PAGE 150 OF 150 · PROJECTS
Build a Countdown Timer Display
Counting down digits show remaining time.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
What it does
A countdown timer shows minutes and seconds on a four-digit display, counts down once a second and signals when it reaches zero.
Build
- Use a ready-made four-digit module such as one based on the TM1637 or MAX7219 to save pins.
- Add buttons for set minutes, set seconds and start or pause.
- Use the millis counter to subtract exactly one second each time, not delays.
- At zero, flash the display and sound a buzzer.
Accuracy
Ordinary development boards use a resonator that may drift by seconds per day. For long countdowns add a real-time clock chip.
REMEMBER
Time from a counter, not from delay calls.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
Explore LED clocks, stopwatches and electronics at cosycom.com.