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Hardware => Lynx USB DMX Dongle => Topic started by: Ron on February 14, 2010,

Title: Dongle Design Question
Post by: Ron on February 14, 2010,

I have been involved in a discussion in another forum about DMX and a question has come up about how the Lynx dongle works.  I believe I have read that pins 1 and 2 are used for data transmission but that there is no common or ground pun.  Is that true on the Lynx dongle?  If so, what is the reasoning behind it?  I though the DMX standard suggested pin 7 or 8 be connected to ground.

I did find this comment in the RJ45 standards section interesting since I believe LOR uses pins 4 and 5:

The avoidance of pins 4 and 5 helps to prevent equipment damage, if the cabling is accidentally plugged into a single-line public switched telephone network phone jack.

Title: Re: Dongle Design Question
Post by: rrowan on February 14, 2010,

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I have been involved in a discussion in another forum about DMX and a question has come up about how the Lynx dongle works.  I believe I have read that pins 1 and 2 are used for data transmission but that there is no common or ground pun.  Is that true on the Lynx dongle?  If so, what is the reasoning behind it?  I though the DMX standard suggested pin 7 or 8 be connected to ground.

I did find this comment in the RJ45 standards section interesting since I believe LOR uses pins 4 and 5:

The avoidance of pins 4 and 5 helps to prevent equipment damage, if the cabling is accidentally plugged into a single-line public switched telephone network phone jack.

Hi Ron,

I do believe that the dongle follows a DMX-512 standard. http://www.dmx512-online.com/physl.html

I see 3 traces going to the rj-45 connector on the dongle pcb

Rick R.

Title: Re: Dongle Design Question
Post by: Ron on February 14, 2010,

That's good Rick, I was not at a point where I could look at a dongle and just wanted confirmation.  All I could find in the forum was a reference that it was not grounded.

Title: Re: Dongle Design Question
Post by: RJ on February 14, 2010,

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That's good Rick, I was not at a point where I could look at a dongle and just wanted confirmation.  All I could find in the forum was a reference that it was not grounded.

The output device should ground the cable to itself but to prevent ground loops the equipment should not hook to this ground. But not everyone follows this and if it works it does not matter does it. 

RJ

Title: Re: Dongle Design Question
Post by: Ron on February 14, 2010,

Nope, doesn't matter to me because it works.  I was just trying to understand better.

Ron