ESP32 Weather Station

This is a project with the ESP32 chip onboard the ESP32-DevKitC and a temperature and pressure sensor BMP180. It uses the ESP-IDF framework.

• ESP32 Weather Station
  • Usage
  • Framework
    • Toolchain Troubleshooting (Ubuntu)
    • Project Configuration
    • WiFi
  • Hardware
    • ESP32-DevKitC V4
    • ESP-Prog
      • Pin connection for debugging
    • BMP180 Sensor
  • VS Code Extension

---

Usage

1. Connect the BMP180 to the ESP32-DevKitC. The default pins for I2C are GPIO 19 for SDA and GPIO 18 for SCL. This is set in main.c by calling

   pl_i2c_init(GPIO_NUM_19, GPIO_NUM_18, 100000);

2. The ESP32 needs to connect to an existing WiFi network. See the section Project Configuration for the steps to enter the ssid and the password.
3. Communicate with the ESP32 via UDP. Both sending and receiving are done over the same port. The port and the timer periods for heartbeat and measurements are set in main.c.

   #define UDP_PORT 50000
   #define MEASUREMENT_RATE 600
   #define HEARTBEAT_RATE 300

4. The UDP communication consists of JSON objects that are send as strings. The following listing shows all the current options. The numerical values for the interval variables are in seconds.

   {"type":"get", "quantity":"temperature"}
   {"type":"get", "quantity":"pressure"}
   {"type":"get", "quantity":["temperature", "pressure"]}
   {"type":"set", "name":"heartbeat", "value":"on"}
   {"type":"set", "name":"heartbeat", "value":"off"}
   {"type":"set", "name":"heartbeat_interval", "value": 30}
   {"type":"set", "name":"measurement_interval", "value": 5}

5. The return objects have the following syntax.
   Response to a get request which has only a single element in the list of quantity.

   {
       "type":"response",
       "time":"2021-05-04 20:11:20 CET",
       "quantity": [{
           "name":"temperature",
           "value": 21.5,
           "unit": "celsius"
       }]
   }

   Response from a periodic measurement which holds a list of measured quantities in quantity.

   {
       "type":"measurement",
       "time":"2021-10-18 14:41:29 CET",
       "quantity":[
           {
               "name":"temperature",
               "value": 21.6,
               "unit":"celsius"
           },
           {
               "name":"pressure",
               "value": 1019.310,
               "unit":"hPa"
           }]
   }

   For debug purposes the ESP32 also sends objects with type heartbeat which do not contain any more information than the type and the time.

   {
       "type":"heartbeat",
       "time":"2021-10-18 14:42:53 CET"
   }

6. The UDP traffic is encrypted AES-256-CBC mode. The 32 byte key is set with menuconfig. The buffer length BUFFER_LENGTH in al_crypto determines the length of the outgoing message. The incoming messages can be as large as the BUFFER_LENGTH + 16 for they contain the initialization vector as the first 16 bytes.

---

Framework

The framework used in this project is the ESP-IDF by espressif that can be found on GitHub and has an extensive documentation.
=> https://github.com/espressif/esp-idf
=> https://docs.espressif.com/projects/esp-idf/en/v4.2/esp32/get-started/index.html

This project uses version 4.2 of the ESP-IDF.

git clone --recursive --branch v4.2 https://github.com/espressif/esp-idf.git

Toolchain Troubleshooting (Ubuntu)

Make sure to have the packages python3-virtualenv installed if you have an error No module pip.

The setup needs the name python so set the alternatives.

sudo update-alternatives --install /usr/bin/python python /usr/bin/python3 10 && alias pip=pip3

Then install the toolchain for the local user inside the esp/esp-idf directory by executing

./install.sh

After the installation you need to source esp/esp-idf/export.sh. Create an alias in .bashrc.

alias get-idf='. $HOME/esp/esp-idf/export.sh'

For the gdb debugger to work you have to install the package libpython2.7-dev.

Project Configuration

You can configure the framework for the project in an interactive terminal. Then build, flash and monitor the project. The port for flashing is /dev/ttyUSB0 on Ubuntu.

idf.py set-target esp32
idf.py menuconfig
idf.py build
idf.py flash -p <port>
idf.py monitor -p <port>
idf.py flash monitor -p <port>
idf.py size-components

The WiFi configuration of the menuconfig is located under
Component config ---> Wifi Connect Config ---> WiFi SSID /WiFi Password.
The fast scan method should work fine.

Further documentation for monitor.
=> https://docs.espressif.com/projects/esp-idf/en/v4.2/esp32/api-guides/tools/idf-monitor.html

Notice when writing components:
The following header files are part of esp_common component and do not need to be added to required lists in CMakeLists.txt of components.

• esp_err.h

WiFi

The WiFi bundle uses the LwIP stack with esp_netif and BSD Sockets for UDP/TCP communication. Time synchronization is done via sntp.

=> https://docs.espressif.com/projects/esp-idf/en/v4.2/esp32/api-guides/wifi.html
=> https://docs.espressif.com/projects/esp-idf/en/v4.2/esp32/api-reference/network/esp_netif.html
=> https://docs.espressif.com/projects/esp-idf/en/v4.2/esp32/api-guides/lwip.html
=> https://pubs.opengroup.org/onlinepubs/007908799/xns/socket.html
=> https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/system_time.html?highlight=system%20time

---

Hardware

ESP32-DevKitC V4

Get started with the ESP32-DevKitC V4 board with has the ESP-WROOM-32 chip. The I2C Bus works on 3.3 V.

=> https://docs.espressif.com/projects/esp-idf/en/v4.2/esp32/hw-reference/modules-and-boards.html#esp32-devkitc-v4
=> https://docs.espressif.com/projects/esp-idf/en/v4.2/esp32/hw-reference/modules-and-boards.html#esp-modules-and-boards-esp32-wroom-32

ESP-Prog

For debugging use the ESP-Prog board which has JTAG debugging capabilities. The debugging chip uses two ports:

• /dev/ttyUSB0 is for the JTAG interface and
• /dev/ttyUSB1 for the flashing.

To connect the correct pins see the third link.

=> https://docs.espressif.com/projects/esp-idf/en/v4.2/esp32/api-guides/jtag-debugging/index.html
=> https://github.com/espressif/esp-dev-kits/blob/master/esp-prog/docs/ESP-Prog_guide_en.md
=> https://docs.espressif.com/projects/esp-idf/en/v4.2/esp32/api-guides/jtag-debugging/configure-other-jtag.html
=> https://docs.platformio.org/en/latest/faq.html#faq-udev-rules

Make sure to apply the udev rule to avoid permission issues and then start the openocd service. Note this has to run when starting the gdb.

openocd -f interface/ftdi/esp32_devkitj_v1.cfg -f target/esp32.cfg

You can also flash the ESP32 via JTAG.

openocd -f interface/ftdi/esp32_devkitj_v1.cfg -f target/esp32.cfg -c "program_esp build/esp32-devkitc.bin 0x10000 verify exit"

Start the debugger

xtensa-esp32-elf-gdb -x gdbinit build/esp32-devkitc.elf

Pin connection for debugging

ESP-PROG	DevKit C
TDO	G15
TDI	G12
TCK	G13
TMS	G14
EN	EN
TXD	TXD
RXD	RXD
VDD	3V3
GND	GND
IO0	G0

=> https://github.com/espressif/esp-dev-kits/blob/master/esp-prog/docs/_static/program_pin.png
=> https://github.com/espressif/esp-dev-kits/blob/master/esp-prog/docs/_static/JTAG_pin.png

BMP180 Sensor

Temperature and air pressure sensor with an I2C interface.

• I2C address: 0x77
• I2C clock speed max: 3.4 MHz

---

VS Code Extension

See GitHub on debugging with the extension.

=> https://github.com/espressif/vscode-esp-idf-extension
=> https://github.com/espressif/vscode-esp-idf-extension/blob/master/docs/DEBUGGING.md

Useful settings.json

{
    "idf.port": "/dev/ttyUSB1",
    "idf.adapterTargetName": "esp32",
    "idf.flashType": "UART",
    "idf.openOcdConfigs": [
        "interface/ftdi/esp32_devkitj_v1.cfg",
        "target/esp32.cfg"
    ]
}

Useful launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "GDB",
            "type": "cppdbg",
            "request": "launch",
            "MIMode": "gdb",
            "miDebuggerPath": "${command:espIdf.getXtensaGdb}",
            "program": "${workspaceFolder}/build/${command:espIdf.getProjectName}.elf",
            "cwd": "${workspaceFolder}",
            "environment": [
                {
                    "name": "PATH",
                    "value": "${config:idf.customExtraPaths}"
                }
            ],
            "setupCommands": [
                { "text": "target remote :3333" },
                { "text": "set remote hardware-watchpoint-limit 2"},
                { "text": "mon reset halt" },
                { "text": "thb app_main" },
                { "text": "flushregs" }
            ],
            "externalConsole": false,
            "logging": {
                "exceptions": true,
                "moduleLoad": true,
                "programOutput": true,
                "engineLogging": false,
                "trace": false,
                "traceResponse": false
            },
        }
    ]
}