# SNAPAY

RFID-based cashless payment system
by Akshit Chaudhary

---

Overview

Snapay is a self-contained RFID cashless payment system built on ESP32. All balance logic runs on the ESP32 using NVS (non-volatile storage). The dashboard is a plain HTML/JS frontend that communicates via MQTT over WebSocket through a HiveMQ cloud broker.

---

Architecture

RC522 Reader
    │
    ▼
ESP32 (brain — NVS balance storage, all logic)
    │
    ▼ MQTT over TLS (port 8883)
HiveMQ Cloud Broker
    ▲
    │ MQTT over WSS (port 8884)
Dashboard (browser — display + input only)

---

Hardware

Wiring

RC522 Pin	ESP32 GPIO
SDA	5
SCK	18
MOSI	23
MISO	19
RST	22
GND	GND
3.3V	3.3V

LED	ESP32 GPIO
Red	12
Green	14

Always use a 220Ω–330Ω resistor in series with each LED.

Users

Token	UID	Name	Account
Card	C0:F5:A1:5F	Akshit Chaudhary	VPAY-0001
Tag	32:73:2E:06	Aviral Chaudhary	VPAY-0002

---

Setup

1. Firmware

1. Open firmware/ in VS Code with PlatformIO installed
2. Edit firmware/src/config.h — fill in your WiFi SSID and password
3. Flash to ESP32:

pio run --target upload

4. Open Serial Monitor at 115200 baud to verify connection

2. Dashboard

No build step needed. Just open dashboard/index.html in any browser.

The dashboard connects to HiveMQ cloud automatically on load.

---

MQTT Topics

Topic	Direction	Payload
rfid/scan	ESP32 → Dashboard	{name, account, balance}
payment/success	ESP32 → Dashboard	{action, name, account, amount, balance}
payment/failure	ESP32 → Dashboard	{action, name, account, reason, balance}
wallet/update	ESP32 → Dashboard	{name, account, balance} or {from, to}
system/status	ESP32 → Dashboard	{status, ip}
wallet/deposit	Dashboard → ESP32	{uid, amount}
wallet/withdraw	Dashboard → ESP32	{uid, amount}
wallet/transfer	Dashboard → ESP32	{amount}

---

Usage

Identify

Tap any card/tag in idle mode → dashboard shows name, account, balance

Deposit

1. Tap card → card activates on dashboard
2. Click Deposit → enter amount → Confirm
3. Tap card again → balance updates

Withdraw

1. Tap card → card activates
2. Click Withdraw → enter amount → Confirm
3. Tap card → balance deducted (or declined if insufficient)

Transfer

1. Tap any card → card activates
2. Click Transfer → enter amount → Confirm
3. Tap sender card
4. Tap receiver card → transfer executes

---

LED Behaviour

Event	Green LED	Red LED
Boot	Both blink once	Both blink once
Card identified (idle)	1x blink	—
Deposit success	2x blink	—
Withdraw success	2x blink	—
Transfer waiting	Slow pulse	—
Transfer success	3x blink	—
Insufficient funds	—	3x blink
Unknown card	—	5x rapid blink

---

Broker

HiveMQ Cloud (free tier)
MQTT port: 8883 · WebSocket port: 8884