Saturday, June 16, 2018

A touch numeric keyboard for Arduino or Teensy

 A system for entering numerical values in our programs on Arduino or Teensy is described. To test this function I wrote also a simple analog data logger program.

The touchscreen keyboard

Very often, for our programs, we need a system to set parameters, usually of a numerical type. A 4x4 keyboard requires some space and then we also need a display. Here is the idea of using a touchscreen display to do both.
I have then written the GetNum function that allows you to print a prompt message and to type an integer number.
To test this function I wrote a simple analog data logger program that required two parameters, the first is the sampling period and the second the number of samples. In this example the number of channels to be scanned is set to three, but the program can be modified to request a third parameter with the number of channels.
As hardware a 2.8" TFT touch shield for Arduino with resistive touch screen can be used.  On the market there are many types, you only need to use the libraries suitable for the controllers that are mounted on the shield.
To test the prototype I used a 3.2" touch screen interfaced to a Teensy LC board. In my case, I had to do a lot more soldering work, but I like it and it is creative too. For more details of my display refer to the post "Adapt a 3.2" TFT display for Raspberry to Arduino ", in my blog ArduPicLab.

The touch keyboard graphics
For the numeric keyboard I used 12 keys, arranged on 3 rows and 4 columns according to the following figure.
In addition to the numeric keys, I added the "C" key to delete the set number and the "ok" key to accept it. The upper space is occupied by the printing of the number to be set and the prompt message that tells the operator what is required by the program. The numbers on the keys are written in tft.setTextSize (3) while the prompt message is written in tft.setTextSize (2) and has a maximum of 19 characters in length. The message is printed in yellow on a black background while the number to be set is printed in black on a cyan background tft.setTextSize (4). The previous figure shows the appearance of an example that requires sampling time in [ms] and 250 was keyed.

The touchscreen calibration
This operation is necessary to know the coordinates of the vertices of the keyboard for which it is necessary to write a simple program that prints the coordinates of the contact points on the display. . To do this I made a program that traces the keyboard on the screen and prints the x, y coordinates on the top. With the stylet I pressed on the grid of the keyboard and I wrote the coordinates on a sheet and then I averaged the values by row and by column. The results are shown in the following figure.
These numbers are indispensable for identifying keys with the DetectButtons () function. It proceeds by column, starting from the left. For each column, examine the rows starting from the lowest. Using other displays the numbers could be very different from those I obtained, so it is important to calibrate the touch screen.

The GetNum function
This function has the following syntax:
unsigned int GetNum (String prompt)
The prompt string is passed from the calling program. The routine turns black the screen, prints the prompt, draws the keys and waits in loop for the required number to be keyed. By pressing the "ok" button the data is returned to the program.
This function accepts unsigned integers from 0 to 65535, but with some minor changes it can work with larger numbers. Things get complicated with numbers with decimals: one more key is needed.

The hardware
As I said, if you buy the shield for Arduino you do not have to do any work because everything is ready, but in my case I had to work a lot.
The graphics resolution of this display is good, QVGA means ¼ of VGA, ie half the pixels on each side, so 240x320 points with 64K or 256K colors. Many shields have the ILI9340 chip as a graphic controller and the XPT2046 as a touch screen controller. The interface used is SPI. The shields for Arduino also have a SD card connector on the back, very convenient for loading images or saving data.
But the card for Raspberry I used did not have the micro SD connector and I had to add it.
The electrical scheme of my prototype is that of the following figure. If I had used a shield for Arduino, things would have been much simpler, I should not have used the solder.

I expected to have three analog channels, so I used a 5-pin connector also to power any sensors.
The button key0 I have dedicated to duplicate the "program" button that is no longer accessible because below the display.
Unlike Arduino Uno, Teensy has a 12-bit converter. The following figure shows the board of my prototype.

The datalogger program
I used the Adafruit libraries. As an example of using the GetNum function, I wrote a program to acquire three analog signals, converted with 12-bit ADC (10 bits for Arduino Uno ADC), and transfer them to the micro SD card. The program asks for the sampling period in [ms], checking the number, then asking for the number of samples.
Then it makes the acquisition, also printing the data on the screen for long times. The file name is always the same, and new acquisitions are added in the queue.
Of course you can improve by asking for other parameters, such as the number of channels or the file number.

TeensyTFTacq and uSD test program
based on Adaftuit TFT library
Giovanni Carrera, rev 15/06/2018

#include "SPI.h"
#include <SD.h>
#include "Adafruit_GFX.h"
#include "Adafruit_ILI9340.h"
#include <XPT2046_Touchscreen.h>

#if defined(__SAM3X8E__)
    #undef __FlashStringHelper::F(string_literal)
    #define F(string_literal) string_literal

// These are the pins used for the TeensyTFT32
#define _sclk 13
#define _miso 12
#define _mosi 11
#define _cs 10
#define _dc 7
#define _rst 8
// for TeensyTFT32 touchscreen
#define CS_PIN  4
#define TIRQ_PIN  3
// for TeensyTFT32 uSD card
const int chipSelect = 9;

unsigned long startMillis, ns;
unsigned long deltat = 200;// period in ms
unsigned int value,NSamples;
boolean SDok = false;
int X,Y;
long Number;
boolean ok = false;

File logFile;

XPT2046_Touchscreen ts(CS_PIN, TIRQ_PIN);// interrupt enabled polling

//Adafruit_ILI9340 tft = Adafruit_ILI9340(_cs, _dc, _mosi, _sclk, _rst, _miso);
// Use hardware SPI
Adafruit_ILI9340 tft = Adafruit_ILI9340(_cs, _dc, _rst);

void setup() {
  tft.begin();// initialize ILI9340
  ts.begin();// initialize XPT2046_Touchscreen
  tft.setCursor(0, 100);
  tft.setTextColor(ILI9340_GREEN); tft.setTextSize(2);
  tft.println("TeensyTFT32 logger");
  tft.println("Initializing SD");
  // check if the SD is present and functioning
  if (!SD.begin(chipSelect)) {
    tft.println("Bad or absent SD");
    // does not do anything else
  tft.println("Card initialized");
  ns= 0;
  value = GetNum("Sample Period [ms]=");
  if (ok){
    if (value==0) value = 1;// minimum value 1ms
    deltat= value;
    ok= false;
  value = GetNum("Number of samples=");
  if (ok){
    if (value==0) value = 1;// minimum value 1
    NSamples= value;
    ok= false;
  String dataString = "Sample Period = "+String(deltat)+" [ms]";
  logFile ="datalog.txt", FILE_WRITE);
  tft.setRotation(1);// 90°
  tft.setCursor(0, 100);
  tft.setTextColor(ILI9340_GREEN); tft.setTextSize(2);
  dataString = "Number of samples = "+String(NSamples);
  logFile.println(", " + dataString);
  SDok = true;

void loop(void) {
  startMillis = millis();
  while( millis() - startMillis < deltat);// loop for deltat msec
  String dataString = String(ns)+ ", ";
  int val;
  for (int i=0; i <= 2; i++){
    val = analogRead(i);
    val = map(val,0,4095,0,3299);// convert values in mV
    dataString += String(val);
    if (i < 2) dataString += ", ";
  if (deltat >= 500){ // print only for long periods
    tft.fillRect(0, 0, 479,70, ILI9340_BLACK);// clear previous prints
    tft.setCursor(0, 0);
    tft.setTextColor(ILI9340_YELLOW); tft.setTextSize(2);
  if (SDok){
    logFile.println(dataString);// save nsample,A0,A1,A2
    if (ns== NSamples){
      SDok= false;// stop acquisition
      tft.setCursor(20, 200);
      tft.setTextColor(ILI9340_BLUE); tft.setTextSize(2);
      tft.println("End of acquisition");

// Functions used
unsigned int GetNum(String prompt){
// print a numeric keyboard and a prompt message
// and get a numeric unsigned integer
 draw_BoxNButtons();// draw the virtual keyboard
 tft.setCursor(10, 20);
 tft.println(prompt); //print prompt
 do { // repeat until ok is pressed
  if (ts.touched()) {
    TS_Point p = ts.getPoint();
    X= p.y; Y= p.x;// invert the axes
 }while (!ok);
 return Number;

void draw_BoxNButtons() {
  String symbol[3][4] = {
    { "6", "7", "8", "9" },
    { "2", "3", "4", "5" },
    { "C", "0", "1", "ok" }
  //Draw the Result Box
  tft.fillRect(0, 60, 240, 80,ILI9340_CYAN);

 //Draw keys
  tft.fillRect  (0,260,60,60,ILI9340_RED);
  tft.fillRect  (0,140,240,120,ILI9340_BLUE);
  tft.fillRect  (60,260,120,60,ILI9340_BLUE);
  tft.fillRect  (180,260,60,60,ILI9340_GREEN);

  //Draw Horizontal Lines
  for (int h=140; h<=320; h+=60)
  tft.drawFastHLine(0, h, 240,ILI9340_WHITE);

  //Draw Vertical Lines
  for (int v=0; v<=240; v+=60)
  tft.drawFastVLine(v, 140, 1800,ILI9340_WHITE);

  //Display keypad lables
  for (int j=0;j<3;j++) {
    for (int i=0;i<4;i++) {
      tft.setCursor(22 + (60*i), 160 + (60*j));
      if (j==2 & i==3) tft.setTextColor(ILI9340_BLACK);// ok is more visible

void DetectButtons(){
  int TSx[] = {319,1174,2097,3031,3838 };// Touch Screen x intervals
  int TSy[] = {1764,2445,3124,3752};// Touch Screen y intervals
  if (X<TSx[1] && X>TSx[0]){ //detecting Buttons on Column 1
    if (Y>TSy[2] && Y<TSy[3]) Number= 0;//If Cancel button is pressed
    if (Y>TSy[1] && Y<TSy[2]) Number= (Number*10)+2;// button 2 is pressed
    if (Y>TSy[0] && Y<TSy[1]) Number= (Number*10)+6;// button 6 is pressed
  if (X<TSx[2] && X>TSx[1]){ //detecting buttons on Column 2
    if (Y>TSy[2] && Y<TSy[3]) Number= (Number*10)+0;// button 0 is pressed
    if (Y>TSy[1] && Y<TSy[2]) Number= (Number*10)+3;// button 3 is pressed
    if (Y>TSy[0] && Y<TSy[1]) Number= (Number*10)+7;// button 7 is pressed
  if (X<TSx[3] && X>TSx[2]){ //detecting Buttons on Column 3
    if (Y>TSy[2] && Y<TSy[3]) Number= (Number*10)+1;// button 1 is pressed
    if (Y>TSy[1] && Y<TSy[2]) Number= (Number*10)+4;// button 4 is pressed
    if (Y>TSy[0] && Y<TSy[1]) Number= (Number*10)+8;// button 8 is pressed
  if (X<TSx[4] && X>TSx[3]){ //Detecting Buttons on Column 4
    if (Y>TSy[2] && Y<TSy[3]) ok = true;// button ok is pressed  
    if (Y>TSy[1] && Y<TSy[2]) Number= (Number*10)+5;// button 5 is pressed
    if (Y>TSy[0] && Y<TSy[1]) Number= (Number*10)+9;// button 9 is pressed
  tft.fillRect(0, 60, 240, 80, ILI9340_CYAN);  //clear result box
  tft.setCursor(10, 80);
  tft.println(Number); //update new value

3)      “Arduino Touch Screen Calculator using TFT LCD”,  B.Aswinth Raj,

4)      “How to use the TFT display 2.2" QVGA with Arduino”, G. Carrera,


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