Devlog #1: From Macropad Inspiration to Standalone Hardware

💡 The Spark of Inspiration

Initially, I wanted to build a simple 4-button macropad with a volume knob using an Arduino Uno. But as I started thinking about what would actually be useful day-to-day, I pivoted the idea into a Physical Money Tracker—a desktop device that lets me quickly log financial transactions with the twist of a dial and the press of a single button.

I decided to challenge myself: Ax the PC and PyCharm entirely. I wanted a 100% standalone hardware device that works on raw micro-controller logic and remembers my balance even if I unplug it.

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🛠️ Designing the Architecture

Instead of hiding data on a computer screen, I dug out a 5461AS 4-digit 7-segment display to show my data directly on my desk.

The control flow is clean and tactile:

• The Dial (B10K Potentiometer): Acts as an amount selector. Turning it scrolls through transaction amounts (-20, -10, 0, +10, +20).
• The Confirmation (Push Button): Acts as the “Enter” key to commit the transaction.
• The Feedback (Active Buzzer): Gives a tiny “click” sound when shifting between numbers, and a satisfying double-beep when a transaction successfully saves.

Because I wanted it to be standalone, I utilized the Arduino’s EEPROM memory so my balance data survives power loss.

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🎛️ Mapping the Complex Matrix

The hardest part of the prototype was figuring out the routing for the 5461AS display. Without a dedicated driver chip, it requires 12 independent pin connections. I mapped out a custom configuration to keep the standard digital pins (D2 and D3) free for my tactile inputs:

• Digits (Left to Right): Pins 12, 13, A1, A2 -> Connected to D12, D13, A1, A2
• Segments (A through G + DP): Connected to D4, D5, D6, D7, D8, D9, D10, D11
• Inputs: Potentiometer on A0, Button on D2, Buzzer on D3

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💻 Prototype Core Firmware Logic

I integrated the SevSeg library to handle the rapid background multiplexing needed to keep the display lit without flickering. Here is the core operational loop of the system:

void loop() {
  int potValue = analogRead(POT_PIN);
  int potZone = potValue / 205; 
  
  switch(potZone) {
    case 0: selectedAction = -20; break;
    case 1: selectedAction = -10; break;
    case 2: selectedAction = 0;   break;
    case 3: selectedAction = 10;  break;
    case 4: selectedAction = 20;  break;
  }

  // Handle Button Press and Save to EEPROM
  int buttonState = digitalRead(BUTTON_PIN);
  if (buttonState == LOW && lastButtonState == HIGH) {
    currentBalance += selectedAction;
    saveBalance(currentBalance); // EEPROM storage
    
    sevSeg.blank();
    tone(BUZZER_PIN, 2700); delay(80); noTone(BUZZER_PIN);     
    delay(40);
    tone(BUZZER_PIN, 2700); delay(80); noTone(BUZZER_PIN);
  }
  lastButtonState = buttonState;

  if (buttonState == HIGH) {
     sevSeg.setNumber(selectedAction); 
  } else {
     sevSeg.setNumber(currentBalance);
  }
  sevSeg.refreshDisplay(); 
}