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	5 V	5V
3	BCM 2 (SDA)		4	5 V	5V
5	BCM 3 (SCL)		6	Gnd	Gnd
7	BCM 4 (GPCLK0)	P7	8	BCM 14 (TXD)
9	Gnd	Gnd	10	BCM 15 (RXD)
11	BCM 17	P0 - TP IRQ	12	BCM 18 (PWM0)	P1 – Key0
13	BCM 27	P2 - RST	14	Gnd	Gnd
15	BCM 22	P3 - DC	16	BCM 23	P4 – Key1
17	3.3 V	3.3V	18	BCM 24	P5 – Key2
19	BCM 10 (MOSI)	P MOSI	20	Gnd	Gnd
21	BCM 9 (MISO)	P MISO	22	BCM 25	P6
23	BCM 11 (SCLK)	P SCK	24	BCM 8 (CE0)	P CE0
25	Gnd	Gnd	26	BCM 7 (CE1)	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

1)      https://www.waveshare.com/3.2inch-rpi-lcd-b.htm

2)      https://www.waveshare.com/product/arduino/shields/wavesharer/3.2inch-tft-touch-shield.htm

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