⚡ Charge Controllers and Protection Circuits

A charge controller prevents battery over-charge and over-discharge, essential for long battery life.

📊 Charge Controller Types:

🔌 TP4056 Wiring (Most common for IoT):

TP4056 Module Connections:
IN+  → Solar Panel Positive (6V)
IN-  → Solar Panel Negative
BAT+ → 18650 Battery Positive
BAT- → 18650 Battery Negative
OUT+ → ESP32 Vin (or 3.3V regulator)
OUT- → ESP32 GND

Features:
- Charging current: 1A (adjustable)
- Over-charge protection: 4.2V cutoff
- Over-discharge protection: 2.5V cutoff
- Charging status LEDs: Red (charging), Blue (full)
    

📖 Battery Voltage Monitoring:

#define BATTERY_PIN 34

float readBatteryVoltage() {
    int raw = analogRead(BATTERY_PIN);
    // Voltage divider: 100k/100k = 2x divider
    float voltage = (raw / 4095.0) * 3.3 * 2;
    return voltage;
}

void checkBattery() {
    float vbat = readBatteryVoltage();
    
    if (vbat < 3.2) {
        Serial.println("⚠️ Battery LOW! (3.2V)");
    } else if (vbat < 3.0) {
        Serial.println("⚠️ Battery CRITICAL! (3.0V)");
    } else if (vbat > 4.2) {
        Serial.println("⚠️ Battery OVER VOLTAGE!");
    } else {
        Serial.printf("Battery: %.2fV\n", vbat);
    }
    
    // Battery percentage (Li-ion approximate)
    int percent = map(vbat, 3.0, 4.2, 0, 100);
    percent = constrain(percent, 0, 100);
}