USB to XLR (DMX) Query...

[jexjexjex]

Hi Troops,

 

Not sure if this should be here or in the "Lighting" section - Mods please feel free to move if necessary.

 

I've been handed a query relating to my day job and some of you will be able to answer this.

 

I'm wondering if anyone knows the "pin-outs" for a USB connector?

 

The issue is that I need a USB to 3 pin XLR cable for connecting a standard Windows tablet (USB) to a traffic data collector (XLR).

 

The company that make the data collectors want £60 each for replacement or spare cables but, as we know, there are loads of cheap ones available on sites like Fleabay and Amazon for DMX purposes.

 

The only issue that I can see is how the pins on the XLR end will be configured and that's easy to solve if necesary.

 

We're going to get one and I'll compare the two on my workbench after Christmas, but I'm really looking for some pointers on what part of a USB connector takes which line from the cable?

 

As ever, all thoughts and ideas gratefully appreciated

[timsabre]

Google is really your friend here. Google for "usb cable wiring" and click the images tab.

 

The odd thing is, USB is a 4 pin connector (Vbus, Gnd, D+, D-) and all the pins are needed to make it work. So I am not sure how it could work on a 3 pin connector? Maybe they have some custom hardware/firmware that works without detecting Vbus.

[jexjexjex]

The 5V power line is the one that is stumping me. I can only assume that it's not connected on the XLR as both the tablet and the data collector have their own power.

 

I'll report back as and when I know more...

[timsabre]

The 5V power line is the one that is stumping me. I can only assume that it's not connected on the XLR as both the tablet and the data collector have their own power.

 

 

Although it's used to power devices which don't have their own power, it is also used in the USB handshake process to detect when a host is connected and disconnected, at least on all the USB devices I've worked on.

[Brian]

Is it just a cable? Or could it be something a bit 'smarter'. When I read your post I thought 'FTDI' cable, ie something with a USB plug on one end with electronics moulded in which make it look like a USB serial port going to open ended wires at the other which has been soldered to an XLR.

 

[Modge]

Is it just a cable? Or could it be something a bit 'smarter'. When I read your post I thought 'FTDI' cable, ie something with a USB plug on one end with electronics moulded in which make it look like a USB serial port going to open ended wires at the other which has been soldered to an XLR.

 

My first thought also. Which do present you with a lot more three wires, but you're free to use them as necessary - if you don't need the 5V, you don't need to use it.

[dosxuk]

Well the first thing to note is that a USB-XLR for DMX is not a straight through cable. The cable is converting from the USB signal to the DMX signal as well as connectors. Unless, by shear coincidence, your data logger also uses DMX to communicate (very very unlikely), a USB-DMX won't be a suitable alternative.

 

As others have said, I would highly suspect there are electronics in the data logger cable which is converting from the USB signal to whatever proprietary protocol they have decided to use - and that will make it difficult to find a alternative.

[timsabre]

Of course... Didn't think of that

[jexjexjex]

Well the first thing to note is that a USB-XLR for DMX is not a straight through cable. The cable is converting from the USB signal to the DMX signal as well as connectors. Unless, by shear coincidence, your data logger also uses DMX to communicate (very very unlikely), a USB-DMX won't be a suitable alternative.

 

As others have said, I would highly suspect there are electronics in the data logger cable which is converting from the USB signal to whatever proprietary protocol they have decided to use - and that will make it difficult to find a alternative.

 

The more I'm looking at this, I think you're probably right. The USB does seem a bit bigger that a simple "connector". I'll just need to tell the boss that he's to stump up £120 for a couple of spares...

 

That'll make his Christmas!

 

Thanks for all the info.

[TomHoward]

Might be worth a shot in the dark with a USB-RS232 cable with the electronics at the usb end, connect the Rs232 tx, rx and ground? It's possible they've developed a proprietary protocol but seems unlikely if you could use one off the shelf.

 

Is the cable available as on older Comm port - USB style cable? If so this would make the above more likely

[Jivemaster]

You cannot get four wires from a USB out via a XLR3 so there must be something inside a connector, Actually there is lots of room in there for a chip,custom programmed.

[jexjexjex]

Might be worth a shot in the dark with a USB-RS232 cable with the electronics at the usb end, connect the Rs232 tx, rx and ground? It's possible they've developed a proprietary protocol but seems unlikely if you could use one off the shelf.

 

Is the cable available as on older Comm port - USB style cable? If so this would make the above more likely

 

No, the only other variation that I have on the cable is the older one that goes from standard COM port (9 pin?) to 3 pin XLR and it's just a straight wired through on 3 of the pins.

[Brian]

No, the only other variation that I have on the cable is the older one that goes from standard COM port (9 pin?) to 3 pin XLR and it's just a straight wired through on 3 of the pins.

In that case then, the USB version is almost certainly an active lead with a built-in USB to serial converter and TTL to RS232 driver moulded into the USB plug. FTDI have such a lead here for £17.25. It's highly likely, based on knowing the old version uses just three wires, that thy simply connect GND, TX and RX.

[TomHoward]

No, the only other variation that I have on the cable is the older one that goes from standard COM port (9 pin?) to 3 pin XLR and it's just a straight wired through on 3 of the pins.

Sorry, that's what I meant, Com-XLR not USB. In that case you could either use a generic USB-Comm port (available off EBay for £2 delivered) and cut a 9-pin cable in half, copy the pinout on the XLR and put the two pieces together, or if you want direct USB - XLR then you'd have to find one with the electronics in the USB end - which excludes the cheapest generic ones but you may find something.

 

The thing that made me think of this was the cheap USB programming cables for our Motorola radios - like EBay item no 251269333770 - which again are available as either a straight-through Comm cable or a usb cable like this - this may be one you can cut.

[DrV]

There are plenty of cheap usb-serial ports like this one http://r.ebay.com/bBHCQn which have the ftdi chip at the usb end

Dave