TFT with stripes

Hi every one,
I'm new on Arduino but already got some experience in controllers.

I want to do some tests with a TFT-Display with a ST7735 controller.
Therefore I wanted to use the TFT-library which comes with the Arduino Developement environment.

I'm using the following code (example of TFT / circle()):

#include <SPI.h>
#include <TFT.h>            // Arduino TFT library

#define cs   10
#define dc   9
#define rst  8

TFT screen = TFT(cs, dc, rst);

void setup() {
  // initialize the screen
  screen.begin();

  // make the background black
  screen.background(255,0,0);

  // set the stroke color to white
  screen.stroke(255,255,255);

  // set the fill color to grey
  screen.fill(127,127,127);

  // draw a circle in the center of screen
  screen.circle(screen.width()/2, screen.height()/2, 50);
}

void loop() {

}

I expect a circle in white which is filled black on a red background.

That is also what I see, but unfortunately only if:

  • I unplug the SCL-Line after the scatch has finished.
  • Press the reset-button after the scatch has finisched.
  • set the SCL-Line as input at the end of my scatch.

In all other cases I hardly see the image as it is overlayed with some stripes. (see attached picture)
There is also a kind of shadow around the circle.

It seams the error has something to do with the SCL-Line.

Some more facts:

Ps: I've seen the topics where the advice is to change to a newer version of the IDE. I guess I'm using the latest version.

  • The TFT is supplied with 3.3V (According to the datasheet the lines of the TFT-controller are compatible with 5V and the TFT is not destroyed till now, as I see the correct image as described above.)

ST7735:
7.2 DC characteristic. VDDI max voltage = 3.3V

ST7735R:
7.2 DC characteristic. VDDI max voltage = 3.7V

ST7735S:
7.2 DC characteristic. VDDI max voltage = 3.7V

I doubt if you will believe these values from three different Sitronix datasheets.

Looking at your Ebay link. The SD card has series resistors R2-R4. The LED has series resistor R1.
I can't read the values from the photo. You can read them from the item on your desk.

The TFT logic pins have no series resistors.
It is possible that the TFT module has some overvoltage protection on the flexible ribbon that connects to the reverse side of the pcb.

The Red modules from Ebay do NOT like overvoltage.

David.

Thanks for your David,

I now believe the that I should use 3.3V. I don't know where I find the information about the 5V. I can't find it again. (I hope I didn't destroy the displays till now.)

I'll add some voltage divider with 2 resistors, each. Do you thing that is enough?

Ebay descriptions imply that you can connect directly to 5V Uno. An Ebay description is not always truthful.

Yes, voltage dividers will be fine. Series resistors would probably work too.

The TFT.h library is designed for the ST7735. The methods are not very convenient.
The Adafruit_ST7735 library is easier to use. And any graphics written for Adafruit_GFX is likely to work with all the other third party libraries.

David.