Hello, been lurking here for a while and have found a wealth of information thanks to many contributors.
I am using the Photon, and I have successfully compiled both of these libraries and executed the example (Serial monitor gives me the testing stats) BUT, I am getting no output on the screen so I figure that its a wiring issue
https://github.com/mtnscott/Adafruit_ILI9341 and https://github.com/pkourany/ILI9341_SPI_LCD
https://github.com/pkourany/Adafruit_mfGFX_IDE
Here is my Screen and Design (for pinouts):
(2x13 header) https://learn.adafruit.com/adafruit-pitft-28-inch-resistive-touchscreen-display-raspberry-pi/downloads
I have looked at several of the other threads related to hookup and wiring, but I cant even get the screen to come on when powered up! Probably a stupid rookie mistake, but hoping someone can help me out. Only been working on the photon for a month or so, and today is the first day trying to get this screen working - so I probably have a stupid pin issue, more commonly identified as an ID-10-T error!
Look at the design diagram included above for my TFT Pinout. I did Learn that the square solder is PIN #1 
so I believe I have the correct orientation on the header.
my constructor is as follows: Adafruit_ILI9341 tft = Adafruit_ILI9341(A2, A1, A0);
A0 - rst not hooked up
A1 - TFT DC 3V (22)
A2 - TFT_CS 3V (24)
A3 - SLCK 3V (23)
A4 - MISO (21)
A5 - MOSI 3v (19)
and I have
VIN - 3.3v (17) but have tried 3.3 V (1)
GND - GND (25) but have tried GND (20) and GND(6) as well.
Thanks
Rod
@RodBillett, your wiring looks good EXCEPT for the 3.3v part. The Photon 3.3V regulator can only supply an extra 100ma or so of current which is not enough to power this display. You will need to get an alternate 3.3v supply (1A or more) which can power both the Photon (via 3V3 pin) and the display via PIN 1 (which also supplies the 3.3V on the display according to the schematics).
2 Likes
@peekay123, Got it to work this morning, BUT I had to freelance!
I hooked it up as I interpreted your comment above, but still no illumination. Photon powered on, but back light didn’t even come on. Got out the tester and verified 3.2x volts at the connection wires. So, after the obligatory rookie move of plugging into various pins and awaiting anything to happen, I looked at the diagram again. I decided to just try to just get the back-light to light with 3.3v - nothing. So, noticing the diagram had a 5v input and ground (and my new powersuppply also had that on a separate buss), i disconnected everything and went 5v to pin 2 and gnd to pin 6 - Poof, the screen illuminated white!. With new found enthusiasm I reconnected all of the A1-A5 wires and turned on the photon again - nothing but white screen (even tho serial monitor said it was working).
So, being a rookie, and not afraid to vaporize a $20 photon, I decided to hook up the VIN and gnd from photon to my screen
VIN - 17
GND - 25
It worked perfectly then.
So, Why does it need both power supplies?,
Do I need to swap VIN to a 3v3 on the photon or do I just need the gnd wire?,
and how long till the photon or screen fries because I got things all screwed up?
Rod
@RodBillett, the Photon can be supplied from USB, Vin or 3V3. Vin is USB power through a protection diode (so just under 5v). You can supply your circuit via Vin directly if you have enough USB power - This is what your are effectively doing.
You can also power the Photon directly via Vin with 5V. The Photon has an onboard switch mode regulator to produce the 3.3V that the processor needs. The 3V3 output can be used but it can’t supply a lot of current. The 3V3 pin can also be used to power the Photon using a (good) 3.3v source.
The display most likely uses the same approach with 5V needed for the backlight and it sounds like it has a 3.3v regulator to provide power for its logic.
Glad you got it worked out and I really like your “damn the torpedoes” approach to experimenting. THAT is maker spirit! 
1 Like
@peekay123 Thanks for the assistance, Some more fidgeting around, I dont need the wire from (Photon) VIN to 3.3v on the screen BUT the GND wire is needed. Right now I have the photon hooked up to the USB and the screen hooked up to the 5v supply.I dont know why the gnd to the photon is needed when I have one to the power supply. But it all works.
Now off to figure out how to get the touch (stmpe610) part working.
@RodBillett, the connected grounds are needed to create a common reference for any connections like GPIO. Grounds on power supplies are not “true” grounds (earth) and are not zero volts necessarily when compared to another supply’s ground. Tying them together makes them equal and common to all the connected hardware. 
1 Like