Alarm System Keypad — Dylan Zickus

Overview

This project was an educational exercise in electronics and microcontroller programming, resulting in an alarm system featuring a keypad, indicator LEDs, a buzzer, and a magnetic door sensor[cite: 1, 2]. Though the system worked effectively—including virtual arming/disarming and alerts via Home Assistant—it was never permanently installed. The breadboard circuit eventually came apart, and planned features, such as a deadbolt motor, were ultimately not realized.

Hardware

Microcontroller: ESP8266 / ESP32
Keypad: Transitioned from a 7-pin digital matrix[cite: 1] to a 1-pin analog resistor ladder[cite: 2]
Sensors: Magnetic door reed switch using internal pull-up[cite: 2, 3]
Indicators: Green, Red, and Yellow LEDs[cite: 1, 2]
Audio: Passive Buzzer[cite: 1, 2]

The hardware evolved significantly to accommodate microcontroller limitations. Initially relying on 7 distinct GPIO pins for a standard matrix keypad[cite: 1], the system was redesigned to utilize resistor math, allowing the entire keypad to be read through a single analog pin[cite: 2].

Iteration History

Stage 1 — Digital Matrix Keypad (`simple_alarm.ino`)

The initial prototype used a standard digital scanning method to read the keypad[cite: 1]. The firmware utilized the standard Keypad.h library to map a 4-row by 3-column matrix layout[cite: 1].

const byte ROWS = 4;
const byte COLS = 3;
byte rowPins[ROWS] = {5, 4, 0, 2};
byte colPins[COLS] = {14, 12, 13};
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

This matrix required a total of 7 GPIO pins mapped to the microcontroller[cite: 1]. Because the standard method sequentially pulses input lanes and listens on output lanes, it consumed too many pins and severely limited the small microcontroller.

Stage 2 — Analog Resistor Keypad (`alarm_panel.ino`)

To conserve GPIO pins, the keypad was redesigned using resistor math to output a specific analog voltage for each button press, condensed down to a single analog input on pin 13[cite: 2].

Analog Threshold Mapping. The microcontroller read the analog voltage and mapped it against an array of 16 descending threshold values[cite: 2]. These values started from 4097 down to 220[cite: 2].

int value = analogRead(keypad_pin);
if (value != 0) {
  for (int i = 15; i >= 0; i--) {
    if (value < values[i]) {
      readSymbol(symbols[i]);
      value = 5000; // Break out
    }
  }
}

While this method worked perfectly for individual presses mapping exact symbols, the physical nature of the resistor logic caused unexpected behavior when multiple keys were pressed simultaneously.

Stage 3 — Sensor Diagnostics (`basic_reed_sensor.ino`)

During development, a simple diagnostic script was used to verify sensor behavior. * The script monitored a sensor connected to pin 13 configured with an internal pull-up resistor (INPUT_PULLUP)[cite: 3]. * It tracked the digital state of the sensor and printed the result to the serial monitor at continuous 100-millisecond intervals[cite: 3].

Architecture Diagram

┌─────────────────────────────────┐
│         Resistor Keypad         │
│  16 buttons mapped to voltages  │
└────────────┬────────────────────┘
             │ Analog Input (Pin 13)
             ▼
┌─────────────────────────────────┐
│         Microcontroller         │
│  - Threshold parsing[cite: 2]  │
│  - State management (Armed)     │
└────────────┬────────────────────┘
             │ Digital Outputs
             ▼
┌─────────────────────────────────┐
│         Status & Audio          │
│  Green/Red/Yellow LEDs[cite: 2]│
│  Passive Buzzer[cite: 2]       │
└─────────────────────────────────┘

What Works

Analog threshold mapping successfully detects all 16 unique individual button presses[cite: 2].
Virtual arming, disarming, and alert notifications through Home Assistant integrations.

Known Limitations & Future Work

Stacked Voltages. Combinations of multiple buttons pressed simultaneously trigger unexpected behavior due to stacked voltages in the resistor ladder. Physical finishing. The circuit was purely a breadboard prototype. It was never permanently installed or soldered, and eventually fell apart. Planned features, like a motorized deadbolt lock, were never built.

Tech Stack

Layer	Technology
Microcontroller	ESP8266 / ESP32
Firmware	Arduino (C++) — Keypad.h[cite: 1]
Inputs	Matrix Keypad, Magnetic Reed Switch[cite: 1, 2]
Outputs	Green, Red, Yellow LEDs, Passive Buzzer[cite: 1, 2]