01 Overview

The RMT LED strip example demonstrates how to drive WS2812-class single-wire protocol strips using the ESP32's RMT peripheral. RMT generates precise timing waveforms in hardware, freeing the CPU, making it ideal for large numbers of LEDs.

LED strips are commonly used for status rings, accent lighting, decorative lights, and any application requiring multi-color, programmable, dynamic effects.

This example is not for simple single-color GPIO lamps; use Blink or LEDC for those. It is also not for high refresh rates or complex protocols like SPI strips.

WS2812 uses a single-wire return-to-zero protocol with 24-bit GRB data per LED, requiring strict timing. RMT handles this easily.

Power and ground design are critical when driving strips; poor design leads to flicker, color errors, and other issues.

During RF certification, the strip itself can become an EMI source, so attention to suppression is necessary.

02 Hardware

• Strip power: Strips often need 5V; verify if LEDs are 3.3V tolerant, otherwise level shift data line.
• Level shifting: If LEDs are not 3.3V tolerant, add a level shifter (e.g., 74HCT245) or use 3.3V-tolerant LEDs.
• Decoupling: Add 100-1000µF electrolytic capacitor at strip power input and 0.1µF ceramic near the strip.
• Grounding: Return current and ground plane decide flicker; ensure adequate trace width and low impedance.
• Connectors: Common JST or dupont; check current rating.
• EMI: Strips are interference sources in RF tests; may need ferrite beads or shielding.
• Layout: Keep data lines short and away from power lines to avoid crosstalk.

03 Software flow

1. Configure RMT channel and GPIO, set clock source and divider.

2. Initialize strip driver, allocate GRB buffer (size = number of LEDs × 3).

3. Fill buffer with color values for each LED.

4. Call refresh function; RMT sends waveform automatically.

5. Avoid recomputing colors in ISR; update buffer first, then trigger refresh.

6. For dynamic effects, update colors in main loop and refresh.

7. Error handling: check RMT transmission completion, retry if needed.

04 Core points

• Power, not code, usually causes sparkle. Insufficient voltage or poor grounding leads to color errors or flicker.
• Timing margin: Different LEDs have slight timing variations; configure RMT with margin.
• Don't copy across chips: RMT peripheral differs slightly across ESP32 series; refer to respective TRM.
• Custom work: effects, level shift, layout, power design.
• Thermal: High current over long periods may heat up; consider heat dissipation.