I am using an Adafruit 1947 capacitive TFT touch screen which I mounted on an Uno. I also have a Nano 33 BLE, which is connected to a sensor. I want to control a condition with the touch panel. For that, I coded the Nano to give the output to Serial1. I checked with bare Uno and it was able to communicate well with Nano. But the problem arises when I connect the TFT screen to the Uno. In that case, the Nano still sends the correct values, but the Uno gives the wrong number.
PS: I have connected the two boards as described on How to make two Arduino boards talk to each other |, using resistors. I am turning on both by connecting to my PC. Long story short, Uno receives data fine w/o TFT, but when TFT is installed, it mixes up.