Panduan ESP12E 12V Battery Monitor

Apa Projek Ni

Monitor bateri 12V (macam bateri kereta atau solar setup) guna ESP12E. Baca voltage, display kat OLED, hantar data ke server. Macam fuel gauge tapi untuk bateri.

Components

ESP12E / NodeMCU
Voltage divider (25V max → 3.3V for ADC)
OLED SSD1306 128×64
12V battery

Voltage Divider

ESP8266 ADC max 3.3V (actually 1V internal, NodeMCU ada built-in divider to 3.3V). Untuk baca 12V battery, kena scale down lagi.

Guna resistor divider: R1 = 100kΩ, R2 = 33kΩ

Vout = Vin × R2 / (R1 + R2)
Vout = 12V × 33k / (100k + 33k) = 2.98V  ← safe for ADC

Max measurable: 3.3V × (133k / 33k) = 13.3V

Covers full 12V battery range (10.5V empty → 12.8V full).

Wiring

From	To
Battery +	R1 (100kΩ) → junction → R2 (33kΩ) → GND
Junction (between R1 & R2)	A0
Battery –	ESP GND (common ground!)
OLED SDA	D2
OLED SCL	D1

⚠️ Common ground penting — battery GND dan ESP GND kena sama. Kalau tak, reading jadi nonsense.

Code

#include <Wire.h>
#include <Adafruit_SSD1306.h>

#define ADC_PIN A0
#define R1 100000.0
#define R2 33000.0
#define VREF 3.3

Adafruit_SSD1306 display(128, 64, &Wire, -1);

void setup() {
  Serial.begin(115200);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
}

void loop() {
  int raw = analogRead(ADC_PIN);
  float vADC = raw * (VREF / 1023.0);
  float vBattery = vADC * ((R1 + R2) / R2);
  
  // Battery percentage (rough estimate for lead-acid)
  // 10.5V = 0%, 12.8V = 100%
  float pct = (vBattery - 10.5) / (12.8 - 10.5) * 100.0;
  pct = constrain(pct, 0, 100);
  
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(0, 0);
  display.printf("%.1fV", vBattery);
  display.setTextSize(1);
  display.setCursor(0, 30);
  display.printf("%.0f%%", pct);
  display.display();
  
  Serial.printf("Battery: %.2fV (%.0f%%)\n", vBattery, pct);
  delay(5000);
}

Calibration

Resistor tolerance affect accuracy. Untuk calibrate:

Ukur battery voltage dengan multimeter
Compare dengan reading dari ESP
Adjust ratio dalam code: float calibration = actual_voltage / esp_reading;

Battery Voltage Reference (12V Lead-Acid)

Voltage	State
12.7V+	100% (full)
12.4V	75%
12.2V	50%
12.0V	25%
11.8V	~0% (discharge soon)
10.5V	Dead — stop discharging!

Notes

Add 100nF capacitor between A0 and GND untuk stabilize reading
Take average of 10 readings untuk reduce noise
Kalau nak monitor over time, push data ke InfluxDB/MQTT macam projek sensor udara
For LiPo batteries, voltage range different — adjust accordingly