RPIPicoRTOSMQTT

RPI Pico WIFI via ESP-01S, LWESP, FreeRTOS, and MQTT example

Demo code for RPI Pico using ESP-01S for wifi connection over uart. With MQTT client stack to allow. Pico responds to a ping message and responds with a pong message.

Nothing clever in the code just wrapping the libraries into some C++ classes and domonstrating working example.

Stability of this example is not as good as I would like. Client dies with message rate above 10per second. Recomend looking at the alternative RPIPicoRTOMQTT3 version which uses the lwesp library for MQTT and runs more stably.

Hardware

• Raspberry Pico
• ESP-01S (1Mb) running ESP-AT 2.1

Connections:

PICO Uart0 on GPIO12 and 13

pico	function	ESP-01S	function
G12	TX	RX	RX
G13	RX	TX	TX
3.3	3.3v	3.3	3.3v
GND	GND	GND	GND
3.3	3.3v	EN	via 10k res

ESP-01S

I got very cheap pack of ESP-01S but they came with 1Mb flash. Latest version of ESP-AT, version 2.2, requires 2MB.

Fortunatly Jandrassy has built a working 2.1 firmware for 1MB. This is on github at: https://github.com/jandrassy/WiFiEspAT

To reliably upload the firmware to ESP-01S requires the RST IO0 to get pulled to zero and the released. Some further inform on how to do this at: https://blog.tiga.tech/flashing-esphome-firmware-to-esp-01s/

I used the RPI 4 to upload the firmware and the esptool.py. I had to drop frequency to 40m and change upload mode to dout in the download.config file. Then use the command esptool.py --port /dev/ttyS0 write_flash @download.config

Dependancies

C++

• lwesp: library for talking to ESP-AT over serial
• FreeRTOS-Kernel: dependency for lwesp
• coreMQTT from FreeRTOS: MQTT client library.

I could have used lwesp directly for MQTT but I wanted to move to using SSL and mutual authentication. (Both of which are not in this code, yet).

Configuration for the libraries are within the src/port folders. They are complex libraries and need proting for the Pico.

Python3

I've used the Paho python client to send a ping. See the py folder.

Cloning and build

git clone --recurse-submodules https://github.com/jondurrant/RPIPicoRTOSMQTT

main.cpp include "Credentials.env" for the Wifi AP name and passwd, MQTT Host, Port, Username and password. I've not included this file in the repo. Please create one looking something like this:

#define SID "SID"
#define PASSWD "PWD"

#define MQTTHOST "IP"
#define MQTTPORT 1883
#define MQTTUSER "jon"
#define MQTTPASSWD "PWD"

To build:

cd RPIPicoRTOSMQTT
mkdir build
cd build
cmake ..
make
make install (only work if you used my config setup in the Pico Intro course as does SWD upload of code direct from make).

MQTT Server

I'm using Mosquitto on a RPI. Followed the docker install guide at: https://docs.cedalo.com/streamsheets/2.4/installation/

Clients

Two users are setup on Mosquitto:

• jon - test identity for the pico
• mbp - test identity for my python ping code

Topic Structure

I've tried to condence literals a bit, nervous on memory usage.

TNG// - THING / ID, same as user name in my example TNG//LC - LC is lifecycle and annouces connection and disconnection TNG//TPC - TOPIC, for messaging to a specific thing

Example assuming you keep the pico as "jon"

• TNG/jon/TPC/PING - ping re quest sent to jon
• TNG/jon/TPC/PONG - pong as response to the ping

To Do List

• Make code into a reusable library
• Add support for a twin data structure like AWS Shadow
• SSL Support
• Mutual Authentication