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fiber optic USB link

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teravolt

Thu Nov 27 2014, 09:15PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I am working on a version of the QCW and I am using a arbitrary waveform generator to produce the ramp. It uses a GUI driver that it came with and uses a USB link. I want to create a fiber optic USB link that is easy to build I am hoping. My idea is to isolate the computer from the wave generator so EMI won't be such an issue from the tesla. Is it pausible to use a glass fiber or plastic for D+ and D- ? is D- and D+ bi directional? I have been looking around the net but most units that will do this is ferly expensive.

Sulaiman

Fri Nov 28 2014, 03:10AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Wouldn't it be easier to connect the QCW control electronics directly to usb
(and possibly powered by usb?)
then have a F.O. link from the QCW control output to your QCW power electronics?

This way the QCW control is far frrom and isolated from the QCW high power / rfi stuff
and you will not have usb adapter problems.

Conundrum

Fri Nov 28 2014, 06:11AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Multiple optical wavelengths ie IR and blue might work.
I've found that UV laser diodes are very nice specific sensors and the same goes for the red diodes found in cheap laser pens.
Even if the diode no longer lases (ie COD) one taken out of a dead bluray optical block will normally work fine for this and it reacts to a 405nm blue LED nicely.

teravolt

Fri Nov 28 2014, 08:24AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

thanks for reply Sulaiman and Conundrum. what I did was make a class D amplifier with a analog input. The wave gen timing is integrated with the control circuitry so that the amp and DRSSTC turn off and on with the single wave coming out of the wave gen. the ramp width is controlled by the wave gen GUI

the pictures are of my layout for the controller and a USB isolator that works. when I first ran the power electronics and computer and control on my bench the computer did some weird things like losing link and the blue screen of death. Fortunately it was fixed by separating the computer ground from my controls ground using the isolator. However I am concerned if use a long USB, maybe 20 Ft., cable from the controls to my laptop it will act like a antenna. I want to create a fiber optic repeater for the USB . I have done some net research but there is a lot about protocol but how it works but not much on the hardware. I was hopping that D+ is something like computer to wave gen and D- is wave gen to computer. If the lines are bi directional than it will be harder. hopefully somebody knows or can point me in the right direction.

mister_rf

Fri Nov 28 2014, 09:31AM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

DIY optical isolation devices on the USB wires are difficult to obtain, because the signaling rate is 12 MHz, which is too high for cost-effective isolators. Also, you must carefully match the D+ and Dâ€“ signals for propagation delay and skewâ€”a difficult prospect when using optical isolators. In addition, the USB is bidirectional, whereas isolators are unidirectional, complicating the situation. Furthermore, in a peripheral with an integrated transceiver, the OE signal, which indicates direction, is inaccessible. More details here:

There are some commercial products designed for such applications. You need to search for USB Repeater. This will convert the USB signal into another signal, transmit it over some medium such Fiber Optic.
E.g.

BigBad

Fri Nov 28 2014, 10:29AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

You could go bit serial on the optical link and stick arduinos at each end to act as muxes maybe, there's less optical hardware that way.

Arduinos talk USB anyway.

Dago

Fri Nov 28 2014, 10:30AM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

There are premade optical USB 3/2 cables off the shelf, no additional electronics needed:

mister_rf

Fri Nov 28 2014, 10:47AM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

@Dago
The above example is not suitable for total electrical isolation as the fiber-optic isolation. Those cables are using copper wires also. See the manufacturer disclaimer:
â€œThis cable is designed to be compatible with self-powered devices using USB 3.0 and USB 2.0 interfaces. However, the USB-IF has not yet developed a specification for optical fiber transmission.â€

Ash Small

Fri Nov 28 2014, 11:17AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

There is a trick you can do with Android devices to get them to connect to any USB device, but you need to provide a separate power supply for the USB device, as Andriod devices can't power external USB devices. I assume you'll need to do the same here.

You can get 'repeater' cables for USB (I use them for USB 2) when connecting devices more than a few meters apart. These effectively 'buffer' the data stream, then send it on to the next 'repeater'. I imagine the best place to put the fibre optics may be between two of these 'repeater' units.

Maybe others will have different suggestions?

Steve Conner

Fri Nov 28 2014, 12:06PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

If it were me, I would use a Toslink cable from my laptop's optical audio output, to an audio DAC inside the coil. Then draw the ramp waveform in an audio editor like Audacity. Stereo, so one channel for the enable signal and the other for the ramp.

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