Radiation Analysis: Arduino UV Index Meter

A generic light sensor (LDR) detects visible light; it is completely blind to dangerous solar radiation. The Arduino UV Index Meter utilizes specialized gallium nitride photodiodes to measure the horrific, invisible UV-A and UV-B rays blasting from the sun, mathematically outputting the true World Health Organization (WHO) safety index directly onto a high-contrast screen.

The Physics of the ML8511 UV Sensor

The GY-ML8511 UV Sensor Module is one of the most sensitive analog instruments used in Arduino engineering.

1. The sensor outputs an analog voltage directly related to the massive intensity of the invisible 280-390nm light spectrum (Targeting the deadliest sunburn-causing rays).
2. The math is not 0-1023. The sensor has a strict datasheet curve: 1 Volt = 0 UV Index 2.8 Volts = 15 UV Index (Absolute, blistering desert sun).
3. The 3.3V Calibration Trap: The biggest mistake programmers make is referencing the Uno's default 5V line. The ML8511 requires exactly 3.3V. You must physically run a jumper from the Arduino's 3.3V pin straight back into the A1 analog-reference pin to act as a mathematical control anchor!

Floating Point Output and Map Function

Because the analog data is linear but compressed into a tiny voltage scale (1.0V to 2.8V), standard integer math fails.

• You must create a custom mapfloat() function! The standard C++ map() function only returns whole numbers (like Index: 4).
• We want precise decimal analysis (Index: 4.8! Alert: Skin damage in 12 minutes!).

float mapfloat(float x, float in_min, float in_max, float out_min, float out_max) {
  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

• The code calculates the decimal and shoots the warning directly onto an I2C OLED SSD1306 Display.

Solar Observation Hardware

• Arduino Uno/Nano.
• ML8511 or VEML6070 I2C UV Light Sensor Module.
• 0.96" I2C OLED or 16x2 LCD Display.
• A battery-powered 3D printed enclosure allowing you to carry the sensor to the beach or point it directly at the sun! (Warning: Place a clear piece of specific quartz glass over the enclosure hole. Standard plastic acrylic or window-glass blocks 90% of UV rays and will completely blind the sensor!)