EE 250L Spring 2018: Example to run MQTT over WiFi with the LPC1768 and ESP8266 devices.

Summary

Demo: https://drive.google.com/file/d/1b-p_HMZK1njtg1B53CgTawzoeTq-ea0S/view?usp=sharing

The main purpose for this repository is to show an educational example of a multi-threaded, (mostly) event-based MQTT application built on top of mbed OS using the ESP8266-01 wifi interface. This code is configured for the mbed LPC1768 board, but should be compatible for other mbed OS capatible boards. Use this repository to help you get started with MQTT. You are in charge of figuring out how to put this together on your m3pi after you get it to work.

Preface

This repository is intended for educational purposes. The code here is heavily commented, and we absolutely welcome any recommendations to improve the code or documentation. Please communicate to us via an issue. Pull requests are welcome!

Overview (to run this example out of the box)

Please go to this link for more information:

https://docs.google.com/presentation/d/1ARA3xXL0szzalFOxm3kWwiWfmI4XSZnZ-C4sqZksHAo/edit#slide=id.g36eca9d95f_0_316

Steps Summary:

1. Update the firmware of the LPC1768 (you need to do this) and ESP8266-01 (this is done)
2. Follow the Fritzing diagram to connect the LPC1768 to the ESP8266-01
3. Edit the MQTT broker hostname and port macros in main.cpp accordingly
4. Configure your mbed_app.json with your wifi SSID and PW
5. Boot everything up. To test if everything is working, publish to the topic m3pi-mqtt-ee250 via our broker on eclipse at port 11000. Use the linux tool mosquitto_pub to do this quickly.

Motivation

1. While mbed OS is well documented with many examples (including examples of using MQTTClient), there is a lack of more complex example applications to illustrate the use of the mbed OS API. In addition, there is not a single place that documents how to run MQTT with an ESP8266 device in mbed OS. This repository is provided to help fill these gaps.

2. Covering ISRs, polling loops, etc. is the first step of learning embedded programming. The next step is to equip students with the ability to program richer applications. Embedded operating systems and programming design patterns can empower students to create these applications with cleaner code. This application example uses the simple dispatcher programming pattern with the use of mbed OS libraries typically available on other embedded OSes. Patterns are hard for students to wrap their head around, and teaching from a book has not shown to be very effective. We have found showing deeper examples illustrating how a pattern is useful and having students develop using the pattern helps students understand their uses and overall create richer applications (with more organized code!). One way to use this repository is start by reading through this example carefully and running the code. Then, use the structure of this example and cater it to your target application.

Powering the ESP8266-01

The ESP8266-01 (or ESP-01) chip takes a 3.3V power supply. Powering it with 5V may burn the chip, so please be careful with this, especially because the LPC1768 has a 5V output right next to the 3.3V output. The ESP-01 needs a clean 3.3V power supply so filtering a 3.3V output from the mbed board with a large capacitor (we have 100uF+ capacitors just in case) will help prevent the ESP-01 from random power cycles. Also, even though the GPIO2 pin is not used, we connect it to VCC (high) to try to further prevent power cycles. We are not quite sure if this matters but we have found many reports of needing to do this on forums.

Updating the mbed LPC1768 and ESP8266-01 Firmware

LPC1768:

Updating the LPC1768 is very simple, and an updated firmware is needed for mbed OS 5+ support. Follow the instructions at this page. The firmware revision we use is 141212.

ESP8266-01:

We have already updated your ESP8266-01. However, if you are interested, here are the instructions on how to do it. Updating the ESP8266-01 (or simply ESP-01) is a more involved process. First, we have found That using an mbed board as a serial passthrough does NOT work very well. It works if you use specific esptool versions and slow down the flash block sizes. Please purchase an FTDI board with a 3.3V output to save you the headache. We specifically used this one from Amazon. Below is a Fritzing diagram of our setup for flashing the ESP8266.

Clone the latest version of the esptool to flash your ESP-01. Also, clone the ESP8266_NONOS_SDK repository to get the AT firmware binaries we used to flash our ESP-01. The ESP8266 comes in very many flavors, and there are many revisions (and manufacturers?) of the ESP-01. We purchased our modules from multiple different vendors on Amazon, and these settings seem to work for all the ESP-01's we've received. Hopefully, the settings and version we successfully used will also work for you. The AT firmware binaries we used were from the master branch at commit 509eae8515793ec62f6501e2783c865f9a8f87e3 of the ESP8266_NONOS_SDK repository. Since we have the 1MB flash variant, we used the binary files listed below. To prepare for flashing, consolidate all the following binary files into one folder (TODO, list paths to these files in the ESP8266_NONOS_SDK repository):

• bin/boot_v1.6.bin
• bin/at/512+512/user1.1024.new.2.bin
• bin/esp_init_data_default.bin
• bin/blank.bin

Before you can flash, you need to boot into the ESP8266's bootloader. To do this, make sure your setup is wired up as shown in the Fritzing diagram above. The key connections is the GPIO0 pin needs to be connected to GND upon reset to boot into the bootloader. Reset the ESP8266 by moving the "RST" pin to GND and then back to 3.3V VCC. Then, flash using the following commands. Make sure to change the port value to the path of your USB to TTL serial adapter:

cd esptool/
./esptool.py --port /dev/ttyUSB0 --baud 115200 write_flash -fm dout -fs 1MB \
-ff 26m 0x00000 ~/ESP8266_NONOS_SDK/bin/boot_v1.6.bin \
0x01000 ~/ESP8266_NONOS_SDK/bin/at/512+512/user1.1024.new.2.bin \
0xfc000 ~/ESP8266_NONOS_SDK/bin/esp_init_data_default.bin \
0x7e000 ~/ESP8266_NONOS_SDK/bin/blank.bin

To test if the flash worked, you can use a serial terminal program like CuteCom with CR,LF line endings and send AT commands. You can refer to Espressif's documentation. Here is a series of commands that will set the ESP8266 to station mode and scan WiFi access points:

AT+CWMODE_CUR=1
AT+CWLAP

Compiling and Running this Example in Linux

It is possible to import this example into the mbed OS online compiler to build. However, we only provide instructions for compiling using mbed-cli. First, install the pre-reqs (mbed-cli only currently supports python2 so please install pip2 using the get-pip.py script that can be found online sudo python2 get-pip.py):

1. sudo pip2 install mbed-cli

2. sudo apt-get install mercurial gcc-arm-none-eabi

3. Install python packages: pip2 install -r requirements.txt

4. Install python, libusb and libncursus (i386 to be compatible with arm-none-eabi-gdb)

    sudo apt-get install python libusb-1.0-0-dev libncurses5:i386
   

5. It might be necessary to update your USB settings to get non-root access to DAP:

    sudo sh -c 'echo SUBSYSTEM==\"usb\", ATTR{idVendor}==\"0d28\", ATTR{idProduct}==\"0204\", MODE:=\"666\" > /etc/udev/rules.d/mbed.rules' 
    sudo /etc/init.d/udev restart 
   

Before compiling, clone this repository or fork the repoisitory and clone your fork. You will be building on top of this example, so do whatever you need to create your own repository using these files. The next step is to initialize the directory into an mbed project and designate the compiler and target.

cd m3pi-mqtt-ee250/
mbed deploy
mbed new .
mbed toolchain GCC_ARM
mbed target LPC1768

We have created a script for you that does a clean compile, flashes, and terms using pyterm that's also in RIOT-OS which we have also included in this repository for your convenience. To run these scripts WITHOUT sudo, you will need to add your user to the dialout group to get access to USB devices. We should not see any use of sudo to flash your LPC1768s!

sudo adduser $USER dialout

Restart your linux machine. If you are using a VM, pass the mbed device through to the guest OS via your Virtualization tool (e.g. Virtualbox). Next, wire up the LPC1768 to the ESP8266 like the Fritzing diagram below:

Once you are finished, return to the code and do the following:

1. Edit the MQTT broker hostname and port macros in main.cpp accordingly
2. Configure the mbed_app.json file with your wifi SSID and PW. Leave the password blank (i.e. "") if it's an open network.

If the ESP8266 is not successfully connecting to your WiFi access point, see the WiFi AP troubleshooting section below. Carefully read the printouts of the connection process to determine if it's really a problem with your AP first!

Then, run the script provided to try to compile, flash, and term. Read through the python script to learn how we do this in case you need to use only a subset of the commands during your development process.

python2 flash_and_term.py

On the first flash, you actually have to manually drop a binary into the LPC1768 before the flashing script fully works. On the first execution of the python script, find the compiled binary file m3pi-mqtt-ee250/BUILD/LPC1768/GCC_ARM/m3pi-mqtt-ee250.bin and drag/drop it directly into the flash drive that pops up when you plug in the LPC1768. Now that a binary file is in there, you should be able to use the flash_and_term.py script to flash your LPC1768 instead of manually dropping in a binary file. Upon every new flash, you will have to press reset button the LPC1768 to start the newly flashed program. Read the printouts to see if the program is able to connect to your wifi access point and our MQTT broker. If it's working, you can start testing if everything is working via MQTT. In a linux terminal, use the mosquitto_pub program to test your connection with the commands below.

First, open a terminal and subscribe to the topic "m3pi-mqtt-ee250/led-thread"

mosquitto_sub -h eclipse.usc.edu -p 11000 -t "m3pi-mqtt-ee250/led-thread"

Then, open another terminal and type this command to trigger the first case in the PrintThread.

echo -ne "\x00\x00" | mosquitto_pub -h eclipse.usc.edu -p 11000 -t "m3pi-mqtt-ee250" -s

Trigger the second case in PrintThread:

echo -ne "\x00\x01" | mosquitto_pub -h eclipse.usc.edu -p 11000 -t "m3pi-mqtt-ee250" -s

Trigger the LEDThread to publish to "m3pi-mqtt-ee250/led-thread" (monitor your susbcriber terminal):

echo -ne "\x01\x00" | mosquitto_pub -h eclipse.usc.edu -p 11000 -t "m3pi-mqtt-ee250" -s

Trigger the LEDThread to turn on LED2 for one second:

echo -ne "\x01\x01" | mosquitto_pub -h eclipse.usc.edu -p 11000 -t "m3pi-mqtt-ee250" -s

Trigger the LEDThread to blink LED2:

echo -ne "\x01\x02" | mosquitto_pub -h eclipse.usc.edu -p 11000 -t "m3pi-mqtt-ee250" -s

If you write a python script to message the mbed in this example, you will have to publish binary data (not a string or binary string). We use raw bytes because it's easier to code on the C++ side. The LPC1768 is an embedded device running C++, so there's no magic!

Understanding the Code

You will need to spend time reading the code, otherwise you won't be able to modify it to suit your application needs. As usual, start at the main() function in main.cpp!

Moving the m3pi Robot

We have provided a movement() function for you to use. If you want to use it in a different .cpp file (e.g. the different thread files), then you can extern the movement() function in that .cpp file to use it. Read the movement() function comments followed by the example we provided and commented out in the main() function. Uncomment the sequence of movement commands, flash the mbed LPC1768, and see how your robot moves!

WiFi AP Troubleshooting

The ESP8266 has very barebones code that may not be handled well by different wierless routers. We've found a lot of problems arise when using password protected access points. Test to see if the ESP8266 can connect to an open network first. If this works, then you may have to change your router's authentication settings. Try all the different WPA authentication types. That is, try WPA with AES, WPA with TKIP, WPA with AES+TKIP, WPA2 with AES, and so on. WiFi Multimedia (WMM) is also known to cause problems with the ESP8266. Turn that setting off in your router.