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Angel of Rust

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Posts: 160
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Hi all,

This post is in response to a comment on a thread by Ogremasch (https://artemis.forumchitchat.com/post/update-dmx-basics-guide-9994591?pid=1307071430). Ogremasch noted that a lot of hardware with guides in the forum is hard to find commercially, if at all. My own experience with an off-the-shelf DMX-USB interface was less than stellar. Artemis needs an FTDI chip for the USB interface if using the DMX output that comes directly from the game. That also limits the choices. Some hardware sold with FTDI chips are using counterfeit chips, which don't always work.

Looking at what the USB interface does, and noting people's preference for an RJ45 jack, I have sketched up the following interface design. It needs some testing, but should be up to the task.

The protocols for the RJ45 side are taken from here:
https://en.wikipedia.org/wiki/DMX512#RJ-45_pinout

DMX-USB.png 
DMX-USB SCH.png 
DMX-USB cost.png 

The design is based on my experience building circuits to read the DMX output from Artemis. I also have the parts on-hand, so I am thinking about building one to see how it works.

ogremasch

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I would be interested in testing it out if you make a spare one, let me know and I'll paypal you for the time and materials. 

If I am reading this correctly, this would be a single box that takes USB and Power and gives the user DMX out through RJ45 right? I am not great at reading schematics (yet).

Is there a distance limitation to using RJ45 ( I know that ethernet cables can ony be about 300 feet long for internet use and the max effective length of USB is about 16 feet, I am not sure if DMX has a similar limitation. the likely hood of having a 300 foot cable run is likely very small but I wanted to ask since I am new to the DMX stuff and you have experience with it. I have also heard of people in the Forums having trouble with their DMX that may be linked to the USB being too long. I have limited my DMX USB cable to 3 feet to avoid that problem which means I will need to apply the length to the DMX side of the board which leads me to needing to know if there is a max limit my server PC can be away from my bridge and still effectively control lights with relatively little or no perceivable lag. 

I look forward seeing more in this thread as the project develops. 

 
Angel of Rust

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Posts: 160
Reply with quote  #3 
Quote:
Originally Posted by ogremasch
I would be interested in testing it out if you make a spare one, let me know and I'll paypal you for the time and materials. 

If I am reading this correctly, this would be a single box that takes USB and Power and gives the user DMX out through RJ45 right? I am not great at reading schematics (yet).

 



I was originally just thinking about a replacement for the basic USB-to-DMX interface using an RJ45 jack for the DMX part. Having power on there seems like a good idea, so I added it:

USB DMX B.png   
DMX USB B SCH.png 

I put a 2.1 mm DC barrel jack on there so power can be provided at whatever voltage needed. Per Power-Over-Ethernet convention, I have assigned the RJ45 pins as follows:
1: D+ (data)
2: D- (data)
4 and 5: +Volt
7 and 8: ground

I plan to make one in the near future. I'll let you know how it goes.


Quote:
Originally Posted by ogremasch


Is there a distance limitation to using RJ45 ( I know that ethernet cables can ony be about 300 feet long for internet use and the max effective length of USB is about 16 feet, I am not sure if DMX has a similar limitation. the likely hood of having a 300 foot cable run is likely very small but I wanted to ask since I am new to the DMX stuff and you have experience with it. I have also heard of people in the Forums having trouble with their DMX that may be linked to the USB being too long. I have limited my DMX USB cable to 3 feet to avoid that problem which means I will need to apply the length to the DMX side of the board which leads me to needing to know if there is a max limit my server PC can be away from my bridge and still effectively control lights with relatively little or no perceivable lag. 

I look forward seeing more in this thread as the project develops. 

 


300 feet sounds about right. Because DMX uses RS485 protocol, which is a differential pair for signal, typically in twisted pair wire (such as cat 5 cable), it can go longer than any of us are likely to use up. As far as I can tell, it doesn't generate a lot of errors.

USB has a pretty short length limitation as you noted. Shorter is better. Otherwise, boosters are needed.



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