TFT Touch Shield V1.0

2.8" TFT Touch Shield is an Arduino / Arduino Mega compatible multicolored TFT display with a 4-wire resistive touch screen. It includes an Arduino shield compatible footprint for attachment. The TFT driver is based on professional Driver IC and with 8 bit data and 4 bit control interface.

Features

Arduino/Seeeduino, Arduino Mega, and Seeeduino Mega compatible

2.8” Size QVGA Display

Resistive Touch Screen

Specification

Item	Min	Typical	Max	Unit
Voltage	4.5	5	5.5	VDC
Current	/	/	250	mA
LCD Panel Size	2.8			inch
View angle	60~120			Deg
Resolution	320x240			/
LCD color	65k			/
Backlight Type	LED			/
LCD driver IC	ST7781R			/
Interface Type	Parallel port ( 8bit Data + 4bit Control )			/
Touch Screen	4-Wire resistive touch screen			/
Active area	43.2*57.3			mm
ESD contact discharge	±4			KV
ESD air discharge	±8			KV
Dimension	72.5x54.7x18			mm
Weight	24±2			g

Cautions

Do not subject the module to mechanical shock or impact by dropping it.

Do not apply excessive force to the display surface or the adjoining areas since this may cause the color tone to vary.

Pins usage on Arduino

D0 - Unused.
D1 - Unused.
D2 - LCD data bit 8.
D3 - LCD data bit 9.
D4 - LCD data bit 10.
D5 - LCD data bit 11.
D6 - LCD data bit 12.
D7 - LCD data bit 13.
D8 - LCD data bit 14.
D9 - LCD data bit 15.
D10 - LCD CS pin, active low.
D11 - LCD RS pin.
D12 - LCD WR pin.
D13 - LCD RD pin.

D14(A0) - Touch Screen Y-.
D15(A1) - Touch Screen X-.
D16(A2) - Touch Screen Y+.
D17(A3) - Touch Screen X+.
D18(A4) - Unused.
D19(A5) - Unused.

Usage

Hardware Installation

Insert the TFT Touch Shield to Seeeduino as shown below.

TFT Programming

The TFT library provides the following Application Programming Interfaces(API). The library makes use of direct access to PORT registers instead of Arduino APIs. This is to increase the speed of communication between MCU and TFT. At present, the library supports Arduino, Arduino Mega (1280 or 2560) and Seeeduino ADK Main Board compatible boards. In Mega the 8bit data port of TFT is distributed to different pins belonging to different ports. This decreases the speed of graphics drawing when compared to Arduino. The choice of port pins are purely based on Arduino / Mega port pin arrangement.

General Functions

setXY(unsigned int poX, unsigned int poY)

Sets the cursor position to (poX,poY). This function is internally used by other graphics APIs.

setPixel(unsigned int poX, unsigned int poY,unsigned int color)

Sets the (poX,poY) pixel to color color. This function is internally used by other graphics APIs.

Lines

drawLine(unsigned int x0,unsigned int y0,unsigned int x1,unsigned int y1,unsigned int color)

Draws a line from pixel (x0,y0) to pixel (x1,y1) with color color.

drawVerticalLine(unsigned int poX, unsigned int poY,unsigned int length,unsigned int color)

Draws a Horizontal Line of length length with color color starting from pixel (poX,poY).

drawHorizontalLine(unsigned int poX, unsigned int poY,unsigned int length,unsigned int color)

Draws a Vertical Line of length length with color color starting from pixel (poX,poY).

Rectangle

drawRectangle(unsigned int poX, unsigned int poY, unsigned int length,unsigned int width,unsigned int color)

Draws a rectangle starting from (poX,poY) of length length, width width and color color.

fillRectangle(unsigned int poX, unsigned int poY, unsigned int length, unsigned int width, unsigned int color)

Draws a filled rectangle starting from pixel (poX,poY) of length length, width width and color color.

Circle

drawCircle(int poX, int poY, int r,unsigned int color)

Draws a circle at (poX,poY) of radius radius and color color.

fillCircle(int poX, int poY, int r,unsigned int color)

Draws a filled circle at (poX,poY) of radius radius and color color.

Text

drawChar(unsigned char ascii,unsigned int poX, unsigned int poY,unsigned int size, unsigned int fgcolor)

Draws a character starting from (poX,poY) using inbuilt font of size size and with color fgcolor. This function is used by drawString() function.

drawString(char *string,unsigned int poX, unsigned int poY,unsigned int size,unsigned int fgcolor)

Draws a string of text starting from (poX,poY) using inbuilt font of size size and with color fgcolor.

TouchScreen Programming

TFT Touch Shield uses the Adafruit Touch Screen Library. To understand the principle behind resistive touch screen refer External Links. In short, a 4-wire resistive touch screen provides two voltage divider each for X and Y axis. By applying proper voltages for each axis and scanning the ADC values the position of the touch can be detected. These values are always prone to noise. Hence a digital filter is used.

To use the TouchScreen Library first create a TouchScreen object by

TouchScreen ts = TouchScreen(XP, YP, XM, YM, 300);

Where XP, YP, XM and YM are ADC port pins connected to XPlus, YPlus, XMinus and YMinus pins of Touch Screen. 300 is the resistance across X plates.

Read the Raw ADC value using

Point p = ts.getPoint();

The Raw ADC value has to be converted to Pixel Co-ordinates. This is done with map function. This mapping changes for v0.9 and v1.0. The demo applications already takes care of this mapping.

p.x = map(p.x, TS_MINX, TS_MAXX, 240, 0); p.y = map(p.y, TS_MINY, TS_MAXY, 320, 0);

The following sketch demonstrates use of TouchScreen Library. This can also be used to calibrate the touch screen co-ordinates.
Compile and upload the sketch.
Open serial port monitor and touch the points displayed on the screen.
See if the displayed X and Y values are correct. If not, we have to re-calibrate the touch screen coordinates.

How to calibrate the touch screen ?

- The parameters TS_MINX, TS_MAXX, TS_MINY and TS_MAXY actually decides the extreme ends of the touch screen and actually forms the calibration parameters.
- The values assigned to these variables are measured ADC values (i.e Raw X, Raw Y) when we touch the extreme diagonal ends of touch screen.
- Touch points (0,0) and (239,319) and note down Raw X and Raw Y values. For better accuracy, try out many times and find the right value.
  - TS_MINX corresponds to ADC value when X = 0 ;
  - TS_MINY corresponds to ADC value when Y = 0 ;
  - TS_MAXX corresponds to ADC value when X = 240 -1 i.e 239 ;
  - TS_MAXY corresponds to ADC value when Y = 320 -1 i.e 319 ;
- Change these parameters in the sketch, recompile and upload to Arduino.
- Repeat the above steps if you still do not get accurate values.

Touch Screen Demo Sketch

#include <stdint.h>
#include <TouchScreen.h>
#include <TFT.h>
 
//Measured ADC values for (0,0) and (240-1,320-1)
//TS_MINX corresponds to ADC value when X = 0
//TS_MINY corresponds to ADC value when Y = 0
//TS_MAXX corresponds to ADC value when X = 240 -1
//TS_MAXY corresponds to ADC value when Y = 320 -1
 
static unsigned int TS_MINX, TS_MAXX, TS_MINY, TS_MAXY;
 
//Touch Screen Co-ordinate mapping register
static unsigned int MapX1, MapX2, MapY1, MapY2;
 
// For better pressure precision, we need to know the resistance
// between X+ and X- Use any multimeter to read it
// The 2.8" TFT Touch shield has 300 ohms across the X plate
 
/* Usage: TouchScreen ts = TouchScreen(XP, YP, XM, YM, 300); 
 Where, XP = X plus, YP = Y plus, XM = X minus and YM = Y minus */
//init TouchScreen port pins. This would be reinitialized in setup() based on the hardware detected.
TouchScreen ts = TouchScreen(17, A2, A1, 14, 300); 
 
void setup(void) 
{
  Tft.init();//init TFT
  initTouchScreenParameters(); //initializes Touch Screen parameters based on the detected TFT Touch Schield hardware
 
  //Lines
  Tft.drawLine(0,0,50,50,RED);//draw a 45degree red line point(0,0) to point(50,50) 
  Tft.drawVerticalLine(25,0,50,GREEN);//draw a vertical green line point(25,0) to point(25,50)
  Tft.drawHorizontalLine(0,25,50,BLUE);//draw a horizontal blue line point(0,25) to point(50,25)
 
  //Rectangle
  Tft.drawRectangle(50,0,80,50,WHITE);//draw a white rectangle, length=80(X-AXIS), width=50(Y-AXIS)
  Tft.fillRectangle(0,50,50,80,CYAN);//fill a cyan rectangle, length=50(X-AXIS), width=80(Y-AXIS)
 
  //Circle
  Tft.drawCircle(75,75,25,RED);//draw a red circle, circle centre(75,75) radius=25
  Tft.fillCircle(150,100,50,GREEN);//fill a green circle, circle centre(150,100) radius=50
 
  //Text
  Tft.drawChar('S',0,150,2,RED);//draw a char, start from point(0,150) font size 2(16*16)
  Tft.drawString("Seeed Studio",8,166,2,GREEN);//draw a char, start from point(8,166) font size 2(16*16)
}
 
void loop(void) 
{
  // a point object holds x y and z coordinates
  Point p = ts.getPoint();
 
  p.x = map(p.x, TS_MINX, TS_MAXX, MapX1, MapX2);
  p.y = map(p.y, TS_MINY, TS_MAXY, MapY1, MapY2);
 
  // we have some minimum pressure we consider 'valid'
  // pressure of 0 means no pressing!
  if (p.z > ts.pressureThreshhold) 
  {
    //p.x;
    //p.y;
    //p.z;
    Tft.fillCircle(p.x,p.y,2,GREEN);
  }
}
 
void initTouchScreenParameters()
{
  //This function initializes Touch Screen parameters based on the detected TFT Touch Schield hardware
 
  if(Tft.IC_CODE == 0x5408) //SPFD5408A TFT driver based Touchscreen hardware detected
  {
#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
    ts = TouchScreen(54, A1, A2, 57, 300); //init TouchScreen port pins
#else 
    ts = TouchScreen(14, A1, A2, 17, 300); //init TouchScreen port pins
#endif
    //Touchscreen parameters for this hardware
    TS_MINX = 120;
    TS_MAXX = 910;
    TS_MINY = 120;
    TS_MAXY = 950;
 
    MapX1 = 239;
    MapX2 = 0;
    MapY1 = 0;
    MapY2 = 319;
  }
  else //ST7781R TFT driver based Touchscreen hardware detected
  {
#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
    ts = TouchScreen(57, A2, A1, 54, 300); //init TouchScreen port pins
#else 
    ts = TouchScreen(17, A2, A1, 14, 300); //init TouchScreen port pins
#endif 
 
    //Touchscreen parameters for this hardware
    TS_MINX = 140;
    TS_MAXX = 900;
    TS_MINY = 120;
    TS_MAXY = 940;
 
    MapX1 = 239;
    MapX2 = 0;
    MapY1 = 319;
    MapY2 = 0;
  }
}

Demo Code shown

Insert the TFT Touch Shield to Seeeduino as shown below.

TFT Touch Shield connected to Seeeduino

Version Tracker

Revision	Descriptions	Release
v1.1	change pictures and demo code combination	22 November 2011
v1.0	Use of SPFD5408A based TFT instead of ST7781R driver chip based TFT	12 September 2011
v0.9b	Initial public release	24th June 2011

Support

Ask questions on Seeed forum.

Resources

How to buy

Click here to buy: 2.8 TFT Touch Shield

Licensing

This documentation is licensed under the Creative Commons Attribution-ShareAlike License 3.0 Source code and libraries are licensed under various Open Source licenses. See source code files for details.

External Links

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