Displaying temperature on the STM32L4 Discovery Kit Board

Question

I am able to send messages from the the STM32L4 Discovery Kit Board to the AWS Cloud as I have gone through the fist steps guide https://docs.aws.amazon.com/freertos/latest/userguide/freertos-prereqs.html. Although now I would like to display sensor data specifically temperature from the board to the cloud, how can I do this?

Accepted Answer

Hi Obinex. You can use the functions in the BSP to access the sensor data. Then construct a JSON document to publish.

The demo you've been using publishes a plaintext message here: https://github.com/aws/amazon-freertos/blob/main/demos/coreMQTT/mqtt_demo_mutual_auth.c#L981-L993

You can find the BSP drivers for the various sensors here: https://github.com/aws/amazon-freertos/tree/main/vendors/st/stm32l475_discovery/BSP/B-L475E-IOT01

So you want some code like this to create a JSON document instead of a plaintext string:

```
        int16_t accel[3], magneto[3];
        float gyro[3];
        BSP_ACCELERO_AccGetXYZ(accel);
        BSP_GYRO_GetXYZ(gyro);
        BSP_MAGNETO_GetXYZ(magneto);

++publishCount;

snprintf(publishPayload, sizeof(publishPayload), "{\"sequence\":%ld"
            ",\"payload\": {"
            "\"temperature\":%.2f"
            ",\"humidity\":%.2f"
            ",\"pressure\":%.2f"
            ",\"accelerometer\":{\"x\":%d,\"y\":%d,\"z\":%d}"
            ",\"gyroscope\":{\"x\":%.2f,\"y\":%.2f,\"z\":%.2f}"
            ",\"magnetometer\":{\"x\":%d,\"y\":%d,\"z\":%d}"
            "}}",
               publishCount,
               BSP_TSENSOR_ReadTemp(),
               BSP_HSENSOR_ReadHumidity(),
               BSP_PSENSOR_ReadPressure(),
               accel[0], accel[1], accel[2],
               gyro[0], gyro[1], gyro[2],
               magneto[0], magneto[1], magneto[2]
               );
```

If you are asking how to display it in the cloud, I suggest you read the following blog. Pattern 4 is one of the simplest ways to get started.

https://aws.amazon.com/blogs/iot/7-patterns-for-iot-data-ingestion-and-visualization-how-to-decide-what-works-best-for-your-use-case/

Displaying temperature on the STM32L4 Discovery Kit Board

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