This is a 4x4 keypad that blinks an led several times based on which key has been pressed. Built using an atmega328p, a 4x4 keypad, a resistor and led. The code runs on C.

Basic components required are:

1. Microcontroller (Atmega 328p-pu)
2. Crystal for timing operations (16Mhz crystal)
3. Resistor (10 kilohms)
4. Power source
5. Wires (male to female and male to male wires)
6. A programmer (usbtinyisp or any other)
7. Board (copper board or bread board)
8. Wires
9. Led

Set up the circuit as shown in the figure below

A video of the code running

In this case I was using the terminal from linux

Install avr gcc by running the following command

sudo apt-get install gcc-avr binutils-avr avr-libc

Install avrdude by running

sudo apt-get install avrdude

To upload the code to the chip, one can run these commands:

The following compiles the code to a .obj file

avr-gcc -g -Os -Wall -mcall-prologues -mmcu=atmega328p -fno-exceptions -o main.obj main.c

The following code compiles the code to a .hex file

avr-objcopy -R .eeprom -O ihex main.obj main.hex

The following code uploads the .hex file to the chip (in this case I was using a usbtinyisp)

avrdude -b 19200 -c usbtiny -p m328p -U flash:w:main.hex para gravar no atmega

This are the references I used

1. Patrick Hood Daniel, using a 4x4 keypad https://www.youtube.com/watch?v=6FjrKXmquxU&t=898s

2. Avr Microcontroller and Embedded Systems The: Using Assembly and C Book by Muhammad Ali Mazidi, Sarmad Naimi, and Sepehr Naimi