Polvoron Vendo Machine Documentation

Project Overview

This Arduino-based Vending Machine controls the dispensing of three different Polvoron flavors (Choco, Barnuts, and Milk) using continuous rotation servos and an HX711 load cell (scale) to verify successful item drops. It operates entirely on a 5-PHP coin acceptor system and utilizes an Adafruit SSD1306 OLED screen for the user interface.

Hardware Configuration

Component	Pin	Type	Purpose
OLED Display	I2C (A4/A5)	SSD1306	Displays UI, balance, and warnings.
HX711 Scale	DOUT: 3, CLK: 2	Load Cell	Verifies item drops using weight (dropThreshold = 6.0).
Coin Acceptor	Pin 4	Digital In	Detects 5-PHP coin pulses.
Button: Choco	Pin 8	Digital In (Pull-up)	Selects Choco flavor.
Button: Barnuts	Pin 9	Digital In (Pull-up)	Selects Barnuts flavor.
Button: Milk	Pin 10	Digital In (Pull-up)	Selects Milk flavor.
Servo: Choco	Pin 5	PWM Out	Rotates Choco dispensing coil.
Servo: Barnuts	Pin 6	PWM Out	Rotates Barnuts dispensing coil.
Servo: Milk	Pin 7	PWM Out	Rotates Milk dispensing coil.

Core Mechanics

1. Coin Verification Engine

Coins are verified using a highly responsive, non-blocking polling engine via the custom CheckCoin() function. The loop uses a native 30ms debouncing window (millis() - lastCoinDebounceTime > coinDebounceDelay) to prevent ghost electrical signals from being registered as fake coins.

2. Item Selection & Dispensing

Pushing any connected flavor button queues the dispenser. The machine requires exactly 5 PHP of balance to operate. Once triggered, the machine dispenses two items consecutively:

1. The respective continuous rotation servo begins to move (servo.write(90)).
2. The waitForDrop() function actively reads the HX711 scale weight until the dropThreshold is hit or a 3000ms physical timeout triggers.
3. The servo is completely shut off (servo.write(0)) and detached to prevent idle jitter.

3. Non-Blocking Loop Architecture

To prevent CPU lockups where the system might otherwise "ignore" a coin drop:

• CheckCoin() is injected deep inside all software delays (safeDelay()) and while() loops (like waiting for the item to drop onto the scale). No matter what the vending machine is actively doing, incoming coins are safely caught and saved to your balance.
• All hardware selection button reads use HIGH/LOW state detection logic, ensuring the CPU loop never accidentally hangs on a stuck physical button switch.
• The Insufficient Balance screen functions entirely via internal timers rather than hard CPU delay(2000) pauses, keeping exactly 100% responsiveness available to the coin hardware at all times.

Serial Monitor Commands

For testing and debugging without physical hardware interaction, you can use the Serial Monitor (set to 9600 baud rate). Send your commands and press enter.

Command	Action
coin or 5	Simulates inserting a 5 PHP coin (increases balance).
test	Triggers a sequential hardware test of all three servo mechanisms.
1 or barnuts	Simulates selecting the Barnuts flavor.
2 or choco	Simulates selecting the Choco flavor.
3 or milk	Simulates selecting the Milk flavor.

Customization Parameters

• calibration_factor (HX711): Adjust the 2280.0 value in the code to calibrate the specific grams/units your load cell reads.
• coinDebounceDelay: Adjust the 30ms value if your specific electronic coin acceptor pulses slightly faster or slower.
• dropThreshold: Set to 6.0 by default; requires adjustment depending on the actual physical weight registered when a single Polvoron lands on the tray.