In order to carry out this project, I had to call on a PCB manufacturing company in China which manufactured the necessary circuits from the drawings that I produced using KiCad software.

Project Overview

The "Sentinel-Alpha Advanced Timer" is a transition from hobbyist prototyping to professional embedded systems engineering. While basic timers are common, this iteration incorporates Industrial Design principles, including custom multi-layer PCB fabrication, ruggedized IP67 enclosures, and specialized Fisher/M12 connectors. Built around an Arduino Nano, the system serves as a precise temporal controller capable of driving external relays and high-power high-current industrial loads.

Technical Deep-Dive: PCB Architecture & KiCad Design

Modular Control Bus: The project utilizes custom PCBs designed in KiCad EDA. The control board isolates the logic (Nano) from the power switching (Relay), utilizing wide ground planes to minimize Electromagnetic Interference (EMI) from the high-voltage switching events.
Professional Fabrication: The circuits feature silk-screened labels and gold-flash plating (ENIG) for improved solderability and corrosion resistance in humid environments.

The display and the control board on KiCad:

Here are the circuits made by the manufacturers, I am ordering 10 pieces of each.

Technical Deep-Dive: Core System Design

Here you can see the progress of production. The final programmable timer uses an Arduino NANO where I assigned pins "10, 11, 12" for the display, "6, 7, 8, 9" for the horizontals of the keypad, and "2, 3, 4, 5" for the columns.

MAX7219 Multiplexing Engine: The 7-segment display is driven by the MAX7219 serially-interfaced controller. Instead of using 28 pins for four digits, it handles the 8x8 LED matrix multiplexing internally via a 3-wire SPI link (Pins 10, 11, 12), significantly reducing the IO overhead on the Nano. The firmware dynamically adjusts the PWM brightness of the LED digits via the MAX7219's internal Scan-Limit and Intensity registers.
Software State Machine Logic: The 4x4 keypad utilizes a Polling-Based Scanning Routine. Key "A" initializes the programming buffer, "B" handles the Asynchronous Pause via a volatile boolean flag, "C" executes a buffer-clear, and "D" triggers the countdown logic.
Relay Actuation Loop: The integrated relay is tied to pin A1, utilized here as a digital output. Upon the counter reaching zero, the Nano sends a HIGH signal to an NPN transistor/optocoupler circuit, energizing the relay coil to trigger external sirens or machinery.

The buzzer is connected to the analog pin "A0". A relay is integrated into the control board and assigned to the analog pin “A1” of the Arduino, it turns on by default when the countdown reaches 0.

Engineering & Implementation: Ruggedized Assembly

The rest of the manufacturing mainly consists of dressing the waterproof box, notably by adding high quality waterproof connectors and a wireless on and off module.

Ruggedized Interface (Connectors): Power connector for battery charging, Fisher 0B type 8-pin self-locking connector for the numeric keypad (ensuring mechanical vibration won't result in signal loss), and an 8-pin M12 connector for I/O with +3.3/5V and GND, providing standardized access for secondary sensors.
Advanced Power Management: The system is powered by high-capacity 18650 Li-ion cells. The internal power rail is regulated via a buck-boost converter to ensure stable 5V logic regardless of battery discharge state.
Wireless Override: The wireless on and off module is actually a kit ordered on internet (typically 433MHz or 2.4GHz), allowing for remote emergency stops or manual starts, bypassing the keypad in urgent scenarios.
Waterproof Integration: The entire assembly is housed in a high-impact enclosure with rubberized gaskets. Every hole for displays and switches is sealed with industrial-grade adhesives to maintain the IP-rating for outdoor use.

Software & Functionality

For the code, I improved by adding a few more functions, now in addition to programming the time with the 'A' key, and the start with the 'D' key, it is also possible to set pause the countdown by pressing the 'B' key and start again with the 'D' key, in the event of an error in programming mode, press the 'C' key, then press the 'A' key again to reprogram the desired time.

I am also thinking of adding an I/O output assigned of analog output of the Arduino for connecting up to 5 external modules such as relays, sensors, etc..., with GND, 3.3V, and 5V output.

Conclusion

By combining custom hardware with a robust software state machine, the sentinel-alpha timer provides a reliable timing solution that bridges the gap between a classroom project and an industrial tool.

Time under control: Merging professional PCB design with rugged industrial execution.