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Wednesday 21 February 2018

Adapt a 3.2 "TFT display for Raspberry to Arduino

By Giovanni Carrera, 21/02/2018

The aim of this project is to interface a 3.2"TFT display designed for Raspberry with Arduino .

Introduction
Some time ago I bought a 3.2 "TFT touch screen for my Raspberry. This display is connected to the Raspberry GPIO via a 26-pin connector and appropriate drivers are required. It worked well but it was too small and not very suitable for my eyesight, so I subsequently purchased a 7"display with an HDMI interface. I did not want to leave it unused and I thought about using it with Arduino. I also noticed that the same manufacturer Waveshare sold an Arduino shield with the same display, equipped with the same graphics controller ILI9340 and the touch screen controller XPT2046. The respective libraries are also available for this shield.
Studying the wiring diagram of the board I got what were the signals and the pins used. The following table shows the names of the Raspberry signals and those used by the TFT display.
pin
Raspberry name
TFT
pin
Raspberry name
TFT
1
3.3 V
3.3V
2
5V
3

4
5V
5

6
Gnd
7
P7
8

9
Gnd
10

11
P0 - TP IRQ
12
P1 – Key0
13
P2 - RST
14
Gnd
15
P3 - DC
16
P4 – Key1
17
3.3V
18
P5 – Key2
19
P MOSI
20
Gnd
21
P MISO
22
P6
23
P SCK
24
P CE0
25
Gnd
26
P CE1
Since I had already built a system with an ATMega328P chip powered at 3.3 V [3], I did the test with that board (see my post “How to use the TFT display 2.2" QVGA with Arduino”).
I also realized that the display only worked if I used pin 25 or 14 as a mass. I powered the 5V display on pin 2 and the ground on pin 25. I powered my system with its battery and everything worked good. The program was that of the oscilloscope.
Some signals are different from those in the following table because those were used in my project, while pin 8 turned on the backlight led of the other display.
Since I have not found on the datasheets if the chip inputs are 5 volt tolerant, I would recommend using Arduino boards with 3.3V I/O, even if the Arduino Waveshare shield is connected to boards like Arduino Uno without level adapters.
TFT pin
name
Arduino pin
Description
2
5V
5V
5V power input
25
GND
GND
Ground
23
P SCK
D13
SPI clock
21
P MISO
D12
SPI data input
19
P MOSI
D11
SPI data output
24
P CE0
D10
LCD chip select
13
P2 - RST
D8
LCD reset
15
P3 - DC
D7
LCD data/command selection
??
TP_BUSY
D6
Touch panel busy
26
P CE1
D4
Touch panel chip select
11
TP IRQ
D3
Touch panel interrupt
12
Key0

button 0
16
Key1

button 1
18
Key2

button 2
With a new project based on Teensy, I could also test the touch screen and everything worked very well. I used the Adafruit libraries that also allow you to rotate the text.

References

3)      “How to use the TFT display 2.2" QVGA with Arduino”, G. Carrera,  http://ardupiclab.blogspot.it/

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