Project Description : The custom detection timer is a motion-activated countdown system designed to provide intuitive and accurate timing control using embedded electronics. At its core, the system utilizes an Arduino Uno microcontroller, which integrates inputs from a PIR motion sensor, a potentiometer, and various user-operated buttons. The PIR sensor acts as the system's trigger, detecting the presence and removal of an object (e.g., a phone) placed within its sensing range. When motion is no longer detected, a countdown is initiated, and upon timer expiration, an audio alarm plays at a frequency determined by the potentiometer. The countdown duration is selectable via a mode toggle button, allowing users to switch between 5-minute and 10-minute timer presets. Visual feedback is provided in real time on an LCD display, which shows the remaining time, current frequency, and status messages. The LCD backlight brightness can be adjusted through three dedicated buttons offering 100%, 75%, and 50% brightness levels using PWM control. The system's construction prioritizes portability, modularity, and safety. It is powered by a 14V battery regulated down to 7V using an LM2596 buck converter, which supplies stable voltage to the Arduino and all peripherals. Custom code uploaded via the Arduino IDE manages sensor polling, timer logic, frequency mapping, and user interface responsiveness. One of the key engineering challenges during development was ensuring smooth communication and synchronization between hardware components—especially coordinating sensor state changes with timer actions and display updates. With careful use of millis() for timing and debouncing techniques for button inputs, the system achieves real-time performance and minimal flicker on the display. While deadlines were tight, the team was able to meet all major engineering requirements, including IP40-compliant assembly, ±1 second response accuracy, and an intuitive user interface that most users could operate without instruction