Problems with TFT color display with Teensy 4

[Indy]

Hello all,

I've been playing with the Teensy 4 (T4) for awhile with no issues and recently I picked up the color TFT display from PJRC to use with it. Although I have a lot of experience with electronics and microcontrollers (mainly ATmega based) this is the first time I've used a TFT display and SPI communications.

So, my problem is that I cannot get the TFT display to consistently work. For example, I built the 1st circuit on a breadboard - worked fine with no problems. 2nd circuit, display doesn't work at all (white screen). I built a harness for the display, worked fine with no issues. Built a second identical harness, doesn't work (white screen). Had some PCBs made - one worked fine, others wouldn't work at all (white screen). Never say never, but I've went thru so many iterations of building and rebuilding these circuits I'm 99.9% sure it is not an issue of wiring the displays.

On the last PCB I tried I noticed if my finger was on one end of the display PCB the screen would operate correctly on power-up, once I took my finger off it would go white screen. The end I was touching was Vcc, Gnd, CS, RESET, DC... This is consistently repeatable (also with a different display).

I have tried a different Teensy and a different display - the good circuits worked, the 'bad' circuits don't. I found a few mentions of ground bounce and tried to beef up the ground connections - didn't help. I found the thread on this forum suggesting using 10K pull-up resistor for CS and DC - didn't help.

Sorry for the length. Any help would be appreciated.

Thank you,
David

 

[leacolumbi]

Hey, it seems we are on a boat quite alike, only you've got a lot of experience, mine I thought was something, but recently been doubting about it...

the thread https://forum.pjrc.com/threads/64006-What-type-of-cable-to-use might have some things on the side of the cables, if you are connecting through long cables... also, from what I've found, having more than one SPI connection might rise the need of lowering the inductance...

hope it is of any help

 

[japreja]

I have this same issue on occasion, although a different manufacture of display, it has the same chips. I know it is not my wiring, breadboard, teensy, or code. I believe it may be that the display is not powering up fully in time for the teensy. Try making sure that 3v3 is applied to the display first, then powerup the teensy. Or try a 1 second delay as the very first line of the setup() function. If that solves it, then you will need to ensure that the display gets powered up first.

 

[Indy]

leacolumbi & japreja - thank you for your replies. In my case the instability was self-inflicted, I had wired the touch display SPI pins for future use but left a few pins floating. This caused the random problems.

After that I still had a few issues but changing to the ILI9341_t3 library (from the Adafruit ILI9341 library) and putting a small delay between the touch initialization and display initialization has seemed to resolve all my issues.

Thanks again.