Speeding Up Arduino

This article tells how to overclock Arduino with AtMega328P microcontroller. It is necessary to load new bootloader to Arduino with parallel programmer. Clock speed must be set according the crystal frequency.

I have 22.1184 MHz crystal so I must first edit the Makefile for bootloader. It is located normally in this directory:


Edit correct frequency to this line:

atmega328: AVR_FREQ = 22118400L

Find boards.txt file in the system and change frequency and save.


Next task is to create connection between computer and Arduino. To establish connection you need one parallel port on computer and two resistor in series with the lines.


  • Pin 1 (STROBE), resistor 470 ohm, SCK
  • Pin 2 (D0), resistor 470 ohm, MOSI
  • Pin 11 (BUSY), MISO
  • Pin 16 (INIT), RESET
  • Pin 21 (GND), GND (Any GND will do)

Then open Arduino IDE. Select correct board (Nano in my case) and select Parallel Programmer and finally select “Burn bootloader”. You are ready. Arduino is now running at 22MHz. 🙂 You can program it normally by IDE and can use serial monitor like before.

Simple Four Channel Logic Analyzer/Oscilloscope

This simple program uses four pins of Arduino analog port. On version 0.3 there is about 4ms/division and about 400ms delay between measurements. Also measurements is made only when there is some signal on inputs. Old version 0.1 picture is below.

Version 0.2 image.

Version 0.3 image.

New version 0.3 code.

#include "SPI.h"
#include "Adafruit_GFX.h"
#include "Adafruit_ILI9340.h"

#define _cs 10
#define _dc 9
#define _rst 8

Adafruit_ILI9340 tft = Adafruit_ILI9340(_cs, _dc, _rst);

volatile boolean measure = false;

void pciSetup(byte pin) {
  *digitalPinToPCMSK(pin) |= bit (digitalPinToPCMSKbit(pin));  // enable pin
  PCIFR  |= bit (digitalPinToPCICRbit(pin)); // clear any outstanding interrupt
  PCICR  |= bit (digitalPinToPCICRbit(pin)); // enable interrupt for the group

void setup() {


  tft.drawFastHLine(0,(tft.height()/5)*1, 320, tft.Color565(30,30,30));
  tft.drawFastHLine(0,(tft.height()/5)*2, 320, tft.Color565(30,30,30));
  tft.drawFastHLine(0,(tft.height()/5)*3, 320, tft.Color565(30,30,30));
  tft.drawFastHLine(0,(tft.height()/5)*4, 320, tft.Color565(30,30,30));

int xpos = 0;

  int pin0_state[161];
  int pin1_state[161];
  int pin2_state[161];
  int pin3_state[161];

void loop() { 
  if(!measure) return;
  measure = false;
  unsigned long start = 0;
  unsigned long end_time = 0;


  start = micros();
  for(int i = 0; i < 160; i++) {
    pin0_state[i] = analogRead(0);
    pin1_state[i] = analogRead(1);
    pin2_state[i] = analogRead(2);
    pin3_state[i] = analogRead(3);
  end_time = micros() - start;

  for(int i = 0; i < 320; i=i+2) {
    if(!(i%20)) tft.drawFastVLine(i, 17, tft.height(), tft.Color565(30,30,30));
    else tft.drawFastVLine(i, 17, tft.height(), ILI9340_BLACK);
    tft.drawPixel(i, ((tft.height()/5)*1)-(pin0_state[i/2]/32), ILI9340_YELLOW);
    tft.drawPixel(i, ((tft.height()/5)*2)-(pin1_state[i/2]/32), ILI9340_RED);
    tft.drawPixel(i, ((tft.height()/5)*3)-(pin2_state[i/2]/32), ILI9340_GREEN);
    tft.drawPixel(i, ((tft.height()/5)*4)-(pin3_state[i/2]/32), ILI9340_CYAN);

  tft.setCursor(0, 0);
  tft.fillRect(0, 0, 320, 17, ILI9340_BLACK);
  tft.print((end_time/1000)/16); //one div is X milliseconds
  tft.print("ms/div, int:");
  tft.print((micros() - start)/1000); //interval time

ISR (PCINT1_vect) {
  measure = true;

Here is simple analog datalogger code. Analog value can be between zero and 127. It is viewable with external software.

void setup() {
pinMode(A3, INPUT); 
pinMode(A2, INPUT); 
pinMode(A1, INPUT); 
pinMode(A0, INPUT);


void loop() {

  char testi[101] = {};
  char testi1[101] = {};
  char testi2[101] = {};
  char testi3[101] = {};
  for(byte i=0; i<100; i++) {
    int temp0 = analogRead(0);
    int temp1 = analogRead(1);
    int temp2 = analogRead(2);
    int temp3 = analogRead(3);
    testi[i] = (temp0/8)-1;
    testi1[i] = (temp1/8)-1;
    testi2[i] = (temp2/8)-1;
    testi3[i] = (temp3/8)-1;


Even simpler version that outputs data in CSV format.

void setup() {
pinMode(A3, INPUT);
pinMode(A2, INPUT);
pinMode(A1, INPUT);
pinMode(A0, INPUT);


void loop() {

  char text[101] = {};
  for(byte i = 0; i < 93; i = i + 8) {
    int temp0 = analogRead(0);
    int temp1 = analogRead(1);
    int temp2 = analogRead(2);
    int temp3 = analogRead(3);
    text[i] = (temp0/8)-1;
    text[i+1] = ',';
    text[i+2] = (temp1/8)-1;
    text[i+3] = ',';
    text[i+4] = (temp2/8)-1;
    text[i+5] = ',';
    text[i+6] = (temp3/8)-1;
    text[i+7] = '\n';

Now it’s possible to save and study data right from RTC circuit and motherboard.

Power Supply for old computer

AT standard compliant power lines are +12V, +5V, -12V and -5V. Positive voltages are easy to supply with normal mains adapter, but negative ones are harder to get. Below is schematic of my power supply. It is tested and works ok. Motherboard will start normally.

Photo of the same thing. Other adapter will transform ATX connector to AT P8 and P9 connectors.

-12V is mainly used in serial communication. -5V seems to be used in display adapter board in some sort of op-amp kind of thingy. 🙂 Display is very dim without it.

Self made Cell Phone

I built a cellular phone. It has a touchpad from old laptop and small LCD display. GSM module is SIM800L. Heart of a phone is Arduino Nano. Next I’am going to write a program to it so I can make and receive calls. Touchpad is very unique user interface. Case is made from plastic from old laptop.

Touchpad uses PS2 protocol. GSM modem uses softwareSerial library and LCD display is HD44780 compatible.




There is a place for SIM card in side of a phone and micro USB connector for normal phone charger. Back door is easily removable. It is fixed with magnet.

Optimization and improvements

Some enhangements to second prototype of New RTC Replacement Module. New circuit board is ordered from China and is coming soon.

Improved schematic diagram. Added memory capacitor and support circuit that allows use of smaller limiting voltage capacitors. PCF8563 is deprecated and replaced with PCM8583. Program code needs appropriate changes too.

Prototype is ready for testing

Ready made prototype of New RTC Replacement Module. Battery is replaced with 0.68F memory capacitor.

To transfer program in to AVR which has Arduino bootloader installed is possible with USB to UART board. Only one 100nF capacitor is needed.

Connection UART – AVR
  • GND – GND
  • +5V – +5V
  • TX – RX
  • RX – TX
  • DTR – 100nF cap – RESET

New RTC Replacement Module

Old computers often does not work because of worn out backup battery on the motherboard. That battery keeps RTC, Real Time Clock running. Without it BIOS can not start operating system or at least there is some serious errors in startup.

In many cases that battery is not changeable. It is molded inside of RTC module. Module type is Dallas DS12887 or similar. One can buy new module from eBay on example, but it is NOS, New Old Stock because that part is obsolete. Batteries often worns out even without use in about ten years.

Solution is to remove old DS12887 module from motherboard and put own circuit in place.

This circuit is compatible with Arduino and Arduino IDE can be used to program it directly. Arduino is programmed with code that mimics all functions that ds12887 have.


Using graphic Nokia 3310/5110 display with Arduino

This monochrome display uses Philips PCD8544 internal driver chip. It is fun to program and use.

Display works only at 3.3V and have 3V communication levels. So level sifter is needed. Below is schematics. Two pins can be saved by connecting CS to ground and reset to Arduino reset pin. It will reset the screen automatically.

Driver code for display. For graphic operations use LcdWrite function directly.

const byte PIN_DC = 5;
const byte PIN_SDIN = 4;
const byte PIN_SCLK = 3;

// send instruction command or data
const boolean LCD_C = LOW;
const boolean LCD_D = HIGH;

// width and height of display
const byte LCD_X = 84;
const byte LCD_Y = 48;

static const byte ASCII[][5] =
 {0x00, 0x00, 0x00, 0x00, 0x00} // 20  
,{0x00, 0x00, 0x5f, 0x00, 0x00} // 21 !
,{0x00, 0x07, 0x00, 0x07, 0x00} // 22 "
,{0x14, 0x7f, 0x14, 0x7f, 0x14} // 23 #
,{0x24, 0x2a, 0x7f, 0x2a, 0x12} // 24 $
,{0x23, 0x13, 0x08, 0x64, 0x62} // 25 %
,{0x36, 0x49, 0x55, 0x22, 0x50} // 26 &
,{0x00, 0x05, 0x03, 0x00, 0x00} // 27 '
,{0x00, 0x1c, 0x22, 0x41, 0x00} // 28 (
,{0x00, 0x41, 0x22, 0x1c, 0x00} // 29 )
,{0x14, 0x08, 0x3e, 0x08, 0x14} // 2a *
,{0x08, 0x08, 0x3e, 0x08, 0x08} // 2b +
,{0x00, 0x50, 0x30, 0x00, 0x00} // 2c ,
,{0x08, 0x08, 0x08, 0x08, 0x08} // 2d -
,{0x00, 0x60, 0x60, 0x00, 0x00} // 2e .
,{0x20, 0x10, 0x08, 0x04, 0x02} // 2f /
,{0x3e, 0x51, 0x49, 0x45, 0x3e} // 30 0
,{0x00, 0x42, 0x7f, 0x40, 0x00} // 31 1
,{0x42, 0x61, 0x51, 0x49, 0x46} // 32 2
,{0x21, 0x41, 0x45, 0x4b, 0x31} // 33 3
,{0x18, 0x14, 0x12, 0x7f, 0x10} // 34 4
,{0x27, 0x45, 0x45, 0x45, 0x39} // 35 5
,{0x3c, 0x4a, 0x49, 0x49, 0x30} // 36 6
,{0x01, 0x71, 0x09, 0x05, 0x03} // 37 7
,{0x36, 0x49, 0x49, 0x49, 0x36} // 38 8
,{0x06, 0x49, 0x49, 0x29, 0x1e} // 39 9
,{0x00, 0x36, 0x36, 0x00, 0x00} // 3a :
,{0x00, 0x56, 0x36, 0x00, 0x00} // 3b ;
,{0x08, 0x14, 0x22, 0x41, 0x00} // 3c <
,{0x14, 0x14, 0x14, 0x14, 0x14} // 3d =
,{0x00, 0x41, 0x22, 0x14, 0x08} // 3e >
,{0x02, 0x01, 0x51, 0x09, 0x06} // 3f ?
,{0x32, 0x49, 0x79, 0x41, 0x3e} // 40 @
,{0x7e, 0x11, 0x11, 0x11, 0x7e} // 41 A
,{0x7f, 0x49, 0x49, 0x49, 0x36} // 42 B
,{0x3e, 0x41, 0x41, 0x41, 0x22} // 43 C
,{0x7f, 0x41, 0x41, 0x22, 0x1c} // 44 D
,{0x7f, 0x49, 0x49, 0x49, 0x41} // 45 E
,{0x7f, 0x09, 0x09, 0x09, 0x01} // 46 F
,{0x3e, 0x41, 0x49, 0x49, 0x7a} // 47 G
,{0x7f, 0x08, 0x08, 0x08, 0x7f} // 48 H
,{0x00, 0x41, 0x7f, 0x41, 0x00} // 49 I
,{0x20, 0x40, 0x41, 0x3f, 0x01} // 4a J
,{0x7f, 0x08, 0x14, 0x22, 0x41} // 4b K
,{0x7f, 0x40, 0x40, 0x40, 0x40} // 4c L
,{0x7f, 0x02, 0x0c, 0x02, 0x7f} // 4d M
,{0x7f, 0x04, 0x08, 0x10, 0x7f} // 4e N
,{0x3e, 0x41, 0x41, 0x41, 0x3e} // 4f O
,{0x7f, 0x09, 0x09, 0x09, 0x06} // 50 P
,{0x3e, 0x41, 0x51, 0x21, 0x5e} // 51 Q
,{0x7f, 0x09, 0x19, 0x29, 0x46} // 52 R
,{0x46, 0x49, 0x49, 0x49, 0x31} // 53 S
,{0x01, 0x01, 0x7f, 0x01, 0x01} // 54 T
,{0x3f, 0x40, 0x40, 0x40, 0x3f} // 55 U
,{0x1f, 0x20, 0x40, 0x20, 0x1f} // 56 V
,{0x3f, 0x40, 0x38, 0x40, 0x3f} // 57 W
,{0x63, 0x14, 0x08, 0x14, 0x63} // 58 X
,{0x07, 0x08, 0x70, 0x08, 0x07} // 59 Y
,{0x61, 0x51, 0x49, 0x45, 0x43} // 5a Z
,{0x00, 0x7f, 0x41, 0x41, 0x00} // 5b [
,{0x02, 0x04, 0x08, 0x10, 0x20} // 5c ¥
,{0x00, 0x41, 0x41, 0x7f, 0x00} // 5d ]
,{0x04, 0x02, 0x01, 0x02, 0x04} // 5e ^
,{0x40, 0x40, 0x40, 0x40, 0x40} // 5f _
,{0x00, 0x01, 0x02, 0x04, 0x00} // 60 `
,{0x20, 0x54, 0x54, 0x54, 0x78} // 61 a
,{0x7f, 0x48, 0x44, 0x44, 0x38} // 62 b
,{0x38, 0x44, 0x44, 0x44, 0x20} // 63 c
,{0x38, 0x44, 0x44, 0x48, 0x7f} // 64 d
,{0x38, 0x54, 0x54, 0x54, 0x18} // 65 e
,{0x08, 0x7e, 0x09, 0x01, 0x02} // 66 f
,{0x0c, 0x52, 0x52, 0x52, 0x3e} // 67 g
,{0x7f, 0x08, 0x04, 0x04, 0x78} // 68 h
,{0x00, 0x44, 0x7d, 0x40, 0x00} // 69 i
,{0x20, 0x40, 0x44, 0x3d, 0x00} // 6a j 
,{0x7f, 0x10, 0x28, 0x44, 0x00} // 6b k
,{0x00, 0x41, 0x7f, 0x40, 0x00} // 6c l
,{0x7c, 0x04, 0x18, 0x04, 0x78} // 6d m
,{0x7c, 0x08, 0x04, 0x04, 0x78} // 6e n
,{0x38, 0x44, 0x44, 0x44, 0x38} // 6f o
,{0x7c, 0x14, 0x14, 0x14, 0x08} // 70 p
,{0x08, 0x14, 0x14, 0x18, 0x7c} // 71 q
,{0x7c, 0x08, 0x04, 0x04, 0x08} // 72 r
,{0x48, 0x54, 0x54, 0x54, 0x20} // 73 s
,{0x04, 0x3f, 0x44, 0x40, 0x20} // 74 t
,{0x3c, 0x40, 0x40, 0x20, 0x7c} // 75 u
,{0x1c, 0x20, 0x40, 0x20, 0x1c} // 76 v
,{0x3c, 0x40, 0x30, 0x40, 0x3c} // 77 w
,{0x44, 0x28, 0x10, 0x28, 0x44} // 78 x
,{0x0c, 0x50, 0x50, 0x50, 0x3c} // 79 y
,{0x44, 0x64, 0x54, 0x4c, 0x44} // 7a z
,{0x00, 0x08, 0x36, 0x41, 0x00} // 7b {
,{0x00, 0x00, 0x7f, 0x00, 0x00} // 7c |
,{0x00, 0x41, 0x36, 0x08, 0x00} // 7d }
,{0x10, 0x08, 0x08, 0x10, 0x08} // 7e ←
,{0x78, 0x46, 0x41, 0x46, 0x78} // 7f →

void LcdCharacter(char character) {
  for (int index = 0; index < 5; index++) {
    LcdWrite(LCD_D, ASCII[character - 0x20][index]);
  LcdWrite(LCD_D, 0x00);

void LcdClear(void) {
  // fill with blanks
  for (int index = 0; index < LCD_X * LCD_Y / 8; index++) {
    LcdWrite(LCD_D, 0x00);
  // reset cursor position
  LcdWrite(LCD_C, 0x80);
  LcdWrite(LCD_C, 0x40);

void LcdInitialise(void) {
  pinMode(PIN_DC, OUTPUT);
  pinMode(PIN_SDIN, OUTPUT);
  pinMode(PIN_SCLK, OUTPUT);
  LcdWrite(LCD_C, 0x21 );  // LCD Extended Commands.
  LcdWrite(LCD_C, 0xB1 );  // Set LCD Vop (Contrast). 
  LcdWrite(LCD_C, 0x04 );  // Set Temp coefficent. //0x04
  LcdWrite(LCD_C, 0x14 );  // LCD bias mode 1:48. //0x13
  LcdWrite(LCD_C, 0x20 );  // LCD Basic Commands
  LcdWrite(LCD_C, 0x0C );  // LCD in normal mode.

void LcdString(char *characters) {
  while (*characters) {

void LcdWrite(byte dc, byte data) {
  digitalWrite(PIN_DC, dc);
  shiftOut(PIN_SDIN, PIN_SCLK, MSBFIRST, data);

void setup(void) {
  LcdString("Juvar's blog");

void loop(void) {
  // nothing here


SPI controlled display with SD card reader

Using SD card to load image on to display. Must use 2.8…3.3V external power supply or resistive level sifter. Remove SD card before connecting to USB and transferring program to Arduino.

Connect external power supply to 5V output pin. It does not harm Arduino in any way. Remove power supply connection before connecting USB or it will harm computer.

Arduino connection
  • SCLK (Serial Clock) to pin D13
  • MISO (Master Input ← Slave Output) to pin D12
  • MOSI (Master Output → Slave Input) to pin D11
  • TFT_CS (TFT display Chip Select) to pin D10
  • D/C (Data/Control) to pin D9
  • Reset to pin D8
  • SD_CS (SD card Chip Select) to pin D4

Adafruits example code for reading image from SD card and display it on screen. It is licensed with MIT license. Image must be in root directory in BMP format. SD card must be formatted to FAT16 or FAT32 format.

  This is an example sketch for the Adafruit 2.2" SPI display.
  This library works with the Adafruit 2.2" TFT Breakout w/SD card
  ----> http://www.adafruit.com/products/1480
  Check out the links above for our tutorials and wiring diagrams
  These displays use SPI to communicate, 4 or 5 pins are required to
  interface (RST is optional)
  Adafruit invests time and resources providing this open source code,
  please support Adafruit and open-source hardware by purchasing
  products from Adafruit!

  Written by Limor Fried/Ladyada for Adafruit Industries.
  MIT license, all text above must be included in any redistribution

#include <Adafruit_GFX.h>    // Core graphics library
#include "Adafruit_ILI9340.h" // Hardware-specific library
#include <SPI.h>
#include <SD.h>

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

// TFT display and SD card will share the hardware SPI interface.
// Hardware SPI pins are specific to the Arduino board type and
// cannot be remapped to alternate pins.  For Arduino Uno,
// Duemilanove, etc., pin 11 = MOSI, pin 12 = MISO, pin 13 = SCK.
#define TFT_RST 8
#define TFT_DC 9
#define TFT_CS 10
#define SD_CS 4

Adafruit_ILI9340 tft = Adafruit_ILI9340(TFT_CS, TFT_DC, TFT_RST);

void setup(void) {

  Serial.print("Initializing SD card...");
  if (!SD.begin(SD_CS)) {


  bmpDraw("myy.bmp", 0, 0);

void loop() {

// This function opens a Windows Bitmap (BMP) file and
// displays it at the given coordinates.  It's sped up
// by reading many pixels worth of data at a time
// (rather than pixel by pixel).  Increasing the buffer
// size takes more of the Arduino's precious RAM but
// makes loading a little faster.  20 pixels seems a
// good balance.

#define BUFFPIXEL 20

void bmpDraw(char *filename, uint16_t x, uint16_t y) {

  File     bmpFile;
  int      bmpWidth, bmpHeight;   // W+H in pixels
  uint8_t  bmpDepth;              // Bit depth (currently must be 24)
  uint32_t bmpImageoffset;        // Start of image data in file
  uint32_t rowSize;               // Not always = bmpWidth; may have padding
  uint8_t  sdbuffer[3*BUFFPIXEL]; // pixel buffer (R+G+B per pixel)
  uint8_t  buffidx = sizeof(sdbuffer); // Current position in sdbuffer
  boolean  goodBmp = false;       // Set to true on valid header parse
  boolean  flip    = true;        // BMP is stored bottom-to-top
  int      w, h, row, col;
  uint8_t  r, g, b;
  uint32_t pos = 0, startTime = millis();

  if((x >= tft.width()) || (y >= tft.height())) return;

  Serial.print("Loading image '");

  // Open requested file on SD card
  if ((bmpFile = SD.open(filename)) == NULL) {
    Serial.print("File not found");

  // Parse BMP header
  if(read16(bmpFile) == 0x4D42) { // BMP signature
    Serial.print("File size: "); Serial.println(read32(bmpFile));
    (void)read32(bmpFile); // Read & ignore creator bytes
    bmpImageoffset = read32(bmpFile); // Start of image data
    Serial.print("Image Offset: "); Serial.println(bmpImageoffset, DEC);
    // Read DIB header
    Serial.print("Header size: "); Serial.println(read32(bmpFile));
    bmpWidth  = read32(bmpFile);
    bmpHeight = read32(bmpFile);
    if(read16(bmpFile) == 1) { // # planes -- must be '1'
      bmpDepth = read16(bmpFile); // bits per pixel
      Serial.print("Bit Depth: "); Serial.println(bmpDepth);
      if((bmpDepth == 24) && (read32(bmpFile) == 0)) { // 0 = uncompressed

        goodBmp = true; // Supported BMP format -- proceed!
        Serial.print("Image size: ");

        // BMP rows are padded (if needed) to 4-byte boundary
        rowSize = (bmpWidth * 3 + 3) & ~3;

        // If bmpHeight is negative, image is in top-down order.
        // This is not canon but has been observed in the wild.
        if(bmpHeight < 0) {
          bmpHeight = -bmpHeight;
          flip      = false;

        // Crop area to be loaded
        w = bmpWidth;
        h = bmpHeight;
        if((x+w-1) >= tft.width())  w = tft.width()  - x;
        if((y+h-1) >= tft.height()) h = tft.height() - y;

        // Set TFT address window to clipped image bounds
        tft.setAddrWindow(x, y, x+w-1, y+h-1);

        for (row=0; row<h; row++) { // For each scanline...

          // Seek to start of scan line.  It might seem labor-
          // intensive to be doing this on every line, but this
          // method covers a lot of gritty details like cropping
          // and scanline padding.  Also, the seek only takes
          // place if the file position actually needs to change
          // (avoids a lot of cluster math in SD library).
          if(flip) // Bitmap is stored bottom-to-top order (normal BMP)
            pos = bmpImageoffset + (bmpHeight - 1 - row) * rowSize;
          else     // Bitmap is stored top-to-bottom
            pos = bmpImageoffset + row * rowSize;
          if(bmpFile.position() != pos) { // Need seek?
            buffidx = sizeof(sdbuffer); // Force buffer reload

          for (col=0; col<w; col++) { // For each pixel...
            // Time to read more pixel data?
            if (buffidx >= sizeof(sdbuffer)) { // Indeed
              bmpFile.read(sdbuffer, sizeof(sdbuffer));
              buffidx = 0; // Set index to beginning

            // Convert pixel from BMP to TFT format, push to display
            b = sdbuffer[buffidx++];
            g = sdbuffer[buffidx++];
            r = sdbuffer[buffidx++];
          } // end pixel
        } // end scanline
        Serial.print("Loaded in ");
        Serial.print(millis() - startTime);
        Serial.println(" ms");
      } // end goodBmp

  if(!goodBmp) Serial.println("BMP format not recognized.");

// These read 16- and 32-bit types from the SD card file.
// BMP data is stored little-endian, Arduino is little-endian too.
// May need to reverse subscript order if porting elsewhere.

uint16_t read16(File & f) {
  uint16_t result;
  ((uint8_t *)&result)[0] = f.read(); // LSB
  ((uint8_t *)&result)[1] = f.read(); // MSB
  return result;

uint32_t read32(File & f) {
  uint32_t result;
  ((uint8_t *)&result)[0] = f.read(); // LSB
  ((uint8_t *)&result)[1] = f.read();
  ((uint8_t *)&result)[2] = f.read();
  ((uint8_t *)&result)[3] = f.read(); // MSB
  return result;


SPI controlled TFT display

Normal Arduino SPI TFT display library does not work with cheap TFT displays with integrated ILI9340C controller chip. Display model is TM022HDH26. Hopefully there is two libraries made by Adafruit that works together and brings display to live. Those are easy to install from Arduino IDE Library Manager. Needed libraries are Adafruit GFX Library and Adafruit_ILI9340. Result is below.

Arduino connection
  • SCLK (Serial Clock) to pin D13
  • MOSI (Master Output → Slave Input) to pin D11
  • CS (Chip Select) to pin D10
  • D/C (Data/Control) to pin D9
  • Reset to pin D8

Simple example code for testing.

#include "SPI.h"
#include "Adafruit_GFX.h"
#include "Adafruit_ILI9340.h"

// pin definition
const byte CS = 10;
const byte DC = 9;
const byte RS = 8;

Adafruit_ILI9340 scr = Adafruit_ILI9340(CS, DC, RS);

void setup() {
  scr.println("Electronics Corner");
  scr.println("All kinds of electronics");
  scr.println("Testing display with");
  scr.println("ILI9340C controller.");

void loop() {
  // nothing here