Plan to use ESPHome + LVGL instead of Nextion display

[nagyrobi]

Here's my plan to use ESPHome + LVGL instead of Nextion display:

ESPHome is adding support for the LVGL graphics library.
Several screens are supported but for this project a WT32-SC01 Plus would be most suitable because:

• has a pretty nice case that can be mounted on a box which has esp32-evse inside
• has resolution of 480*320
• has capacitive touch screen
• it runs an ESP32-S3
• it has an RS485 transceiver
• has quite some free GPIOs
• less expensive than Nextion

Running ESPHome on it has the following advantages:

• any useful graphical UI can be rendered via LVGL, with fully open source resources (no proprietary editor needed)
• can act as a ModBUS RTU master (or slave) to communicate with esp32-evse, any register can be read or written
• multiple UARTs can be configured (eg one talking to esp32-evse, other talking to smart meter etc)
• can connect to Home Assistant via native API (or MQTT to other systems), can expose any register as a sensor or control to HA
• can use free GPIOs or the display for anything else

With this it becomes possible not only to have a fully customizable UI, but also:

• 1-click integration with Home Assistant, making possible any notifications or remote access through it
• make own Dynamic Load Management through HA or other ESPHome components (eg use data from other meters in various ways; freely implement DLM logic either in HA or in ESPHome)
• implement any custom authorization like RFiD readers etc
• all these just talking with esp32-evse via ModBUS
• esp32-evse will have a free UART which could be used for something else.

As far as I see the ModBUS feature set is wider that Nextion's so it's already possible to implement more functionality with this kind of display that with Nextion out of the box.

As soon as I get my esp32s2-evse-d-a up and running, will start on this and publish the YAML.

[dzurikmiroslav]

Yes, Nextion is quite outdated and their designer is from the Windows XP era :-) This device with LVGL look good 👍

With a Modbus API, the display must periodically pooling registers ​​from the EVSE. Probably in small time interval, which can be reflected in the performance.

Nextion API is designed to you subscribe to value, and EVSE send you once immediately and next time, when its changed value. I don't know if this data format would be suitable for LVGL, but it is not a problem to implement all other values like Modbus API.

Also you can use Netion API thorught RS485 serial, the same also applies to Modbus API, it can also be used via UART serial.

[nagyrobi]

Poll time can be configured at will.
Nextion is a proprietary format, ESPHome can also only send data but not receive aka. emulate a Nextion display. But, could be done in theory, if we had the protocol description.

[dzurikmiroslav]

It's a text format and not very complicated, some small example:

• display send: sub state
• EVSE send: state.txt="A"
• when EV connect EVSE send: state.txt="B0"

[nagyrobi]

Would be nice to have a dump of the communication to see all the variables going back and forth.

However, I still think ModBUS is a better application because I could use a single display to manage multiple EVSE devices, each can have a different address. Moreover, I can make decisions on the same place (the same MCU of the display) when both EVSE want to charge simultaneously to balance load. As the display being driven by an ESP32, it is able to do more complex tasks. It can easily be a master for a network of slave EVSEs (+a smart meter if desired, and implement DLM).

Polling frequency can be changed on demand, eg by default don't poll too often, but when interacting with the screen and fast response would be nice, make dedicated polls just for the functionality needing instant update. The user usually doesn't sit and look at the display for the entire period of charging, the screen could be dimmed (or even turned off) after some touch timeout, poll less often in such situation.

The display wouldn't be actually the most important functionality, it's the ESP inside of it...