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Sangster's AVR Library

This library provides helpful code for developing toy projects with the ATmega328P AVR microcontroller. You likely don't want to use this for anything critical, as it was developed mainly as a learning tool to teach myself embedded development.

It is a "Header-Only" library. The main reason for this is that this library relies on DEFINEs that aren't available until your application is compiled. For example, many functions rely on F_CPU to inform them of your device's clock-speed. A secondary benefit is that avr-gcc seems to be able to compile smaller binaries this way.

Getting Started

As this is a header-only library, you don't need to link any additional object files. The headers will be installed in the standard AVR include directory, so you can build your project the same way as before. ex:

avr-gcc -mmcu=atmega328p -DF_CPU=12345678L ...


You can install this library on the local system with:

git clone ""
cd libsangster_avr
./ && sudo make install

Alternatively, on Arch Linux, you can use the provided PKGBUILD file to install this library with the package manager:

makepkg -s
pacman -U libsangster_avr-*.pkg.tar.xz


HD-44780 LCD

For Device: Generic Hitachi 2x16 character LCD screen

The super-common 2x16 character LCD screen. There seem to be a million different versions of this LCD screen, so the model code may be different for you.

  • #include <sangster/lcd.h> Functions for writing characters to the LCD.
  • #include <sangster/lcd_charmap.h> Defines constants for the extra characters supported by the controller.


For Device: PCD8544 LCD Controller.

The Nokia 5110 a small b/w, 84x48, LCD screen driven by a PCD8544 controller. This module utilities for communicating with the device, as well as functions for basic drawing, text, bitmaps, and transactions.

  • #include <sangster/pcd8544.h> Include all the PCD8544-related code.
  • #include <sangster/pcd8544/core.h> Functions for communicating with the device.
  • #include <sangster/pcd8544/draw.h> Functions for drawing simple shapes. You can fill indivitual pixels, lines, circles, and rectangles.
  • #include <sangster/pcd8544/text.h> Functions for drawing text. img2pcd8544 can be used to generate a font header file from an image file.
  • #include <sangster/pcd8544/bmp.h> Functions for drawing bitmaps. img2pcd8544 can be used to generate a bitmap header file from an image file.
  • #include <sangster/pcd8544/transaction.h> Functions for drawing transactions. To avoid inefficently communicating with the device after every change, you can compose the entire screen in memory, then draw it on the device in a single pass.

Example code

This example program draws some shapes int the center of the screen, then shows a counter at the top of the screen that is incrmented four times per second.

#include <stdio.h>
#include <avr/interrupt.h>
#include <avr/io.h>
#include <avr/pgmspace.h>
#include <util/delay.h>
#include <sangster/pcd8544.h>
#include <sangster/pinout.h>

#define CX  (PCD_COLS / 2) // Center pixel, horizontally
#define CY  (PCD_ROWS / 2) // Center pixel, vertically

/// The LCD screen's pins and state
Pcd screen = {
    .pin_led  = PIN_DEF_ARDUINO_8,
    .pin_sce_ = PIN_DEF_ARDUINO_7,
    .pin_res_ = PIN_DEF_ARDUINO_6,
    .pin_dc   = PIN_DEF_ARDUINO_5,
    .pin_sdin = PIN_DEF_ATMEGA328P_MOSI,
    .pin_sclk = PIN_DEF_ARDUINO_10,
PcdDraw draw; ///< Interface for basical drawing primitives

// A 7x8 bitmap font for drawing the counter digits
const PROGMEM PcdBank DIGIT_BITMAP[] = {
   0x3e, 0x61, 0x51, 0x49, 0x45, 0x3e, 0x00, // '0'
   0x44, 0x42, 0x7f, 0x40, 0x40, 0x00, 0x00, // '1'
   0x62, 0x51, 0x51, 0x49, 0x49, 0x66, 0x00, // '2'
   0x22, 0x41, 0x49, 0x49, 0x49, 0x36, 0x00, // '3'
   0x18, 0x14, 0x52, 0x7f, 0x50, 0x10, 0x00, // '4'
   0x27, 0x45, 0x45, 0x45, 0x45, 0x39, 0x00, // '5'
   0x3c, 0x4a, 0x49, 0x49, 0x49, 0x30, 0x00, // '6'
   0x03, 0x01, 0x71, 0x09, 0x05, 0x03, 0x00, // '7'
   0x36, 0x49, 0x49, 0x49, 0x49, 0x36, 0x00, // '8'
   0x06, 0x49, 0x49, 0x49, 0x29, 0x1e, 0x00, // '9'
const PcdFont DIGITS =
    {.chars = DIGIT_BITMAP, .width = 7, .first = '0', .count = 10};

int main(void)
    pcd_setup(&screen);   // Turn on the screen
    pcd_clr_all(&screen); // The DDRAM state is unknown at startup. Blank it
    pcd_op_voltage(&screen, PCD_MAX_OP_VOLTAGE / 2); // Screen contrast to half

    pcd_draw_init(&draw, &screen); // Setup the drawing buffer

    sei(); // Enaable interrupts for _delay_ms(). This is unrelated to PCD8544

    // Draw a pointless circle and hollow square in the center of the screen
    pcd_circ(&draw, CX, CY, PCD_ROWS/3, PCD_BLACK);
    pcd_rect(&draw, CX + 0, CY + 0, CX + 20, CY + 20, PCD_BLACK);
    pcd_rect(&draw, CX + 2, CY + 2, CX + 18, CY + 18, PCD_WHITE);

    // Where to draw the text for it's horizontally centered
    const PcdIdx center = (PCD_COLS - pcd_text_width(DIGITS, 3)) / 2;
    uint8_t counter = 0;

    // Show a quarter-second counter at the top-center of the screen
    for (;;) {
        char str[4];
        sprintf(str, "%03d", counter++);
        pcd_print(&draw, &DIGITS, center, 0, str, PCD_BLACK);

Example app screenshot


MCU Pins

Encapsulates the code for managing individual pins

Ring Buffer

A simple Ring Buffer implementation

Realtime Clock (DS1307)

Read and write the current date/time from a RTC

FAT32 filesystem on an SD Card

This module is a C transcription of William Greiman's SD C++ library. It does almost everything you need with SD cards: read, write, list, create directories. However, it only has partial support for long filenames, so try to stick with 8.3 filenames for now.

Example code

This example creates (or appends to, if the file already exists) a file called EXAMPLE.TXT. Then writes a new line with the value of a counter every second.

#include <avr/interrupt.h>
#include <util/delay.h>
#include <sangster/pinout.h>
#include <sangster/sd.h>

SdClass SD = {
    .card = {
        .chip_select_pin = PIN_DEF_ATMEGA328P_SS,
        .mosi_pin        = PIN_DEF_ATMEGA328P_MOSI,
        .miso_pin        = PIN_DEF_ATMEGA328P_MISO,
        .clock_pin       = PIN_DEF_ATMEGA328P_SCK,

int main(void)
    if (!sd_begin(&SD, NULL)) {
        while (1); // SD Card error. See SD.card.error_code

    SdFile fp = sd_open(&SD, "EXAMPLE.TXT", O_WRITE | O_APPEND | O_CREAT);

    sei(); // Interrupts needed only for _delay_ms()

    uint8_t counter = 0;
    char str[4];

    for (;;) {
        itoa(scounter++, str, 10); // int 2 string
        sd_file_print(&file, str); // Write string to SD (buffered)
        sd_file_crlf(&fp);         // Write newline to SD (buffered)
        sd_file_sync(&fp);         // Syncronise SD buffer with physical card

Sonar (OSEPP HC-SR04)

For Device: HC-SR04 Sonar.

This module controls an ultrasonic transmitter/receiver. It can tell you how far away the sonar is from... something (in centimeters or inches).


This example app prints how far away the object in front of the sensor is. If that object gets close or father away, the new distance will be printed on a new line.

#include <util/delay.h>
#include <sangster/pinout.h>
#include <sangster/sonar.h>
#include <sangster/usart.h>

SonarState sonar = {
    .trigger   = PIN_DEF_ARDUINO_12,
    .capture   = {&TCCR1B, ICES1},
    .interrupt = {&TIFR1, ICF1},
    .overflow  = {&TIFR1, TOV1},
    .max_distance_cm = 200

int main(void)

    usart_init(9600, FORMAT_8N1);
    UCSR0B |= _BV(TXEN0);

    char str[10];
    uint16_t prev_reading = 0;
    for(;;) {
        const uint16_t reading = sonar_ping(&sonar);
        if (reading == prev_reading) {
        prev_reading = reading;

        utoa(reading / US_ROUNDTRIP_CM, str, 10);



  • #include <sangster/timer0.h> A simple timer backed by TIMER0. You can get the number of milliseconds or microseconds which have ellapsed since calling timer0_reset() with timer0_ms() or timer0_us(), respectively.


This example app performs some arbitrary long-running task, then reports (via USART) how long it took, in milliseconds.

#include <avr/interrupt.h>
#include <avr/io.h>
#include <sangster/timer0.h>
#include <sangster/usart.h>

    // This is required so the timer can keep time

int main(void)
    usart_init(9600, FORMAT_8N1);
    UCSR0B |= _BV(TXEN0);


    for(;;) {


        uint16_t ms = timer0_ms();
        usart_print("That took ");
        usart_println(" milliseconds.");


This module is a C transcription of Nicholas Zambetti's TWI C++ library.

#include <sangster/twi.h>



Utilities for reading and writing to the connected serial device (ex: your PC).

  • #include <sangster/usart.h> Functions for reading and writing
  • #include <sangster/usart_p.h> Functions for writing to the serial device from PGMSPACE.

Example code

This example app simple reads characters sent and echos them back. To avoid wasted memory, constant strings are served from PGMSPACE.

#include <sangster/usart.h>
#include <sangster/usart_p.h>

int main(void)
    usart_init(9600, FORMAT_8N1);
    UCSR0B |= _BV(RXEN0) | _BV(TXEN0);

    usart_print_P(PSTR("echo> "));
    for(;;) {
        const uint8_t in = usart_recv(); // blocks until data is available

        if (in == '\r') { // newlin received
          usart_print_P(PSTR("\necho> "));


Misc. utility functions

  • #include <sangster/util.h> Utility functions that have no other home


This project is licensed under the GPL License - see the LICENSE file for details

Special Thanks

  • William Greiman, for the SD C++ code
  • Nicholas Zambetti, for the TWI C++ code


A convenience library for developing toy projects with AVR microcontrollers








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