Artnet ESP32 library

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This library is a take on the usage of the Artnet protocol to display leds and record on a SD using an esp32 when dealing with a large number of leds (> 800). This library will allow you to:

• Live play of Artnet stream
• Record the stream on a SD card
• Replay the recorded file

Couple of considerations when using Artnet

Receiving Artnet universes

The Artnet protocol is intensively used in light shows and numerous lighting software have the capability to output the data using the artnet protocol. The artnet protocol uses the concept of universe. A universe is a subset of the information you want to send. Each universe can contain 512 bytes of data + the header information. The Artnet protocol uses UDP internet protocol which does not provided receive/check/resend capabilities which means that when the artnet server sends out an artnet packet it doesn't wait for any acknowledgment before sending the next one. As a consequence a packet not intercepted by the artnet reciever is LOST.

If you send RGB pixel informatiion you can have maximum 512/3 =170 pixels per universes. Hence if your project contains 1800 leds you would need at least 11 universes (10 full universes and the last one with 100 pixels).

Now if you have an artnet broadcast at 25fps (each frame is 40ms appart) each universe will be maximum 4/11=0.36ms appart. Hence speed is critical in gathering the universes without losing any artnet packet.

Using the universes

For most users the use of artnet is the following :

Gather the artnet universes ->move the data in the leds buffer-> display the leds
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The WS281X are one of the most leds used. This led are cheap and easy to use. But they are clockless leds which means that the speed to 'upload' the data in them is fixed and in that case the 'upload speed' is 800kHz which means that to transfer the data for one led it requires 3x8bits/800.000=30us. Hence in our case 1800 x 30us=54ms.

If using a sequentiel flow when displaying you will lose 2 artnet frames (the first one totally and part of the second frame => not usable) It is necessary to reduce the time needed to display the leds => split your leds over several PINS. If you're using the Fastled library it will divide the time by the number of pins used. Hence if you are using 4 pins (450 leds per pin) the display time will be 13.5ms hence losing only one frame.

it will work but the display will not be smooth.

Recording/Replaying the universes

Writing/Reading to/from a SD card is also a time consuming process which could last longer than time betwwen two frames. The frames are not always sent with an exact timing depending on the artnet sending program. To be able to replay it with the most accurate timing the program will store in microseconds the delay between frames to be used during replay.

Solutions implemented in this library

Artnet universe processing speed

To process the wifi packet and the artnet packet this library uses the barebone socket functions to reduce the processing. It gather all the universes at once removing all unnessary code out of this function

Using the second core

If we use a pure sequential workflow the program will not be listening to artnet packet while displaying the leds. Hence this library implements the use of the two cores of the ESP32 : one core is processing the data while the other one is displaying/recording the data.

Take away

When using artnet streaming, You need to take into account the timing issues :

• Do not try to get artnet to broadcast at too much fps otherwise you will have too many lost frames in artnet
• Dispatch your leds over several pins to lower the refresh time of your display
• Do not hesitate to buy a good SD card to have a good write/read speed

Library usage

The artnet object

#include "ArnetESP32.h"
ArtnetESP32 artnet; 

Main functions

void begin(int NUM_LEDS,int UNIVERSE_SIZE)

This function starts the artnet objects.

• NUM_LEDS is the total number of leds of your setup
• UNIVERSE_SIZE is the size of you universes in pixels Based on these two numbers the program will calculate the number of needed universes

void setLedsBuffer(uint_8t*) buffer)

This function will set the buffer that will store the frame retrieved from readFrame() readNextFrameAndWait() and readFrameRecord()

uint16_t readFrame()

This function will receive one frame or all the needed universes.

• Will exit with "Time out" after 1s of inactivity
• Will return 1 if a frame has been received otherwise 0 when timeouting

void startArtnetrecord(File File)

This function sets up and starts what is needed to record the frames onto the file.

uint16_t readFrameRecord()

This function receives a frame a store it in the file. It also store the delay between frames

• Will exit with "Time out" after 1s of inactivity
• Will return 1 if a frame has been received otherwise 0 when timeouting

void stopArtnetRecord()

This function is mandatory to call to end the recording it will also close the file

bool readNextFrameAndWait(File file)

This function reads a frame from the file and waits the necessary time. it returns true if the file has not be entirely read else it will returns false

The callback functions

When uploading a frame, recording a frame or reading a frame from SD a callback function can be setup

void setFrameCallback(void (*fptr)())

This function set the function that will be called when a frame will be received using the readFrame() function

void setframeRecordCallback(void (*fptr)())

This function set the function that will be called when a frame will be received using the readFrameRecord() function

void setreadFromSDCallback(void (*fptr)())

This function set the function that will be called when a frame will be received using the readNextFrameAndWait(File file) function

Examples

Each example shows how to uses these functions :

exampleArtnet

This is the example to receive and display artnet

SD-Arnet

This is the example to record artnet

readSD

This is the example to replay the recorded artnet file