This project is a custom-built liquid dispensing system designed to function as a vending machine for various liquids. It uses 11 Peristaltic Liquid Transfer Pumps (12V) to deliver specific quantities of fluids like juices, syrups, or ingredients in a predefined recipe. A 20×4 I2C LCD display serves as the user interface, controlled by 4 navigation buttons. Additionally, 10 separate buttons trigger specific combinations of liquids, allowing users to choose predefined drink recipes. The entire system is powered by a 12V power supply and controlled via an Arduino Mega. A 16-channel relay module handles activation of the peristaltic pumps.

Components used in Liquid Vending Machine:

System Overview of Liquid Vending Machine:

➤ User Interface:

• 20×4 I2C LCD shows fluid options and amounts.
• 4 Buttons (Next, Back, Enter, Return) allow:
  • Scrolling through liquids A–L.
  • Editing and saving the amount to be dispensed (in ml).

➤ Drink Selection:

• 10 physical buttons, each mapped to a predefined combination of liquids.
• Pressing a button activates related pumps for specific durations based on the quantity set.

➤ Dispensing:

• Each Peristaltic Pump is connected to a relay.
• When activated, a pump runs for a calculated time (based on ml × time/volume calibration).
• After dispensing, the relay turns off automatically.

➤Power Distribution:

• Arduino Mega is powered via USB or separate 9–12V adapter.
• Peristaltic Pumps (12V each) are powered via a 12V adapter connected to the relay module.
• Make sure grounds of Arduino and 12V supply are common/connected.

User Interface Workflow:

Screens:

1. Main Screen: Shows selected fluid (A–L) and its quantity.
2. Edit Mode: Lets user increase/decrease amount and save.

Button Functions:

Fluid Quantity Logic:

• You define how many milliliters (ml) to dispense per fluid.
• The pump runtime is calculated using:
  Duration (ms) = ml × calibration factor (≈67 ms/ml)
• You can edit this for each fluid using the LCD interface.

Drink Selection Workflow:

1. User presses button1 to button10.
2. Each button is mapped to certain liquids.
3. Code saves current millis() time for each active fluid.
4. A Run_Pumps() function checks elapsed time:
   • If within limit: relay ON → pump runs
   • If time exceeded: relay OFF

Circuit Diagram of Liquid Vending Machine:

Arduino Code for Liquid Vending Machine:

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// Set the LCD address to 0x27 for a 16 chars and 2 line display
LiquidCrystal_I2C lcd(0x27, 20, 4);

#define bck_scr 19
#define back 18
#define enter 17
#define nxt_scr 16

// Pin numbers for buttons
const int button1Pin = 15;
const int button2Pin = 14;
const int button3Pin = 2;
const int button4Pin = 3;
const int button5Pin = 4;
const int button6Pin = 5;
const int button7Pin = 6;
const int button8Pin = 7;
const int button9Pin = 8;
const int button10Pin = 9;

// Pin numbers for relay module
const int relayPin1 = 22;
const int relayPin2 = 23;
const int relayPin3 = 24;
const int relayPin4 = 25;
const int relayPin5 = 26;
const int relayPin6 = 27;
const int relayPin7 = 28;
const int relayPin8 = 29;
const int relayPin9 = 30;
const int relayPin10 = 31;
const int relayPin11 = 32;

// Amounts for each liquid in milliliters (ml)
int liquidA = 30;
int liquidB = 40;
int liquidC = 30;
int liquidD = 30;
int liquidE = 30;
int liquidF = 20;
int liquidG = 20;
int liquidI = 30;
int liquidJ = 30;
int liquidK = 30;
int liquidL = 30;

unsigned long pa, pb, pc, pd, pe, pf, pg, pi, pj, pk, pl;

bool La = false, Lb = false, Lc = false, Ld = false, Le = false, Lf = false, Lg = false,
     Li = false, Lj = false, Lk = false, Ll = false;
bool Xa = false, Xb = false, Xc = false, Xd = false, Xe = false, Xf = false, Xg = false,
     Xi = false, Xj = false, Xk = false, Xl = false;
bool flag1 = true, flag2 = true, flag3 = true, flag4 = true, flag5 = true, flag6 = true,
     flag7 = true, flag8 = true, flag9 = true, flag10 = true;

int ON = 0;
int OFF = 1;

int C = 0, scr = 0, E = 0, B = 0, R = 0, L = 0, FN = 0;
bool latch1 = true, latch2 = true, latch3 = true, latch4 = true;

char F[11] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'I', 'J', 'K', 'L' };
int Q[11] = { 30, 40, 30, 30, 30, 20, 20, 30, 30, 30, 30 };

void setup() {
  lcd.begin();
  lcd.clear();
  lcd.backlight();
  lcd.print("YOYO");
  Setup_IO_Pins();
  Calculate();
  update_screen();
}

Future Improvements in Liquid Vending Machine:

• Add Buzzer feedback
• Save Q[] values to EEPROM
• Add coin acceptor or touchscreen
• Add Blynk/IoT support for remote monitoring

Applications of Liquid Vending Machine:

• Mini juice vending stations
• Automatic ingredient dispensing
• Multi-liquid dosing systems
• Chemical or pharmaceutical dosing

Conclusion:

This Liquid Vending Machine using Arduino Mega provides a cost-effective, flexible, and modular platform for dispensing customized combinations of liquids. It uses easily available components and can be tailored to a variety of use-cases like cafes, labs, or home automation. With clearly structured code and hardware, the system is reliable and expandable for future features like touchscreen, mobile app integration, or payment systems.

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