DMX / XLR & Cables

[timsabre]

It's strange to think of now, but at that time there were no cheap Chinese DMX lights. A number of UK manufacturers were the first to bring out cheap DMX equipment. 5 pin XLR cabling was very rare and the connectors very expensive - far too much for cheap products

[Jivemaster]

NJD used TRS jacks! With the advantage that the switching sockets automatically terminated the line if there was no ongoing lead fitted.

[timsabre]

Abstract used jacks too on their first DMX scans.

[sunray]

I worked for a small nightclub Sound and Light company for a year, (they were heavily tied to Martin) and that was my initial introduction to 'DMX' style operations. My role was limited to hanging, addressing, pointing and servicing. I hardly touched any form of programming. The cables and terminators supplied by Martin were 75 ohm and every one in the business reckoned they were incompatible with DMX. We knew better as the software and pc cards were the same for both formats. initially we only touched Martin products but started upgrading existing systems with a Martin pc card and software and adding Martin fittings into the existing DMX runs without using any form of phase reversals as it was all done in the drivers.

[Gareth A]

Also Jem / Martin Glaciators are STILL sold with 3 pin connecters on the control panel!

[timsabre]

All recent Jem machines have 3 and 5. Glaciator is quite an old model...

[ThomJ]

The 5 pin connectors were initially used as there was to be an additional control feature on the pins 4 & 5 this didn't take off and people use the 5 pin to differentiate between 3 pin signal (mic) cable and DMX cable.

[sunray]

The RS485 format can be used as 1 pair or 2 pair system, 2 pair is usually used for a point to point application to increase speed but it can also in a multipoint with the master being the only one to transmit on pair 1 and receive on pair 2. I can't remember the make but we installed some active loudspeakers which were controlled this way with feedback to confirm the settings.

[timsabre]

No, point to point requiring 2 pairs is RS422. RS485 (DMX) is always multi-drop with bidirectional use of a single pair.

[sunray]

No, point to point requiring 2 pairs is RS422. RS485 (DMX) is always multi-drop with bidirectional use of a single pair.

Correct RS422 is designed as point to point as is RS232 but the spec for both gives the maximum no of receivers that that can be hung on a line.

RS485 can also be used as point to point or 2 pair multi with one device being designated master such that master always has priority, a one pair system, like DMX, can get blocked by a station in permanent transmit.

Mid 80's I could have quoted hook line and sinker on the spec's and created workarounds to make them work outside their spec's or usual modus operandi. but 30 years on most of it left my grey cells through lack of use.

More to the point many manufacturers tried to cut corners with a system that didn't quite meet the spec but still worked and sometimes making such systems work together created much head scratching especially RS232 where +- 3V or even 2V were not too uncommon.<br />Certainly one of the plethora of computer terminal systems used by BT over the years used a 2 pair RS485 format and we regularly added additional terminals and printers using only the RX pair so traffic could be monitored in additional locations.

 

From:  http://www.windmill.co.uk/rs485.html:   When instruments are described as having an RS485 interface this tells you nothing for sure about the signals being transmitted. Usually though only the Transmit Data (TX) and Receive Data (RX) of a normal serial port are converted to RS485 or RS422. The other signals of the serial port are not used. Three arrangements are commonplace: Write only, 4-wire (full duplex) and 2-wire (half duplex).

 

Edit: That site is worth a read, it explains thing in a light way