nanoFramework ESP32 RMT Transmitter

Objective

I wanted to connect several some of WS2812 LEDs to my ESP32. I use the nanoFramework as the platform. It turned out that a ready-made solution does not exist, so I had to roll up my sleeve and write it myself.

I studied the solutions of other authors, such as

• Arduino (NeoPixelBus)
• ESP32-NeoPixel-WS2812-RMT

They are use the RMT hardware module of ESP32 as a transmitter of commands for the LED string. So, I need to access to RMT module from C#!

Fortunately, the ESP-IDF provides API for access to this module, it remains only to write a wrapper library for access to this API code from C#.

Solution

According the manual Interop in.NET nanoFramework, I wrote a wrapper that allows a user to control the transmitter of RMT of ESP32.

Using this wrapper, it is possible to write a WS2812 LED control library, however it can be useful on its own, therefore it is separated from the LED control library.

Example

using nanoFramework.Hardware.Esp32.RMT.Tx;      
...      
      
// Register new RTM transmitter on GPIO15   
// It's possible to use any available GPIO     
var rmt_transmitter = Transmitter.Register(GPIO: 15);      
// transmitter configuration      
rmt_transmitter.CarierEnabled = false;      
rmt_transmitter.isSource80MHz = true;      
rmt_transmitter.ClockDivider = 4; // base period 80 MHz / 4 => 20 MHz -> 0.05 us      
rmt_transmitter.IsTransmitIdleEnabled = true;      
rmt_transmitter.TransmitIdleLevel = false;      
      
// create new pulse command for to transmit      
// IDLE  0.5us  1us       1.5 us     2 us             2.5 us	   IDLE..      
//    |----|        |----------|              |------------------|      
// ---|    |--------|          |--------------|                  |------     
var commandlist = new PulseCommandList();      
commandlist	      
    .AddLevel(true, 10)	      
    .AddLevel(false, 20)	      
    .AddLevel(true, 30)	      
    .AddLevel(false, 40)	      
    .AddLevel(true, 50);      
rmt_transmitter.Send(commandlist);      
// destroy transmitter instance and free associated RMT channel      
rmt_transmitter.Dispose();       

Let' see output on GPIO15: