1. MQTT & Raspberry Pi Managing Networked Sensors
while Dealing with Jargon
and
(if all goes well)
a net-connected cowbell
Stewart Russell

2. “Back in the old days …”
Coal Clough Wind Farm - Photo by James Bird, CC-BY-ND

3. MQTT Stands for MQ Telemetry Transport
Only faintly related to IBM’s MQ message queue product
Allows sensors to talk over TCP/IP
As standard as we’re likely to see:
ISO/IEC 20922:2016
OASIS standard, 2015
Widely (but quietly) used
Extraordinarily jargon-heavy

4. MQTT Basic Jargon

5. MQTT Topic Hierarchy
Topics have levels: home/basement/temperature home/basement/humidity home/kitchen/temperature …
Wildcard + matches one level: home/+/temperature → home/basement/temperature → home/kitchen/temperature
Wildcard # matches all levels: home/#

6. MQTT: “they thought of that”
Quality of Service: each message can be sent
At most once: typical for most IoT sensors
At least once: may be sent multiple times — important alarms
Exactly once: receipt is verified — valuable transactions
Last Will
A client can register a “will” with the broker should it exit unexpectedly
The broker publishes the will as a message for other clients to act upon

7. Installing a broker Eclipse Mosquitto™ — https://mosquitto.org/
doesn’t seem to require any configuration
small and quite well-behaved
default port 1883
Raspbian installation: sudo apt install mosquitto mosquitto-clients

8. MQTT “Hello, World!”
On the broker host: mosquitto_sub --topic 'hello/#'
On another (or same host): mosquitto_pub [ --host broker_host ] --topic 'hello/world' --message "Hello, World!"
Displayed on the broker host: Hello, World!

9. ESP8266 Wireless sensor board 80 – 160 MHz 32-bit core
Multiple digital I/O ports
One (slightly weedy) 0 – 1 V ADC
Can be very cheap: < $5 / unit
Sold under many names: NodeMCU, Huzzah, ESP8266 Thing, WiPy (v1.0)
Can be programmed in Lua, Arduino, MicroPython, …
By Sparkfun Electronics -
CC BY 2.0,

10. MicroPython Real Python 3 — only smaller!
Runs on many µc boards from ARM Cortex-M0 up
Small memory footprint: can run in under 64 KB RAM
Actively targets ESP8266
Many libraries for supporting different sensors/protocols
Downside: can’t exactly be called fast …

11. Installing MicroPython
Download binary image from
Install over USB serial using esptool.py: sudo pip install esptool
Provides MicroPython REPL over USB serial at bps
(Optionally) provides MicroPython REPL over WebSockets terminal to browser (configuration required)

12. ampy, a serial helper Install via pip install adafruit-ampy
Uploads and downloads program and data files
Manages file folders on your ESP8266
Runs MicroPython scripts with output to the terminal
Examples: ampy -p /dev/ttyUSB2 get boot.py > boot.py ampy -p /dev/ttyUSB2 put main-esp8266-MQTT-DHT22-pin4.py /main.py

13. MicroPython User Interface
Typically through two scripts:
boot.py — board and network setup
main.py — user program

14. boot.py def do_connect(): import network
sta_if = network.WLAN(network.STA_IF)
ap_if = network.WLAN(network.AP_IF)
if ap_if.active():
ap_if.active(False)
print("AP turned off ...")
if not sta_if.isconnected():
print('connecting to network...')
sta_if.active(True)
sta_if.connect('SSID', 'PASSWORD')
while not sta_if.isconnected():
pass
print('network config:', sta_if.ifconfig())
print("Starting network ...")
do_connect()

15. Sensor Setup
DHT22:
Cheap temperature (°C) and relative humidity sensor (%)
Simple one-wire digital protocol
Results to 1 decimal place
Max 1 reading / 2 s
Can be cranky and decides not to give you a reading sometimes (in MicroPython, at least)

16. main.py: 1 of 2 import machine import dht import time
from umqtt.simple import MQTTClient
broker_ip = ' ' # broker address
client_id = 'wemos024155' print('broker: ', broker_ip)
print('client_id: ', client_id)
client = MQTTClient(client_id, broker_ip)
d = dht.DHT22(machine.Pin(4))

17. main.py: 2 of 2 while True: time.sleep(5)
retry = # retry reading if DHT22 stubborn
while retry < 3:
try:
d.measure()
break
except:
retry = retry + 1
if retry < 3:
print(("%6.1f deg C / %6.1f %% RH") % (d.temperature(), d.humidity()))
client.connect()
client.publish(client_id + '/temperature', str(d.temperature()))
client.publish(client_id + '/humidity', str(d.humidity()))
client.disconnect()

18. Local Results! Starting network ... connecting to network...
network config: (' ', ' ', ' ', ' ')
broker:
client_id: wemos024155
20.1 deg C / % RH
20.2 deg C / % RH
20.1 deg C / % RH …

19. Network Results!
$ mosquitto_sub -h v --topic 'wemos024155/+'
wemos024155/temperature 20.6
wemos024155/humidity 30.4
wemos024155/humidity 30.3
wemos024155/humidity …

20. Overnight Results
From mqtt-spy

21. Consuming and Creating
In Python, Eclipse Paho MQTT Python client library: sudo pip install paho-mqtt
This next demo was created using
paho-mqtt for Python 3
GPIO Zero
MicroPython

22. 🐮🔔

23. But seriously … BlueLine PowerCost Monitor
Clips to Smart Meter and gives power readings every 30 s
Given away free by the power authority
Talks over 433 MHz RF
Doesn’t connect to your network ☹
→ just as well we reverse-engineered the protocol! ☺
→ stable Arduino implementation over serial
Almost the perfect application for a small MQTT device