Wiring TFT display to Arduino Uno

Appearantly this model tft board is old. I don’t see wiring diagrams for this particular board, but have taken some research and wired up. However, I’m only seeing a white screen when plugged in with TFT Display Text sketch on Arduino Uno. I couldn’t figure out what pins to wire SCL and SDA to.

The fragment of the board that appears in the picture is not really enough to identify it.
However, on a Uno, the I2C pins SCL and SDA are pins A5 and A4 respectively.
What library are you intending to use to drive this display device ?

I have just received a "similar" display from Ebay with a green pcb

It "looks" as if the resistor packs would give some protection from 5V logic. i.e. Uno.
However they have a very low value (330R). I would expect 2k2 for "level protection" series resistors but anything from 1k to 10k should be fine.

I have only tried it with 3.3V logic. The display works fine.

For the TFT, I suggest this wiring:

VCC  .. 5V or 3.3V pin should be ok.
GND  .. 0V pin
SDA  .. digital#11 (MOSI pin)
SCL  .. digital#13 (SCK pin)
DC   .. digital #9
RES  .. digital #8
CS   .. digital #10

e.g. for the Adafruit_ST7735 library examples, your constructor would be:

// Option 1: use any pins but a little slower
//Adafruit_ST7735 tft = Adafruit_ST7735(cs, dc, mosi, sclk, rst);

// Option 2: must use the hardware SPI pins
// (for UNO thats sclk = 13 and sid = 11) and pin 10 must be
// an output. This is much faster - also required if you want
// to use the microSD card (see the image drawing example)
//Adafruit_ST7735 tft = Adafruit_ST7735(cs, dc, rst);
Adafruit_ST7735 tft = Adafruit_ST7735(10, 9, 8);

If you are using a 5V Uno, I suggest that you try it with 1k series resistors first. i.e. for each signal pin.

My display contains an ST7735S controller.


Oops. I'm glad you came in there. From the markings, I assumed this was an I2C capable display as the names SCL and SDA are more usually associated with I2C and not SPI.

No, it has a bidirectional "SPI". Just like many other TFT controllers.

The "data" pin is called SDA. The clock pin is called SCL. Just like I2C but it is a very different beast.
I read the registers and read the GRAM memory just like I do with bigger TFTs.
However, the birectional pin is painful with Atmel processors. e.g. with an AVR I can write with hardware SPI but need to read with software bit-bashing.

The really annoying thing is 5V Arduinos. Virtually all external electronics is designed for 3.3V
Ebay vendors "say" you can connect 5V logic to these displays. Most TFT controllers are not 5V tolerant.