TTN – The Things Network

https://www.thethingsnetwork.org/

Our LoRaWAN sensors use the service of The Things Network. So our LoRaWAN gateway sends the sensor data to the TTN server. The sensors are registered with an ‘application id’ and a ‘device id’.

https://console.thethingsnetwork.org/

Now I want to receive the data on my PC. The TTN server allows to use MQTT.

https://www.thethingsnetwork.org/docs/applications/mqtt/quick-start.html

Note: Currently only the up-topic is working and get the data in JSON format.

https://status.thethings.network/

 

mosquitto – https://mosquitto.org/

Please read the base information on

https://www.thethingsnetwork.org/docs/applications/mqtt/quick-start.html

We want to subscribe using TLS. The access schema seems to be a little bit different. In our case only with the option ‘-L’ it was possible to switch to TLS communication:

mosquitto_sub.exe -L mqtts://<AppID>:<AppKey>@<region>.thethings.network:8883/+/devices/+/up –cafile mqtt-ca.pem

We receive

{
  "app_id":"stm32_example_usi_expansion_board",
  "dev_id":"sensor-ro-20200522",
  "hardware_serial":"E24F43FFFE44C1EF",
  "port":99,"counter":605,
  "payload_raw":"AHMnSwFnARYCaFADAGQEAQAFAdc=",
  "payload_fields":{
    "barometric_pressure_0":1005.9,
    "digital_in_3":100,
    "digital_out_4":0,
    "digital_out_5":215,
    "relative_humidity_2":40,
    "temperature_1":27.8
  },
  "metadata":{
    "time":"2020-07-03T14:02:59.272943586Z",
    "frequency":868.1,
    "modulation":"LORA",
    "data_rate":"SF9BW125",
    "airtime":246784000,
    "coding_rate":"4/5",
    "gateways":[
      {
        "gtw_id":"eui-3133303735005600",
        "timestamp":920207212,
        "time":"",
        "channel":0,
        "rssi":-44,
        "snr":11.75,
        "rf_chain":0
      }
    ]
  }
}

 

Python

Our solution is based on the package paho-mqtt.

https://pypi.org/project/paho-mqtt/

At the first you have to install it to your python environment. Possible you have to update your paket manager at the first.

example Win10: (of course python should be installed already)

cd Python37-32
python -m pip install --upgrade pip
cd scripts
pip install paho-mqtt

Now start the python shell – IDLE (Python 3.7 32-bit)

Load/create the small script mqtt.py. It print the sensor value temperature.

import paho.mqtt.client as mqtt
import json

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print('Connected with result code '+str(rc))
    client.subscribe('+/devices/+/up')

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    ergebnis = json.loads(msg.payload)
    values = ergebnis['payload_fields']
    print(values['temperature_1'])

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message
client.tls_set()
client.username_pw_set('AppId',password='AppKey')

client.connect('eu.thethings.network', 8883, 60)

client.loop_forever()

Of course you have to configure your AppId and AppKey.

Output:

Connected with result code 0
27.9
27.9
27.9
27.9
27.8
27.9
27.8
27.8
27.8
27.8
27.8

 

Intention

ARM provides the possibility to use a printf() like a serial output, using the SWD interface (ITM port 0). This example describes the usage using a Nucleo-64 board, ST-Link v2.1 and the STM32CubeIDE.

Note: The Cortex-M0 doesn’t have the required hardware in the mcu. So it is not possible on it.

switch printf() to the debug interface

Often you find the describtion to overwrite _write(). That’s correct. In case of the STM32CubeIDE generated code it is also possible to overwrite the more low level __io_putchar().

/* USER CODE BEGIN 4 */
int __io_putchar(int ch) {
    ITM_SendChar(ch);
    return ch;
}
/* USER CODE END 4 */

Debug Settings

You have to enable the Serial Wire Viewer (SWV). The most relevant setting is the Core clock. You have to configure the correct clock frequency, that you initialize within your application.

Prepare the Debug view

• Open the SWV ITM Console

printf() uses the SWO connector and the trace port 0.

• Add ITM port 0

• Enable ITM port 0

• Start trace to view the printf() output

That’s all.

Alternative ST-Link Utility