Automatic Vending Machine Prototype with Coin Acceptor and Product Selection

Small shops, hostel canteens and college snack counters usually sell through an attendant: the buyer asks, the seller picks the item, and change is counted by hand. That works while the counter is staffed, but it stops during breaks, after hours, and whenever the attendant steps away, and every sale depends on someone being present to take money and hand over stock. A coin-operated vending prototype removes the attendant from that loop. The buyer inserts coins, watches the balance grow on a display, presses the button for the product they want, and collects it from a pickup tray — the same transaction a staffed counter performs, handled by a coin acceptor, a controller, and a spiral dispenser. For an electronics student, the value of the build is that each stage is visible and testable: coin validation, pulse counting, balance arithmetic, price comparison, and motor timing all happen in hardware and code the student can probe.

A sale begins when a buyer drops a coin into the acceptor slot and ends when the chosen product lands in the pickup tray, with the controller tracking money and stock at every step in between. The acceptor first checks the coin by size, thickness and material signature, and only a coin it recognises produces pulses; anything else falls through to the reject path without adding to the balance. The controller counts those pulses into a rupee balance and updates the LCD, so the buyer watches the total grow coin by coin. When a product button is pressed, the controller compares the balance with that lane's price: if the balance is short, nothing moves and the display shows the shortfall; if the balance covers the price, the lane motor turns its coil one full rotation, one item drops, the price is subtracted, and the remaining balance stays displayed for the next selection or a coin return.

1. The buyer inserts a coin into the CH-926 acceptor, which validates it by diameter, thickness and material signature and rejects unrecognised coins to the return path.
2. For each accepted coin, the acceptor sends a pulse train to the Arduino Uno, which adds the coin's programmed value (Rs 1, Rs 2, Rs 5 or Rs 10) to the running balance.
3. The 16x2 LCD updates after every coin to show the current balance, and the four selection buttons stay armed for lanes A1, A2, B1 and B2.
4. The buyer presses one product button; the controller reads the price stored for that lane and compares it with the balance.
5. If the balance is short, no motor runs and the LCD shows INSUFFICIENT BALANCE with the shortfall, so the buyer can insert more coins.
6. If the balance covers the price, the controller drives that lane's DC gear motor through the L298N driver for one full coil rotation, dropping exactly one item into the pickup tray.
7. The controller subtracts the price from the balance, shows the remaining balance on the LCD, and the buyer collects the item or presses another product button or the coin-return button.

Tech stack:

• Arduino Uno · ATmega328P
• CH-926 multi-coin acceptor
• 16x2 LCD display
• DC gear motors · L298N driver
• Spiral dispenser coils
• Push-button selection panel
• 12 V DC power supply
• Arduino IDE · C++

The build is organised around four capabilities that together complete one unattended sale. Multi-coin acceptance lets the buyer pay with more than one denomination, because the programmable acceptor identifies each coin and reports it as pulses the controller can count. A live balance display keeps the transaction honest: the LCD shows the running total after every coin and the price of the selected product, so the buyer always knows where they stand. Spiral-lane dispensing turns a button press into a delivered product, with one motor per lane rotating its coil exactly one turn so a single item drops. Balance and refund handling closes the loop safely: an underpaid selection is refused without dispensing, and the remaining balance stays on the display for the next selection or a coin-return press, with the LCD confirming each step along the way.

• [Multi-coin acceptance] A programmable CH-926 acceptor identifies up to 6 coin types (datasheet) and reports each accepted coin as a pulse train, so the controller can add Rs 1, Rs 2, Rs 5 and Rs 10 coins into one running balance.
• [Live balance display] A 16x2 LCD shows the inserted balance after every coin, the price of the selected lane, and messages such as INSERT COIN, INSUFFICIENT BALANCE, and DISPENSING, so the buyer never guesses the machine state.
• [Four spiral dispenser lanes] Four labelled lanes (A1, A2, B1, B2) each hold one product behind a clear panel, and each coil is driven by its own DC gear motor through an L298N driver for independent dispensing.
• [One-turn dispense control] The controller runs the selected lane motor for one full coil rotation (design behaviour), so exactly one item advances and drops into the pickup tray per paid selection.
• [Insufficient-balance protection] A selection that costs more than the inserted balance is refused without rotating any coil, and the display shows the shortfall so the buyer can insert more coins.
• [Coin-return button — transaction reset] A return button ends the transaction, shows the balance being cleared on the display, and resets the balance to zero for the next buyer; it does not dispense coins as change (see Limitations).
• [Builder note — acceptor calibration] During calibration, a Rs 10 coin was first rejected because its pulse count overlapped the stored Rs 5 sample; re-teaching the acceptor with 20 sample insertions of each denomination, as the acceptor manual prescribes, separated the two coins cleanly. Budget calibration time for every denomination you plan to accept.
• [Builder note — spiral jam lesson] A packet wider than the coil pitch wedges between turns instead of advancing; keep packet width below the coil pitch and test each lane with its actual product before the demonstration, not with an empty coil.

• Complete vending machine prototype: cabinet, clear front panel, 4 spiral lanes, coin acceptor, display and selection panel
• Arduino Uno controller with the full coin-counting, balance and dispense firmware
• L298N motor driver board and 4 DC gear motors wired to the spiral coils
• 12 V DC power supply with step-down regulation for the logic circuits
• Project report PDF covering problem, coin validation, balance logic, dispensing mechanism, testing and limitations
• PPT presentation for review
• Viva Q&A preparation document covering coin acceptors, pulse counting, motor drivers and embedded control flow

To request this project on a quotation basis, message on WhatsApp with the scope needed: 2-lane bench demo, the full 4-lane cabinet, or the full build with documentation. The quotation covers the agreed scope, the build is prepared to order, and delivery timing is discussed on WhatsApp once the scope and any customisation are confirmed. No fixed price is quoted on this page, and no delivery date is promised before that discussion.