kwh_display

kwh_display is a project developed in MicroPython aimed at creating a compact display solution using an ESP32 and an ILI9341 screen. The primary functionality of this project is to fetch electricity price data via API and display it on the screen.

Features

• Fetches electricity price data daily when available from an API.
• Inspired by the project PowerDisplayESPHome but developed without any backend dependencies.
• Displays the current day's price alongside tomorrow's price.
• Shows the electricity price in kWh/SEK for the current hour.
• Allows users to select a bidding area (SE 1-4).
• Allows users to customize the price interval.

This project aims to provide a standalone solution for monitoring electricity prices without relying on external services.

ILI9341

Below is the wiring schematic for connecting the ESP32 to the ILI9341 display (2.8 TFT SPI 240x320).

ESP   SSD
---------
3v3   VCC
3v3   LED
GND   GND
IO25  DC
IO26  CS
IO27  RESET
IO14  SCK
IO13  MOSI
IO12  MISO

Casing

/kwh_display/casing holds two STL files avalible for 3D printing the display casing.

ESP32

To use kwh_display, start by flashing the ESP32 with firmware build-ESP32_GENERIC_250330.bin, which is compiled from the MicroPython repository.

Erase and the flash the ESP32 using esptool.

esptool.py --port /dev/ttyUSB0 erase_flash && esptool.py --chip esp32 --port /dev/ttyUSB0 --baud 460800 write_flash -z 0x1000 build-ESP32_GENERIC_250330.bin

Edit /kwh_display/config.json to match your preferred settings. You can customize the price interval to your preference (float). The default price settings are explained in the table below.

Price	Default
Billigt	Price < 0.5
Normalt	0.5 <= Price < 1.5
Dyrt	1.5 <= Price

The case Dyrt is handled by an 'else' statement.

Please note that your WiFi password will be stored in plain text. Proceed with caution.

{
  "ssid": "MySSID",
  "password": "MyPassword",
  "zone": "SE3",
  "url": "http://www.elprisetjustnu.se",
  "api": "/api/v1/prices/",
  "billigt<": 0.5,
  "normalt<": 1.5
}

When the kwh_display boots for the first time it will deploy a hotspot with the SSID kwh_display and host an FTP file server. Access the file server using your preferred method at ftp://192.168.4.1/. After adding config.json to the root of the file system, repower the device.

Troubleshooting

If kwh_display does not boot correctly or if Error! is showing on the display, connect the ESP32 to a serial console. Reboot and analyze the output.

screen /dev/ttyUSB0 115200

The ESP32 has booted correctly if you see output similar to the following in the console:

Boot sequence completed @ <TIME>
Free memory after running gc.collect(): <MEM>

Known Limitations

Currently, it is not possible to adjust the offset price according to power tariffs. Hopefully, this feature will be added in the future.

Development

The kwh_display firmware is compiled from MicroPython using mpbuild. /kwh_display/esp32 code has been “frozen” into the firmware to optimize memory allocation via the /kwh_display/manifest.py file. Drivers were developed by peterhinch. The FTP server was developed by robert-hh.