WLAN Relays

This repository contains a very simple HTTP server written in MicroPython for controlling pins of an ESP32 board. These pins can be connected to solid state relays to switch lamps for example.

Client Example

The board will start in access-point mode. This means it provides its own WLAN and you have to connect your computer or phone to it first. In this mode, the board always has the IP address 192.168.4.1.

Set pin D22 to low using the HTTP client curl:

curl -v -m 3 -X POST http://192.168.4.1:7005 --data '{"pin22": false}'

You can connect the board to your existing WLAN by entering your WLAN SSID and password into secrets.py. In this mode, your router assigns a new IP address to the board, which is then displayed in the web interface of most routers.

The Hardware

ESP32 DevKit V1 boards have WLAN hardware built-in and run with 5V and only 50mA idle or 130mA while transmitting. Pinouts of common ESP32 boards are here.

A few hundred watts AC can be switched with a 5V DC AC solid state relay. Some of these can be controlled directly by 3.3V output pins. During power-up the ESP32 pins are inputs (have high impedance but 3.3V). To keep relays off until the pins are actively controlled as outputs you can use Low Level Trigger variants (>1V ⇒ off, <1V ⇒ on).

Additional hints

• To reset a ESP32 DevKit V1 board press button "EN"
• To suppress boot messages pull-down Pin D15 to GND with a 10k resistor (helps to avoid problems with terminal tools)
• Pins >=34 are inputs only! (no output on D34, D35)

The Software

The following tutorial works on a Linux Mint 21.x or similar Debian-based Linux like Ubuntu. You can run Linux Mint directly from a Live USB stick without installing it on your computer.

Install the ESP-IDF 5.0.4 build tools (only needed once!):

sudo apt update
sudo apt install git wget flex bison gperf python3 python3-venv cmake ninja-build ccache libffi-dev libssl-dev dfu-util libusb-1.0-0
sudo apt remove brltty                  # stop brltty from stealing /dev/ttyUSBx

mkdir -p ~/esp && cd ~/esp
git clone -b v5.0.4 --recursive https://github.com/espressif/esp-idf.git
cd esp-idf
./install.sh esp32

sudo adduser $USER dialout              # allow access to USB serial devices
# ... and then logout and login again!

Download this project and prepare MicroPython for ESP32 (only needed once!):

mkdir -p ~/git && cd ~/git
git clone https://github.com/oliver-joos/wlan-relays.git
cd wlan-relays
git submodule update --init micropython/

make -C micropython/mpy-cross/
make -C micropython/ports/esp32/ submodules

Setup your terminal (needed once per session!):

source ~/esp/esp-idf/export.sh
export ESPPORT=/dev/ttyUSB0             # or /dev/ttyACM0 for CH9102X USB ICs
export ESPBAUD=921600

Build and deploy the MicroPython firmware image:

make -C micropython/ports/esp32/ clean  # only after changes in micropython/
make -C micropython/ports/esp32/ -j all

make -C micropython/ports/esp32/ PORT=$ESPPORT erase  # only for empty boards
make -C micropython/ports/esp32/ PORT=$ESPPORT deploy

Copy Python files to your board (overwrites existing files!):

./micropython/tools/mpremote/mpremote.py fs cp *.py :/

Now press the reset button on your board!

To see log messages or soft-reset the board you can use the MicroPython REPL interface:

./micropython/tools/mpremote/mpremote.py    # connect to REPL

# press Ctrl+C to abort the application
# press Ctrl+D to soft-reset the system
# press Ctrl+X to exit the mpremote tool