The USB dongle connect to STM32 will start advertising automatically.

Send Sensor data to LCD screen from a web browser

Connect the BleuIO dongle to the computer. Run the web script to connect to the other BleuIO dongle on the STM32. Now you can send sensor data to the LCD screen.

For this script to work, we need

BleuIO USB dongle connected to the computer.
BleuIO javascript library
Chrome 78 or later, and you need to enable the #enable-experimental-web-platform-features flag in chrome://flags
A web bundler – (parcel js)

Create a simple Html file called index.html which will serve as the frontend of the script. This Html file contains some buttons that help connect, read advertised data from the HibouAir to get air quality sensor data, and send this data to the LCD screen which is connected to stm32.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link
      href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/css/bootstrap.min.css"
      rel="stylesheet"
      integrity="sha384-1BmE4kWBq78iYhFldvKuhfTAU6auU8tT94WrHftjDbrCEXSU1oBoqyl2QvZ6jIW3"
      crossorigin="anonymous"
    />
    <title>Bluetooth LE Air quality sensor data to LCD screen</title>
  </head>
  <body class="mt-5">
    <div class="container mt-5">
      <img
        src="https://www.bleuio.com/blog/wp-content/themes/bleuio/images/logo.png"
      />
      <h1 class="mb-5">Bluetooth LE Air quality sensor data to LCD screen</h1>

      <div class="row">
        <div class="col-md-4 pt-5">
          <button class="btn btn-success mb-2" id="connect">Connect</button>
          <form method="post" id="sendDataForm" name="sendMsgForm" hidden>
            <div class="mb-3">
              <label for="sensorID" class="form-label">Sensor ID</label>
              <input
                type="text"
                class="form-control"
                name="sensorID"
                id="sensorID"
                required
                maxlength="60"
                value="0578E0"
              />
            </div>

            <button type="submit" class="btn btn-primary">Get Data</button>
          </form>
          <br />
          <button class="btn btn-danger" id="clearScreen" disabled>
            Clear screen
          </button>
        </div>
        <div class="col-md-8">
          <img src="air_quality_lcd.jpg" class="img-fluid" />
        </div>
      </div>
    </div>

    <script src="script.js"></script>
  </body>
</html>

Create a js file called script.js and include it at the bottom of the Html file. This js file uses the BleuIO js library to write AT commands and communicate with the other dongle.

import * as my_dongle from 'bleuio'
import 'regenerator-runtime/runtime'

const dongleToConnect='[0]40:48:FD:E5:2F:17'
//const sensorID = '0578E0'
document.getElementById('connect').addEventListener('click', function(){
  my_dongle.at_connect()
  document.getElementById("clearScreen").disabled=false;
  document.getElementById("connect").disabled=true;
  document.getElementById("sendDataForm").hidden=false;
})

document.getElementById("sendDataForm").addEventListener("submit", function(event){
    event.preventDefault()
    const sensorID = document.getElementById('sensorID').value
    getSensorData(sensorID)
    setInterval(function () {getSensorData(sensorID)}, 10000);

   
  });

  const getSensorData =((sensorID)=>{
    my_dongle.ati().then((data)=>{
        //make central if not
        if(JSON.stringify(data).includes("Peripheral")){
            console.log('peripheral')
            my_dongle.at_dual().then((x)=>{
                console.log('central now')
            })
        }        
    })
    .then(()=>{
        // connect to dongle
        my_dongle.at_getconn().then((y)=>{
            if(JSON.stringify(y).includes(dongleToConnect)){
                console.log('already connected')
            }else{
                my_dongle.at_gapconnect(dongleToConnect).then(()=>{
                    console.log('connected successfully')
                })
            }
        })
        .then(async()=>{
           return my_dongle.at_findscandata(sensorID,6).then((sd)=>{
                console.log('scandata',sd)
                let advData = sd[sd.length - 1].split(" ").pop()
                let positionOfID= advData.indexOf(sensorID);
                let tempHex = advData.substring(positionOfID+14, positionOfID+18)
                let temp = parseInt('0x'+tempHex.match(/../g).reverse().join(''))/10;

                let co2Hex = advData.substring(positionOfID+38, positionOfID+42)
                let co2 = parseInt('0x'+co2Hex);
                //console.log(temp,co2)
                return {
                    'CO2' :co2,
                    'Temp' :temp,                       
                  }
            })
        })
        .then((x)=>{
            console.log(x.CO2)
            console.log(x.Temp)
            var theVal = "L=1 SENSOR ID "+sensorID+"    TEMPERATURE " + x.Temp + ' °c    CO2 '+ x.CO2+' ppm';
            console.log('Message Send 1 ')
            // send command to show data
            my_dongle.at_spssend(theVal).then(()=>{
                console.log('Message Send '+theVal)
            })
        })
        
    })
})

document.getElementById('clearScreen').addEventListener('click', function(){
    my_dongle.ati().then((data)=>{
        //make central if not
        if(JSON.stringify(data).includes("Peripheral")){
            console.log('peripheral')
            my_dongle.at_central().then((x)=>{
                console.log('central now')
            })
        }
    })
    .then(()=>{
        // connect to dongle
        my_dongle.at_getconn().then((y)=>{
            if(JSON.stringify(y).includes(dongleToConnect)){
                console.log('already connected')
            }else{
                my_dongle.at_gapconnect(dongleToConnect).then(()=>{
                    console.log('connected successfully')
                })
            }
        })
        .then(()=>{
            // send command to clear the screen
            my_dongle.at_spssend('L=0').then(()=>{
                console.log('Screen Cleared')
            })
        })
        
    })
})

The script has a button to connect to COM port on the computer. There is a text field where you can write sensor ID of the air quality monitor device. Once connected, the script will try to get advertised data from the sensor and convert it to a meaningful data. After that it will send this data to the STM32 board which then display on the LCD screen.

To connect to the BleuIO dongle on the STM32, make sure the STM32 is powered up and a BleuIO dongle is connected to it.

Get the MAC address

Follow the steps to get the MAC address of the dongle that is connected to STM32

- Open this site https://bleuio.com/web_terminal.html and click connect to dongle.
- Select the appropriate port to connect.
- Once it says connected, type ATI. This will show dongle information and current status.
- If the dongle is on peripheral role, set it to central by typing AT+CENTRAL
- Now do a gap scan by typing AT+GAPSCAN
- Once you see your dongle on the list ,stop the scan by pressing control+c
- Copy the ID and paste it into the script (script.js) line #4