⏱️ Arduino IR Countdown Timer

A countdown timer of up to 99 minutes, controlled with an infrared remote and shown on a 4-digit 7-segment display as MM.SS.

_{Real photo of the build, edited with AI to remove the jumper wires so the components are easier to see.}

How it works

• At start-up, or after a reset, the display shows two horizontal bars on each digit.
• Start/pause sets the timer to 60:00, then starts and pauses the countdown.
• + / − change the time by 10 minutes, or by 1 minute below 10 minutes and near the 99-minute limit.
• Reset stops the timer and goes back to the bars.
• When the countdown reaches 00:00, the whole display blinks until you set a new time.

The four digits are multiplexed: the sketch lights one digit at a time for 2 ms and cycles through them continuously. The countdown uses millis() instead of delay(), so the display keeps refreshing and the remote stays responsive while it counts. Repeated IR codes within 300 ms are ignored, so holding a button down doesn't jump several steps.

Hardware

• Arduino Uno (or Nano)
• 4-digit 7-segment display, common cathode
• IR receiver (e.g. VS1838B) and a small NEC remote, like the 21-key ones in Arduino kits
• Breadboard and jumper wires, plus current-limiting resistors for the segments

Wiring

Arduino pin	Connected to
2 – 8	Segments A – G
A5	Decimal point
9 – 12	Digits 1 – 4 (common pins)
13	IR receiver OUT (VCC to 5V, GND to GND)

Remote commands

IR command	Action
0x43	Set 60:00 / start / pause
0x44	Reset
0x15	Add time
0x07	Remove time

Which button sends which code depends on the remote. Open the Serial Monitor at 115200 baud: every button you press is printed as Command received: 0x... Then change the CMD_* constants at the top of the sketch to the buttons you want.

Running it

Install the IRremote library (Library Manager → IRremote by Armin Joachimsmeyer, version 4.x), open Arduino_Timer.ino, choose Arduino Uno and click Upload.

Or with arduino-cli:

arduino-cli core install arduino:avr
arduino-cli lib install IRremote
arduino-cli compile -b arduino:avr:uno --upload -p <port> .