Re: [mosquitto-dev] MQTT-based voltage sensor

[Josef Möllers <josef.moellers@xxxxxx>]

On 16.10.20 00:33, mohamed Abdulmajid wrote:

hello everyone ,

i'm working on a voltage sensor that reads the input voltage and sends it through MQTT to a mobile application . i need help in the part of the code that is related to publishing the readings to the mqtt broker . 

this is my code : 

That was an awful lot of code and it reached my site not properly formatted:

client.begin(mqtt_server, atoi(mqtt_port), net);

Also, I'm not sure if I understand the idea of setting up an HTTP server to publish MQTT topics.

My code just does this at a fairly low level:

1) set up parameters required like broker IP, broker port, broker username, broker password

2) make a measurement

3) mosquitto_lib_init();

4) mosq = mosquitto_new(client_id, true, NULL);

5) mosquitto_publish_callback_set(mosq, my_publish_callback);    // my_publish_callback just does "outstanding--;"

6) mosquitto_username_pw_set(mosq, username, password)

7) mosquitto_reconnect_delay_set(mosq, 5, 60, 1);

8) mosquitto_connect(mosq, host, port, 60)

9)  mosquitto_publish(mosq, NULL, topic, strlen(m->value), m->value, 1, 1); outstanding++;

10) while (outstanding > 0) mosquitto_loop(mosq, -1, 1);

11) mosquitto_disconnect(mosq);

12) mosquitto_destroy(mosq);

Please read up on the functions in the manual pages.

I usually wrap this into one MQTT-specific source file with another source file containing the sensor-specific code which returns a GList (*) of measurements to publish. I have attached the sources (hehe maybe somebody will point at bugs to me ;-) ). So when I need an MQTT publisher for a new sensor, I just write the new sensor-specific code and be done with it.

Josef

(*)https://developer.gnome.org/glib/stable/glib-Doubly-Linked-Lists.html

Attachment: HTU21D.tgz
Description: application/compressed-tar