Arduino 4 Digit LED 7-Segment Countdown Timer based on Arduino MEGA will be shown in this post. For LCD version of this design follow this link. Similar project that uses PIC16F876 MCU can be found at this link. Raspberry Pi version is also available here. Countdown timer will accept 4-digit initial value from 4×3 membrane keypad and then start counting till it reaches zero. 4 Digit display module is driven by TM1637 chip. This is a very popular and commonly used component. There are many variants of these modules but they all require 4 signals from Arduino: VDD,GND,CLK and Data input. The schematic diagram is shown next.
In order to interface with 7-Segment driver TM1637Display.h library need to be added to Arduino IDE. When the counter at 0000 the buzzer connected to A0 output of Arduino MEGA board will be turned ON. Entering a new value can’t be done during the counter operation. You can wait for 0000 count or reset the board and then enter an updated value from the keypad. Arduino sketch available here.
For high current loads connect A0 output to a relay or solid state switch. You can also output a constant voltage instead of blinking by modifying IfZero() function in the attached code.