display

Display type

It needs the ILI9341 controller.

2.4 inch is recommended.

2.2 inch

will work, but it will interfere with the relay connector. You will need to use a very low height connector

Also if you want to use the SD card, you will need 4 thin wires to do the connection to the SD header.

2.8 inch will work, but will interfere with all surrounding connectors. Only use, if you do not need these connectors.

Suppliers

Everywhere on the internet. Just type "ILI9341 display 2.4" into the search box. DO NOT use the ones with pins on the long side. These fit only on to an arduino.

Instead, use the ones with pins on the short side. See image below.

Check out ebay, aliexpress etc.

Display and SD 3.3V operation

The ILI9341 LCD on the PCB and the SD work ONLY with 3.3V. The display PCB however is intended to be 5V (arduino Vcc) compatible. Unfortunately the PCB manufacturers cheated a bit.

They included a power converter to 3.3 V, which is fine. However they left away the logic level converters for the LCD and the SD.

For the LCD, they assumed that the LCD is 5V tolerant. This is only partly true. The LCD seems to survive it, but the datasheet does not specify 5V tolerance. So who knows how long this will work.

SD cards are definitely not 5V tolerant. They react with sporadic errors, and some die after a few minutes. That's why the manufacturer SOMETIMES added in series resistors to the logic lines. I've seen these displays with 10k resistors, 1k resistors and no resistors at all. The problem with the resistors is that they degrade the waveform, so data transfer becomes unreliable.

To avoid these problems, I added a logic level converter to 3.3v on the hydrocontrol PCB. However now the series resistors to the SD are in the way. 1k works, but with 10k, data communication fails.

If there are 10k resistors, you will have to remove these 3 resistors close to the SD card slot, and bridge the solder points.