ILI9486 TFT touch screen caused unexpected circuit behavior

Hi,
I have some circuit connected to some distances sensors and buttons on an Ardiono mega.
now once I connect ILI9486 touch screen , the same circuit starts behaving weirdly - things like limit switch is detected as closed even when it is not.

Also, when I try to upload some LCD test sketch on the screen - it works when only the screen is connected, but when I connect also my circuit in addition to the screen, the screen's test code doesn't work (I see while screen only).

Any idea what might be causing this ? are there any limitations I should be aware with when working with both screen and other electronic circuit on the same board?

Post a schematic of your problem project and the full code you are using. Without them it is difficult to provide help

The easier you make it to read and copy your code the more likely it is that you will get help

Please follow the advice given in the link below when posting code , use code tags and post the code here

If you get errors when compiling please copy them from the IDE using the "Copy error messages" button and paste the clipboard here in code tags

  1. Please post link to the actual display e.g. Ebay sale page
  2. Install library(s) via the IDE Library Manager
  3. Run all the library examples.

This verifies that your display is working ok.

Only then do you try writing custom programs.

  1. paste / attach your custom program
  2. post schematic of your wiring and external electronics

As UKHeliBob has suggested, "make it easy" and you get the "best" help.

David.

  1. Please post link to the actual display e.g. Ebay sale page
    This is the link of the doc from the website I purchases the screen from https://www.4project.co.il/documents/doc_6779_5806.pdf

  2. Install library(s) via the IDE Library Manager

  3. Run all the library examples.
    This verifies that your display is working ok.
    Display is working just fine, touch calibration etc, I even wrote a small codec of mine and verified it on a Arduino uno board looks good.

Only then do you try writing custom programs.

  1. paste / attach your custom program
  2. post schematic of your wiring and external electronics

As UKHeliBob has suggested, "make it easy" and you get the "best" help.
I see, I dont have schematic, 26 digital pins from D22-D53 are being used:
11 input: 3 x buttons , 2 x limit switches, 3 x SR04 echo, 3 x DS18B20 temperature sensors input
15 output: 3 x SR04 trigger, 8 x relay, 4 x for L298N to drive 2 dc motors

Foad

Draw one with pencil and paper. Photograph it and upload it here

Post your code as requested

Your PDF document does not have any photos of the pcb.
The title says "3.5inch TFT Touch Shield" which implies that it is a "shield" that should "plug into" Arduino header sockets.

Is it the same item as https://www.waveshare.com/wiki/3.5inch_TFT_Touch_Shield ?

We need to know which pins are used for external electronics.
I would expect 50-52 to be used by the Shield's SPI interface.

David.

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