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ESP32 RMT Guide: Infrared, WS2812 LED Strips and Pitfalls
RMT is the most underrated ESP32 peripheral: IR remotes, WS2812 strips and one-wire sensors all depend on it. Channels, resolution and the Wi-Fi interference problem.
What RMT is for
RMT (Remote Control) was designed for infrared remotes, but really it is a programmable precision waveform generator. It emits arbitrary high/low sequences at ~12.5 ns resolution and does so without the CPU — you write the data to memory and the hardware plays it out while the core does something else.
Besides IR it is now the standard way to drive:
- WS2812 / SK6812 one-wire RGB strips (by far the most common use today)
- DHT11 / DHT22 one-wire sensors (both RX and TX)
- Stepper-motor pulse trains and other custom single-wire protocols
Channels and resolution
| Item | Original ESP32 | Note |
|---|---|---|
| Channels | 8 | Shared between TX and RX |
| Clock source | 80 MHz APB | ≈12.5 ns per tick |
| S2 / S3 / C3 / C6 / H2 / P4 | Verify against official docs (counts differ; C3 has notably fewer) | |
Check the documentation for channel counts: they vary a lot between chips, so only the original ESP32 figures are stated here.
The big one: Wi-Fi makes your LEDs flicker
WS2812 timing is tight (a "0" bit is about 0.35 µs high). While Wi-Fi is active the radio briefly stalls the bus and delays the interrupt that refills RMT memory, stretching a bit — which shows up as randomly wrong colours or a flickering strip.
Common mitigations:
- Send the strip in small chunks to shorten each transfer.
- Bit-bang the waveform over SPI instead — SPI has DMA and copes far better.
- Lower the refresh rate to dodge Wi-Fi bursts.
- Disable Wi-Fi modem sleep to reduce sudden latency spikes.
Other gotchas
- Symbol memory per channel is limited: long strips must be sent in chunks or via loop mode.
- RMT is not pin-picky — it runs through the GPIO matrix — but the input-only GPIO 34–39 cannot be used.
- IR transmit needs a transistor to drive the LED; the IO pin cannot source enough current.
- IR receiver modules (VS1838B and friends) output inverted logic: low means carrier present.
Data verified：2026-10-20 · Cross-checked against Espressif documentation. Anything that varies between chips or ESP-IDF releases is marked rather than guessed.
Official peripheral docs →
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