doc: add purpose and background
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README.md
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README.md
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these are the hardware design files for **insert project name here**.
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WLED chain is a board for the [WLED](https://kno.wled.ge/) firmware, allowing to power, control, and chain them over Ethernet cables.
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purpose
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=======
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The [WLED](https://kno.wled.ge/) firmware is ideal do control addressable LEDs strip.
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WLED chain is a hardware board for it, matching my usage: robust remotely controlled LED strip based light installations for festivals.
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It allows to:
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- use of the shelf 12-24V power supplies to power the 5V LED strips
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- inter-connect them to form long chains (only connecting the first to externally provided power and data)
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- use cheap Ethernet CAT5E cables to inter-connect them (also over long distances)
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- provide power and data over the Ethernet cables
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- proper 5V LED data signal output (up to three of them)
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usage
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=====
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background
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==========
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origin
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------
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[WLED](https://kno.wled.ge/) is a very good firmware to control addressable LED such as the WS2812b.
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Just get a cheap ESP32 development board, flash WLED using the [web installer](https://install.wled.me/), and of you got.
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I did that very often, and for small projects its fine.
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But for larger projects with multiple devices, you encounter some limitations:
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- you have to separately take care of the power supply: LED strips can draw a lot of current which the development board can not handle
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- remote control using ArtNet over WiFi can be problematic: WiFi routers don't all handle broadcast well, WiFi coverage is not always good, WiFi is jittery
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- providing power to multiple device can be a pain: there is not always a power plug nearby
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this project tries to solve these issues, and since I designed a board, provide even more features
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bus
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---
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The first problem is WiFi:
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- ESP32 operate on 2.4 GHz, a crowded spectrum
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- ESP32 board with built-in antenna have poor reception
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- WiFi router don't always handle broadcast well
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This make the WiFi a poor interface to remotely control LEDs with multiple WLED (using ArtNet or similar) in a real-time manner (low latency and jitter).
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The first solution would be to use Ethernet instead of WiFi.
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This would keep the networking capability.
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ESP32 supports this interface, and the [WT32-ETH01](https://www.seeedstudio.com/Ethernet-module-based-on-ESP32-series-WT32-ETH01-p-4736.html) makes it available.
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But to connect multiple devices you need a Ethernet switch, and run wires from this switch to each device (e.g. is a star topology).
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I wanted to be able to chain the devices, to increase the distance while reducing number of cables and their length.
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You could use the [KSZ8863](https://www.microchip.com/en-us/product/KSZ8863) 3-port Ethernet PHY.
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This can act as Ethernet interface for the ESP32, and built-in switch.
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Now the boards can be chained.
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There is already [schematic](https://github.com/espressif/esp-eth-drivers/tree/master/ksz8863) available, but the support still is beta, and the implementation is complex are not inexpensive.
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I also though about CAN bus.
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This is a very resilient bus, and the ESP32 has an interface for it.
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But WLED does not support it yet, and the host would need a bridge for it.
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Finally I arrived to RS-285.
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It's another differential protocol, often used in the industry because resilient.
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And the implementation is WLED is easy because it's just serial.
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This is when I remembered that DMX512 also uses RS-485.
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And DMX is the de facto standard in the lighting event world.
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Thus interface with is will be very easy and there is a lot of software support.
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The limitation is that it supports only one universe of 512 channels, or 170 RGB LEDs.
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A solution would be to control modes instead of individual LEDs.
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features
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--------
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Here a wish list of features in decreasing order:
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- daisy chain capability (providing data and power)
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- built-in power 5V power supply (input up to 30V)
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- RS-485/DMX512 interface (not isolated)
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- RJ45 port (2x for daisy chain)
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- RJ45 pin header (to solder wires directly)
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- DC barrel jack power input
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- RJ45 power input
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- proper 5V DOUT for WS2812B IC input
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- external WiFi antenna port
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- microphone/line in for sound reactive (use [ESP32-LyraT-Mini](https://docs.espressif.com/projects/esp-adf/en/latest/design-guide/dev-boards/board-esp32-lyrat-mini-v1.2.html) design as reference)
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- [sonoff waterproof enclosure](https://www.sonoffegypt.com/products/sonoff-ip66-waterproof-case) format
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- XLR port (to fit usual DMX512 installations)
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- fully isolated DMX512
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- RDM support (requires adding bias on RS-485, and mostly software support)
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- Lithium battery input and charger (not really the intended use scenario for this device)
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- automotive fuse protection
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- high voltage input (up to 60V, using TPS54560DDAR)
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- USB Power Delivery power input (using IP2721 or FUSB302)
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I'll probably add them with each new version
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other
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-----
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Here a list of other similar LED controllers:
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- [QuinLED-Dig-Quad](https://quinled.info/pre-assembled-quinled-dig-quad/): WLED compatible, but not DMX or power supply
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- [SP201E](aliexpress.com/item/1005005061637017.html): cheap DMX512 LED strip controller, but no WLED, RJ45, or power supply
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- [H807DMX](https://www.aliexpress.com/item/1005005293168050.html): compatible with most LED strips, and has RJ45 DMX512 input, but no WLED or power supply
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