How to Connect a Raspberry PI Touchscreen Display

The new official Raspberry PI touchscreen 7 inch display is now available and connects directly to a Raspberry PI board using a flat ribbon cable and power wires that are supplied with the display.

Raspberry PI Touchscreen Display Running Raspbian

Raspberry PI Touchscreen Display Running Raspbian









Touchscreen Power

The screen operates from a 5V supply and can be powered from the Raspberry PI header pins using the supplied wires. The screen can also be powered from its own external 5V power supply and has a micro USB connector identical to the one used to supply power to Raspberry PI boards. If a separate power supply is used to power the screen, it must be rated at 500mA or more.

Mounting a Raspberry PI Board on the Touchscreen

Terminal posts are provided at the back of the touchscreen that hold the touchscreen circuit board in place. A raspberry PI board can be mounted on the back of the touchscreen by attaching it with the four screws that are supplied with the screen to the terminal posts.

The image below shows a Raspberry PI 2 model B attached to the back of a Raspberry PI touchscreen.

Raspberry PI Board Mounted on Raspberry PI Touchscreen

Raspberry PI Board Mounted on the Back of the Touchscreen

Connecting a Raspberry PI to the Raspberry PI Touchscreen

It is important to make the connections between the Raspberry PI board and touchscreen correctly, especially the power to the screen when it is tapped from the header of the Raspberry PI board.

A flat ribbon cable is supplied with the screen for making a data connection between the raspberry PI board and screen. Jumper wires are supplied with the board for connecting 5V and GND from the Raspberry PI header pins to the touchscreen to supply power to the screen.

Full connection details including photos and a video can be found in the article on how to connect the official 7″ LCD Raspberry PI touchscreen to a Raspberry PI board.

Raspberry PI Touchscreen Connections

Raspberry PI Touchscreen Connections


Arduino Uno Interfacing GT-511C3 Fingerprint Scanner Demo Software

ADH Technology, the company that sells the GT-511C3 fingerprint scanner provide SDK software that includes a demo application for running on a PC. The demo software allows the scanner to be used to enrol fingerprints, each with a unique ID and then identify enrolled fingerprints when a finger is placed on the scanner later. The GT-511C3 fingerprint scanner demo software also includes several other functions that allow fingerprints to be deleted, display number of registered fingerprints, etc.

A USB to TTL level device is normally needed to connect the fingerprint scanner to a Windows PC to use the demo application.

Connecting the GT-511C3 Fingerprint Scanner to a PC using an Arduino

The article on interfacing the GT-511C3 to a PC running the demo software provides a quick hack that uses an Arduino Uno as a USB to TTL converter. The Arduino Uno uses a software serial port to connect to the fingerprint scanner because the only hardware serial port on the Uno is connected to the USB chip which is used as the interface to the PC USB port.

Serial data is relayed between the fingerprint scanner and demo software on the PC by a sketch running on the Arduino. The image below shows the demo application and interface to the scanner. Also see the full article that explains the hardware connections and software needed for the project.

GT-511C3 Fingerprint Scanner PC Demo Software using Arduino Uno

GT-511C3 Fingerprint Scanner PC Demo Software using Arduino Uno

How to Use Arduino Serial Ports

Arduino boards such as the Uno, MEGA2560 and Due all have a serial port that connects to the USB device port on the board. This port allows sketches to be loaded to the board using a USB cable. Code in a sketch can use the same USB / serial port to communicate with the PC by using the Arduino IDE Serial Monitor window, or a Processing application for example. The USB port appears as a virtual COM port on the PC.

This article shows how to use Arduino serial ports when additional serial ports are needed for a project.

Arduino Serial Ports Available

The serial port for programming the Arduino mentioned above is a hardware serial port. The microcontroller on the Arduino board has a hardware serial port built-in, so that after the port has been initialized by software, a byte sent to the port will be sent out serially by the hardware.

The Arduino Uno has only one hardware serial port because the microcontroller used on the Uno has only one built-in serial port. The Arduino MEGA 2560 and Arduino Due both have 3 extra hardware serial ports.

Serial Port Technical Details

The hardware serial ports referred to here are UART (Universal Asynchronous Receiver Transmitter) ports. They may be referred to as USART (Universal Synchronous Asynchronous Receiver Transmitter) ports in the microcontroller documentation if they are configurable in both synchronous and asynchronous modes.

Arduino Uno Serial Port

This image shows the only serial port available on the Arduino Uno highlighted in red. The port connects through a USB chip to the USB device port.

Arduino Uno Serial Port

Arduino Uno Serial Port

Arduino MEGA 2560 and Due

Both the MEGA 2560 and Due have 4 serial ports in total. One that connects through a USB port chip to the USB device port on the board and three extra serial ports that connect to pins on one of the pin headers of the board.

Arduino Due Serial Ports

Arduino Due Serial Ports


Arduino MEGA 2560 Serial Ports

Arduino MEGA 2560 Serial Ports

Pins 0 and 1 of the Due and MEGA connect serial port 0 through to the USB device port so that these Arduino boards are compatible with the pin numbering of the Uno and therefore with Arduino shields.

The extra serial ports are ports 1 to 3 with each port having a transmit and receive pin.

It is important to be aware that the MEGA 2560 serial port pins use 5V voltage levels, but the Due uses 3.3V voltage levels.

How to Use Additional Arduino Serial Ports

An extra serial port can be used on an Arduino Uno, but must be simulated in software by using the SoftwareSerial library.

Arduino Uno

The following code is taken from the article on serial communications with the GT-511C3 fingerprint scanner which connects the fingerprint scanner to a software serial port on an Arduino Uno.

#include <SoftwareSerial.h>

SoftwareSerial gtSerial(8, 7); // Arduino RX, Arduino TX

void setup() {
  Serial.begin(9600);    // serial / USB port
  gtSerial.begin(9600);  // software serial port

byte rx_byte = 0;        // stores received byte

void loop() {
  // check if byte available from USB port
  if (Serial.available()) {
    rx_byte =;
    // send a byte to the software serial port

  // check if byte available on the software serial port
  if (gtSerial.available()) {
    // get the byte from the software serial port
    rx_byte =;

To use the software serial port, first the header file for the software serial library must be included.

#include <SoftwareSerial.h>

Next create the software serial port, selecting the Arduino pins to use for receive (RX) and transmit (TX). Here pin 8 has been set as the receive pin and pin 7 as the transmit pin.

SoftwareSerial gtSerial(8, 7);

The software serial port had been given the name gtSerial which will be used in the sketch to refer to this serial port.

The port can now be checked for incoming data.

if (gtSerial.available()) {

If data is available, it can be read from the port.

rx_byte =;

Data bytes can also be sent on the port.


How to Use Additional Serial Ports on the Arduino MEGA 2560 and Due

The additional hardware ports on the Arduino MEGA 2560 and Due can be used in the same way as the main USB serial port is used in sketches, only changing the name of the port. The USB serial port, or serial port 0 is referred to as Serial in sketches. To use serial port 1, the name changes to Serial1. Serial ports 2 and 3 are referred to as Serial2 and Serial3.

This sketch shows serial port 3 being used which transmits on pin 14 of the MEGA or Due and receives on pin 15.

void setup() {
  // initialize serial ports
  Serial.begin(9600);    // USB serial port 0
  Serial3.begin(9600);   // serial port 3

byte rx_byte = 0;        // stores received byte

void loop() {
  // check for data byte on USB serial port
  if (Serial.available()) {
    // get byte from USB serial port
    rx_byte =;
    // send byte to serial port 3
  // check for data byte on serial port 3
  if (Serial3.available()) {
    // get a byte from serial port 3
    rx_byte =;
    // send the byte to the USB serial port

The additional serial ports are immediately available in the sketch without having to include any libraries.

Serial port 3 must first be initialized to the desired baud rate.


The port can be checked for incoming data.

if (Serial3.available()) {

If a byte has arrived on the serial port, it can be read.

rx_byte =;

A byte can be written to the serial port.


Arduino Serial Port Resources

Arduino Website References for Software and Hardware

Projects, Articles and Tutorials

Can’t Find Arduino Due in Board List of IDE

Can’t find Arduino Due on the menu and therefore can’t load a sketch to the board? The Arduino Due does not appear in the board list of the Arduino IDE under the tools menu. Boards are normally listed under Tools → Board in the Arduino IDE, but if you can’t find the Arduino Due on the Board menu, additional software must be installed from within the IDE.

The Arduino Due used to have a separate IDE, but was later merged with the main Arduino IDE software. It is now a requirement to install the extra software in order to be able to program the Due.

Can’t Find Arduino Due on the Menu in the Arduino Software

In the image below, the Arduino Due is missing from the menu. The steps below show how to solve the problem and get the Arduino Due board listed on the menu.

Can't find Arduino Due on the menu - Arduino Due missing

Arduino Due Does not Appear in Board List of Menu

Installing Software for the Arduino Due

The following screen captures show how to install the software for the Arduino Due.

1. Boards Manager

Select the Boards Manager menu item from the Arduino IDE menu.
Tools → Board → Boards Manager …

Arduino IDE Boards Manager

Arduino IDE Boards Manager

2. Select Arduino SAM Boards

Click the Arduino SAM Boards item in the Boards Manager dialog box and then click the Install button.

Select Arduino SAM Boards

Select Arduino SAM Boards

It will take some time to install the software, depending on how fast the Internet connection is. After installation, click the Close button in the dialog box.

Programming the Arduino Due

After installation, the Arduino Due board will appear on the Board menu. Select Arduino Due (Programming Port) to allow Arduino sketches to be loaded to the board from the Arduino IDE. The USB cable must be plugged into the USB port labelled PROGRAMMING on the bottom of the board.

Arduino Due Programming Port

Arduino Due Programming Port


HTML Text Box to Send Text to Arduino Web Server

An Arduino and Ethernet shield are used as a web server to host a web page that contains a text box. Text can be typed into the web page text box using a web browser and sent to the Arduino by clicking a button on the web page.

An HTML textarea is used in an HTML form to create the text box. JavaScript is used to send the text to the Arduino using a HTTP GET request when the button on the web page is clicked. This is useful for any Arduino project that needs to receive text from a web page using a text box.

The Arduino code for this project follows the format of the Ajax I/O web server from the Arduino Ethernet shield web server tutorial, except that it calls the JavaScript function that sends the GET request when the button on the web page is clicked rather than periodically sending the GET request to the Arduino web server.

The video below shows the Arduino web page being accessed by a web browser and text being sent to the Arduino.


Arduino Hardware, Software and HTML Page Setup


An Arduino Uno and Arduino Ethernet shield with 2GB micro SD card were used to test the project. Most Arduino boards that are compatible with the Ethernet shield should work.


Copy the HTML from below to a file called index.htm on the micro SD card and insert it into the Ethernet shield micro SD card socket. Load the Arduino sketch from below to the Arduino — first change the MAC and IP address in the sketch to suit your own network. In the Arduino IDE Serial Monitor window, set the baud rate at the bottom of the window to 115200.

Running the Project

With the Arduino connected to the Ethernet network, first open the Serial Monitor window, then open a web browser and surf to the IP address set in the sketch. Text can be typed into the text box on the web page and sent to the Arduino. The Arduino will display the text in the Serial Monitor window if the line of text is not too long (the length is set by buffer arrays in the Arduino code).

Arduino Text Box Sketch

The Arduino text box sketch listing called text_area is shown below. Copy and paste it to the Arduino IDE.

  Program:      text_area

  Description:  Arduino web server that gets text from an HTML
                textarea text box on the hosted web page.
                The web page is stored on the micro SD card.
  Date:         23 June 2015
  Author:       W.A. Smith,

#include <SPI.h>
#include <Ethernet.h>
#include <SD.h>
// size of buffer used to capture HTTP requests
#define REQ_BUF_SZ   90
// size of buffer that stores the incoming string
#define TXT_BUF_SZ   50

// MAC address from Ethernet shield sticker under board
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(192, 168, 0, 20);   // IP address, may need to change depending on network
EthernetServer server(80);       // create a server at port 80
File webFile;                    // the web page file on the SD card
char HTTP_req[REQ_BUF_SZ] = {0}; // buffered HTTP request stored as null terminated string
char req_index = 0;              // index into HTTP_req buffer
char txt_buf[TXT_BUF_SZ] = {0};  // buffer to save text to

void setup()
    // disable Ethernet chip
    pinMode(10, OUTPUT);
    digitalWrite(10, HIGH);
    Serial.begin(115200);       // for debugging
    // initialize SD card
    Serial.println("Initializing SD card...");
    if (!SD.begin(4)) {
        Serial.println("ERROR - SD card initialization failed!");
        return;    // init failed
    Serial.println("SUCCESS - SD card initialized.");
    // check for index.htm file
    if (!SD.exists("index.htm")) {
        Serial.println("ERROR - Can't find index.htm file!");
        return;  // can't find index file
    Serial.println("SUCCESS - Found index.htm file.");
    Ethernet.begin(mac, ip);  // initialize Ethernet device
    server.begin();           // start to listen for clients

void loop()
    EthernetClient client = server.available();  // try to get client

    if (client) {  // got client?
        boolean currentLineIsBlank = true;
        while (client.connected()) {
            if (client.available()) {   // client data available to read
                char c =; // read 1 byte (character) from client
                // limit the size of the stored received HTTP request
                // buffer first part of HTTP request in HTTP_req array (string)
                // leave last element in array as 0 to null terminate string (REQ_BUF_SZ - 1)
                if (req_index < (REQ_BUF_SZ - 1)) {
                    HTTP_req[req_index] = c;          // save HTTP request character
                // last line of client request is blank and ends with \n
                // respond to client only after last line received
                if (c == '\n' && currentLineIsBlank) {
                    // send a standard http response header
                    client.println("HTTP/1.1 200 OK");
                    // remainder of header follows below, depending on if
                    // web page or XML page is requested
                    // Ajax request - send XML file
                    if (StrContains(HTTP_req, "ajax_inputs")) {
                        // send rest of HTTP header
                        client.println("Content-Type: text/xml");
                        client.println("Connection: keep-alive");

                        // print the received text to the Serial Monitor window
                        // if received with the incoming HTTP GET string
                        if (GetText(txt_buf, TXT_BUF_SZ)) {
                          Serial.println("\r\nReceived Text:");
                    else {  // web page request
                        // send rest of HTTP header
                        client.println("Content-Type: text/html");
                        client.println("Connection: keep-alive");
                        // send web page
                        webFile ="index.htm");        // open web page file
                        if (webFile) {
                            while(webFile.available()) {
                                client.write(; // send web page to client
                    // reset buffer index and all buffer elements to 0
                    req_index = 0;
                    StrClear(HTTP_req, REQ_BUF_SZ);
                // every line of text received from the client ends with \r\n
                if (c == '\n') {
                    // last character on line of received text
                    // starting new line with next character read
                    currentLineIsBlank = true;
                else if (c != '\r') {
                    // a text character was received from client
                    currentLineIsBlank = false;
            } // end if (client.available())
        } // end while (client.connected())
        delay(1);      // give the web browser time to receive the data
        client.stop(); // close the connection
    } // end if (client)

// extract text from the incoming HTTP GET data string
// returns true only if text was received
// the string must start with "&txt=" and end with "&end"
// if the string is too long for the HTTP_req buffer and
// "&end" is cut off, then the function returns false
boolean GetText(char *txt, int len)
  boolean got_text = false;    // text received flag
  char *str_begin;             // pointer to start of text
  char *str_end;               // pointer to end of text
  int str_len = 0;
  int txt_index = 0;
  // get pointer to the beginning of the text
  str_begin = strstr(HTTP_req, "&txt=");
  if (str_begin != NULL) {
    str_begin = strstr(str_begin, "=");  // skip to the =
    str_begin += 1;                      // skip over the =
    str_end = strstr(str_begin, "&end");
    if (str_end != NULL) {
      str_end[0] = 0;  // terminate the string
      str_len = strlen(str_begin);

      // copy the string to the txt buffer and replace %20 with space ' '
      for (int i = 0; i < str_len; i++) {
        if (str_begin[i] != '%') {
          if (str_begin[i] == 0) {
            // end of string
          else {
            txt[txt_index++] = str_begin[i];
            if (txt_index >= (len - 1)) {
              // keep the output string within bounds
        else {
          // replace %20 with a space
          if ((str_begin[i + 1] == '2') && (str_begin[i + 2] == '0')) {
            txt[txt_index++] = ' ';
            i += 2;
            if (txt_index >= (len - 1)) {
              // keep the output string within bounds
      // terminate the string
      txt[txt_index] = 0;
      got_text = true;

  return got_text;

// sets every element of str to 0 (clears array)
void StrClear(char *str, char length)
    for (int i = 0; i < length; i++) {
        str[i] = 0;

// searches for the string sfind in the string str
// returns 1 if string found
// returns 0 if string not found
char StrContains(char *str, char *sfind)
    char found = 0;
    char index = 0;
    char len;

    len = strlen(str);
    if (strlen(sfind) > len) {
        return 0;
    while (index < len) {
        if (str[index] == sfind[found]) {
            if (strlen(sfind) == found) {
                return 1;
        else {
            found = 0;

    return 0;

Text Box HTML Page

Copy the HTML below and save it to a file called index.htm on the SD card.

<!DOCTYPE html>
<html lang="en">
        <meta charset="utf-8">
        <title>Text Box using textarea</title>

        strText = "";
        function SendText()
            nocache = "&nocache=" + Math.random() * 1000000;
            var request = new XMLHttpRequest();
            strText = "&txt=" + document.getElementById("txt_form").form_text.value + "&end=end";
  "GET", "ajax_inputs" + strText + nocache, true);

    <body onload="GetArduinoIO()">
        <form id="txt_form" name="frmText">
            <textarea name="form_text" rows="10" cols="40"></textarea>
        <input type="submit" value="Send Text" onclick="SendText()" />


How the Text Box Sketch Works

JavaScript embedded in the web page sends the text from the text box to the Arduino as part of a HTTP GET request when the button on the web page is clicked.

Format of the String

This image shows what the string looks like before it is sent to the Arduino.

HTML Text Box and Text String

HTML Text Box and Text String

The text from the text box is put between &txt= and &end=end before being sent. The Arduino uses this text to find the string in the incoming HTTP GET request.

When the text reaches the Arduino, it has been altered with the spaces in the text changed to %20 as shown in the image below.

String from the Text Box Received by Arduino

String from the Text Box Received by Arduino

The Arduino sketch must change %20 in the text back to spaces.

Processing the String in the Arduino Sketch

The function GetText() is used to get the text box string from the incoming HTTP GET request. The HTTP_req array holds the beginning of the incoming GET request as shown in the above image — starting with GET /ajax_inputs&txt…

The GetText() function first gets a pointer to the beginning of the text box string by searching for &txt= and then terminating the string when it finds &end. A for loop is used to copy the string to the txt array (which is a pointer to the global txt_buf array). While the copying is taking place, the code looks for spaces that are encoded as %20 and changes them into spaces.

Limitations of the Arduino Text Box Sketch

The sketch is limited by the size of the buffer that saves the incoming HTTP GET request as well as the size of the array that stores the string from the text box. These two array buffers have been kept small so that the code will be able to run on an Arduino Uno.

If the string from the text box is too big for the HTTP buffer on the Arduino so that the string is truncated before the terminating &end, then the text will not be displayed in the Serial Monitor window because the GetText() function will return false.

This is just a simple demonstration that uses GET to send text. It would be better to send the text using POST instead and this will be added as a tutorial at a later stage.