Expanding RPI-28D+

Matt430

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Hi,

I am just getting started in blinky lights and looking at starting my first light show and have an existing Raspberry Pi 4B. I plan to use a RPI-28D+ to get me started with the 2 WS2811 channel outputs with FPP loaded onboard.

I have read that you can extend the number of channels through the RJ45 port using DMX and FPP. Is this possible with the RJ45 port on the RPI-28D+? Could you connect into a HE123-EX2 4 Channel RJ45 breakout board and extend the number of pixels supported by the Raspberry Pi and RPI-28D+ combo? If this is possible does is also require the paid license for FPP? In my case the extension would sit right next to the Pi with the purpose of providing more channels for pixels.

I am also slightly confused around the HE123-4T different transmitter and HE123-RX2 differential receiver. Are these what are used to extend the number of pixels on controllers?

Any help would be greatly appreciated!

Thanks :)
 

Skymaster

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No, you can't use the DMX port, however you can use the WS2801 port.
If you license FPP (paid) for 4 outputs, and enable the DPIPixels code, you can address four outputs total; the two regular outputs, and then the "Clock" and "Data" lines on the WS2801 become two independent WS2811 outputs.

The DMX/RJ45 internally connects to the serial port ttyAMA0, so this can only be used for serial data, not pixel data.
You could, however, use a DMX pixel controller, but you can only get 170 pixels out of the 510 (512) channels in DMX.
 
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Skymaster

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I am also slightly confused around the HE123-4T different transmitter and HE123-RX2 differential receiver. Are these what are used to extend the number of pixels on controllers?
Not the number of pixels but the distance.
WS281x data can only go a certain distance before it is affected by the cable capacitance and interference to the point where the pixels cannot understand it. This can be anywhere from 2-10m depending on the cable, the controller and the pixels and how the interact.

But converting it from a "single ended" signal to a differential signal (HE123-4T does this) - it can be sent across in what's called a balanced pair - over CAT5 - this is virtually immune to noise. You can then crazy distances - over 70+ metres- before converting the signal back to the single-ended signal (HE123-RX2 does this) - which the pixels then understand.
You still need to worry about getting power to your pixels with this method though. PSU would be near pixels.
 
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Matt430

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Thanks Skymaster,

Makes sense now :) with the difference between the 3, sounds like the best bet to get started is to use the RPI-28D+ and if needed purchase a license key to unlock the additional 2 outputs through the 4 pin connector.

I vaguely remember reading that this may cause the audio output to not work if a radio transmitter is being used with the show due to the pins used on the Pi to add the additional outputs? But we can get around this by using audio through usb?

In the future if more pixel control is needed it sounds like you could upgrade the controller and then keep the Pi to use as the show player.
 
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Skymaster

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I vaguely remember reading that this may cause the audio output to not work if a radio transmitter is being used with the show due to the pins used on the Pi to add the additional outputs? But we can get around this by using audio through usb?
If you use the 2 channel mode with the Free pixel output code, then the onboard sound doesn't work, as the PWM pins are used for the pixel output.
But, if you license FPP to use the DPI Pixels code, you can then run all four outputs as well as get the onboard sound back, as it uses a different way of getting the pixel data out.

That being said, the audio on the Pi is pretty ordinary and most opt for a USB Sound device (most commonly the SB Play 3! unit) as the output device - even when not running pixels from the player.

In the future if more pixel control is needed it sounds like you could upgrade the controller and then keep the Pi to use as the show player.
Absolutely - it's a great way to start out to learn how it all pieces together, and then have it as an upgrade path down the track.
 
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