Experimental Arduino SPWM Code Generator

SPWM on Arduino (Using analogWrite)

Sine Pulse Width Modulation (SPWM) is a technique to generate an approximate sinusoidal AC waveform from a DC supply using PWM. On standard Arduino boards (like Uno, Nano, Mega), the `analogWrite()` function is the simplest way to generate PWM signals.

This code generates a unipolar SPWM signal, meaning the duty cycle varies from 0 (off) to 255 (full on). To generate a full AC waveform (bipolar), this signal would typically drive one leg of an H-bridge, with a complementary or phase-shifted signal driving the other leg.

Key Parameters:

• Modulation Index (Ma): Controls the amplitude of the output sine wave. A higher `Ma` (up to 1.0) results in a larger output voltage.
• Output Sine Wave Frequency: The desired frequency of the generated AC waveform (e.g., 50 Hz or 60 Hz). This is achieved by updating the PWM duty cycle from the lookup table at a specific rate.
• Number of Samples per Sine Cycle: Determines the number of discrete duty cycle values in the sine lookup table for one full cycle. More samples lead to a smoother sine wave, but consume more memory.
• PWM Output GPIO Pin: The digital pin on the Arduino where the PWM signal will be output. On Uno/Nano, typical PWM pins are 3, 5, 6, 9, 10, 11.

Limitations & Considerations for `analogWrite()`:

• PWM Resolution: `analogWrite()` on most Arduinos (like Uno/Nano) operates at a fixed **8-bit resolution (0-255)**. You cannot change this in software using `analogWrite()`.
• PWM Carrier Frequency: The underlying PWM carrier frequency of `analogWrite()` is also fixed by the Arduino hardware timers. It’s typically around **490 Hz** for pins 5, 6, 9, 10, 11, and 3, and around **980 Hz** for pins 3 and 11 (on Uno/Nano). This cannot be changed with `analogWrite()`.
• Smoother Output: For a smoother sinusoidal output, you generally want a high PWM carrier frequency (much higher than your sine frequency) and a high number of samples. While this tool lets you set samples, the fixed carrier frequency of `analogWrite()` may limit the quality of the sine wave, especially at higher output sine frequencies.
• Advanced PWM: For higher resolution PWM, custom carrier frequencies, or more complex control (like dead-time insertion for H-bridges), direct manipulation of AVR microcontroller timers and registers is required. This code does not cover those advanced techniques.

Note: This code provides a basic SPWM implementation. For real-world applications, especially high-power inverters, consider the limitations of `analogWrite()` and explore advanced timer programming if needed.