Swagbadge2021 MQTT

About MQTT

MQTT is a lightweight message platform that uses individual topics (like a slack channel) that people can send messages to (called publishing) or listen for messages on (called subscribing).

MQTT is designed for use on IoT devices. Check out Wikipedia for some background or mqtt.org for more information on it generally.

About the LCA Swagbadge MQTT server

The badges have MQTT configured to talk to a dedicated server hosted by Andy Gelme, one of the OHMC organisers. We have done this for security and privacy reasons, and because it gives us an Australian server so it's faster.

This server is at 101.181.46.180, the configuration for which is held on the badge at configuration/mqtt.py. The server has some special features:

• The upgrade/ topic path prefix is public read: only Jon and Andy can update it.
• The aiko/ topic path prefix is public read/write
• The public/ topic path prefix is available for everyone to read/write
• The secret/ topic path prefix is write-only
• We have some server monitoring to look for things snooping for all the channels, or who aren't using aiko/on a badge, and mitigations in the event a badge goes beserk and starts a spamming DOS attack.

You are welcome to change which MQTT server your badge uses, by updating the mqtt.py configuration file. Some publicly hosted alternatives are provided (commented out) in the config.

Controlling your badge over MQTT

Making your badge perform

The easiest thing to do is send messages to show up on your screens.

1. Install an mqtt client on your machine
2. Connect to the mqtt server (if you forget what it is, the IP address is shown on bootup)
3. Using your badge's topic (public/esp32_your_badge_id/0/in) send it a message

Messages are usually in the form of (component:command arguments).

mosquitto_sub -h 101.181.46.180 -t public/esp32_id/0 & << does this receive anything?

mosquitto_pub -h 101.181.46.180 -t public/esp32_id/0/in -m "(oled:clear)"

mosquitto_pub -h 101.181.46.180 -t public/esp32_id/0/in -m "(oled:pixel 64 32)"

mosquitto_pub -h 101.181.46.180 -t public/esp32_id/0/in -m "(oled:text 0 50 Hello World)"

OLED messages

(oled:clear)

clears both screens

(oled:log Hello World!)

writes a message along the bottom of the screens, scrolling up whatever is there out of the way

(oled:pixel x y)

lights a pixel at that spot

(oled:text x y This is a test !)

Puts some text at the position x,y. It will be displayed over the top of whatever's there.

If you'd like to make your application MQTT aware, take a look at the oled code.

Using MQTT on your badge

Over Aiko

Aiko has some convenience handlers to make using MQTT easier.

Behind the scenes, Aiko routes messages to the specific handlers matching a given topic and supports multiple handlers “listening” to various specific topics. There is an exception handler wrapped around every message handler, so that the overall MQTT thread doesn’t fail.

Receiving a message and taking action

Subscribe to a topic Update configuration/mqtt.py and add in the topic to the topic_subscribe list

   "topic_subscribe": [ "$me/in", "$me/exec", upgrade_topic, "YOUR_TOPIC" ],

If you want to listen/subscribe to all sub-topics, use a # at the end. For example public/chocolate/# will listen to public/chocolate and public/chocolate/lindt and public/chocolate/kokoblack and public/chocolate/ganache

Handle messages on that topic

Define a message handler function, which takes a topic argument (in case you use the same message handler for multiple topics), and the payload (the message that was seen)

    def on_message(topic, payload_in):
       print(topic + ": " + payload_in)

Add this handler function to the MQTT client: this is typically done in your application's initialise() method.

   mqtt.add_message_handler(on_message, "YOUR_TOPIC")

Publishing a message

Use the aiko mqtt client object to send a message.

  from aiko.mqtt import client
  client.publish(topic, message)

Which topic to use? On our LCA server, we are constrained to only use the 'public' and 'aiko' prefixed topics.

To keep things neat and orderly, we recommend using

public/esp32_SERIAL_ID/YOUR_TOPIC_HERE

for topics specific to your personal swagbadge

public/SUBJECT/YOUR_TOPIC_HERE

for topics intended to share information with multiple swagbadges

Going direct to MQTT

Since Aiko already makes an MQTT connection (to our server), you don’t need to make another MQTT connect, unless you want to interact with multiple MQTT servers (beyond the MQTT server already configured in configuration/mqtt.py.

You can use the Aiko MQTT client object reference to access any of the MQTT library functions …

  >>> import aiko.mqtt.client as mqttclient
  >>> help(aiko.mqtt.client)

All of the available MQTT Client functions

Encrypting messages with your badge

Placeholder text.