ESP32 Integration Guide

Overview

The REward kiosk uses ESP32 microcontrollers to detect recycled items and communicate with the API.

Hardware Components

Component	Model	Purpose
Main Controller	ESP32-S (38-pin)	Primary processing
Camera	ESP32-CAM (OV2640)	Dedicated QR Scanner
Display	OLED (ST7789)	User interface (135x240)
Keypad	4x4 Matrix	Manual ID input
Status LED	5mm LED	Visual activity (GPIO 16)
Buzzer	Active Buzzer	Audio feedback (GPIO 17)
Servo	MG995	Sorting mechanism

Wiring Diagram (Core Pins)

ESP32 Pin    Component
---------    ---------
GPIO 16      Status LED
GPIO 17      Audio Buzzer
GPIO 13      Servo PWM
GPIO 26      Inductive Sensor (Metal)
GPIO 25      IR Sensor (Plastic)
GPIO 3, 1    Serial (QR Data from CAM)
GPIO 32-14   Keypad Matrix

API Integration

Authentication

Store API key in ESP32:

const char* API_KEY = "your-secret-api-key";
const char* API_URL = "https://yourdomain.com/api";

Update Status on Boot

void updateKioskStatus(String status) {
    HTTPClient http;
    http.begin(API_URL + "/kiosk/" + KIOSK_ID + "/status");
    http.addHeader("Content-Type", "application/json");
    http.addHeader("X-API-Key", API_KEY);

    String json = "{\"status\":\"" + status + "\"}";
    int code = http.POST(json);
    http.end();
}

Submit Transaction

When user completes recycling:

void submitTransaction(String userId, int plastic, int metal) {
    HTTPClient http;
    http.begin(API_URL + "/kiosk/transaction");
    http.addHeader("Content-Type", "application/json");
    http.addHeader("X-API-Key", API_KEY);

    String json = "{";
    json += "\"kioskId\":\"" + KIOSK_ID + "\",";
    json += "\"userId\":\"" + userId + "\",";
    json += "\"plasticCount\":" + String(plastic) + ",";
    json += "\"metalCount\":" + String(metal);
    json += "}";

    int code = http.POST(json);

    if (code == 200) {
        // Success - display confirmation
        DynamicJsonDocument doc(1024);
        deserializeJson(doc, http.getString());
        int points = doc["transaction"]["pointsEarned"];
        displaySuccess(points);
    }

    http.end();
}

User Flow

1. User scans QR code from app at kiosk
2. Kiosk extracts userId from QR code
3. User deposits items one by one
4. Sensors detect item type (plastic/metal)
5. Servo sorts item to correct bin
6. Count displayed on OLED
7. User presses "Done" button
8. ESP32 calls API to submit transaction
9. User receives push notification with points

QR Code Format

The app generates QR codes containing:

{
    "userId": "abc123",
    "timestamp": 1703019600
}

Sensor Logic

Metal Detection (Inductive)

if (digitalRead(METAL_SENSOR_PIN) == LOW) {
    // Metal detected
    metalCount++;
    activateSorter(METAL_BIN);
}

Plastic Detection (IR)

if (digitalRead(PLASTIC_SENSOR_PIN) == LOW && 
    digitalRead(METAL_SENSOR_PIN) == HIGH) {
    // Plastic detected (not metal)
    plasticCount++;
    activateSorter(PLASTIC_BIN);
}

Safety Considerations

1. Logic Level Shifters - Sensors output 12V, ESP32 is 3.3V
2. Flyback Diodes - Protect against servo motor back-EMF
3. Decoupling Capacitors - Stabilize power for sensors
4. Watchdog Timer - Reset ESP32 if it hangs

Libraries

#include <WiFi.h>
#include <HTTPClient.h>
#include <ArduinoJson.h>
#include <ESP32Servo.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Keypad.h>