Arduino-Based HHO Controller: Smart PWM with Temperature Monitoring

Why a Smart Controller Outperforms Basic PWM

A basic PWM controller runs at a fixed duty cycle regardless of cell temperature, alternator voltage, or engine RPM. A smart Arduino controller responds to changing conditions in real time: reduces duty cycle when temperature rises, adjusts for alternator voltage variation, and can correlate HHO output to engine load via RPM signal.

Required Components

• Arduino Nano or Uno ($8–$15)
• IRF540 MOSFET or a 30A solid-state relay ($5–$15)
• DS18B20 temperature sensor ($3)
• Voltage divider resistors for 12V → 5V sensing
• OLED 128×64 display ($5)
• LM2596 buck converter for 5V Arduino supply ($3)

Core Code Logic

The Arduino reads temperature (via DS18B20) and voltage (via voltage divider on analog pin) every 500ms. If temperature exceeds 45°C, reduce PWM duty cycle by 5%. If voltage exceeds 14.5V, reduce duty cycle proportionally. Display current duty cycle, temperature, and voltage on the OLED. Target current draw is maintained within ±0.5A through PID feedback if current sensing is added.

RPM Integration

Reading the tachometer signal (from the ignition coil or OBD-II real-time RPM via a Bluetooth OBD adapter sending serial data) lets the Arduino increase HHO output at higher engine RPMs (highway) and reduce it at idle — optimizing for actual combustion need rather than running at constant output.

Safety Features

Code must include: emergency off if temperature exceeds 65°C (safety cutoff), watchdog timer that shuts off HHO if the Arduino crashes, and startup delay (30-second warm-up before enabling HHO to allow engine to start normally).