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How to Use this for fiber interrupter setup

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Danielle

Fri Jun 01 2007, 09:42AM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

I got this board from a DD audio setup and it uses lasers to sent the 5.1 Chanel data. there are 2 receivers and 1 transmitter on the board. the set up is well laid out should I desolder all of them and re mount the diodes? how should I set up the transmitter and reseavers. (they run at 3.3V ) It should be very good for an interrupter when its done.

thedatastream

Fri Jun 01 2007, 10:53AM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

I've done something similar on my DRSSTC with an SPDIF cable and I have found that:

1) the SPDIF receiver (I used) gives a pulse on the rising edge of a waveform and one on the falling edge. You could stick this into a toggle flip flop but there's the chance that if it misses a pulse, it could get stuck on for longer than you want and cause severs damage to your coil.

2) Removed the receiver from its housing and drilled it out for a 5mm photodiode (SHF213) with a zero bias op amp circuit (see below). Problem now was that the transmitter was not powerful enough, even when run from 9V (it was 5V rated). The spare op-amp is run as a comparator - it's a bit slow but does the job.

3) I then removed the emitter, drilled out the housing and replaced it with a super bright 20Âº beam width red LED. this is driven at 25mA from the output of a 555 timer.

A lot of faff but it does the job.

Of course this was my experience so Your Mileage May Vary

James

Paul Benham

Fri Jun 01 2007, 12:21PM

Registered Member #570 Joined: Wed Mar 07 2007, 03:41PM
Location: Winchester Uk
Posts: 42

The ones I used had a 5V supply, ground, a resistor on the transmitter to set the LED current, and an input for the TTL data. The receiver had supply, two grounds and an output. They were TORX176 and TOTX176. Have a look on the PCB for the connections and note any components nearby that may be setting Tx current or something similar. You may be able to get a data sheet for the devices, then you will know for sure how to use them. Not all of them work from DC upwards. Cheers, Paul.

Steve Conner

Fri Jun 01 2007, 12:58PM

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

The problem with a lot of TOSLINK parts is that the receiver is AC coupled, which makes it blind to low-frequency signals. Another forum member, jrz126, solved this with a clever trick where he modulates the transmitter with a 4MHz clock. I've heard rumours that some have a frequency range down to DC, but haven't seen it with my own eyes yet!

Paul and James, where did you get your transmitters and receivers? I'm looking for some but I don't have a credit card that Farnell would take :(

...

Fri Jun 01 2007, 03:17PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Something I should point out is that (contrary to the first post) toslink parts do not use lasers, but rather LEDs. It doesn't really matter, but for refrence.

In any case, I like the idea of having a simple oscillator running at some high frequiency (few mhz) that is interupted by the interupter, and then send the 4mhz pulses into the transmitter. At the reciever you put a small r/c filter (with a time constant of about .5uS) and feed the resulting stream of demodulated data into the gate driver chips.

Jrz126

Fri Jun 01 2007, 04:53PM

Registered Member #242 Joined: Thu Feb 23 2006, 11:37PM
Location: Erie PA
Posts: 210

I used a 4 pin crystal thingy from an old motherboard that I had lying around. It was much easier to use than the 2 pin oscillator which needs some other circuitry in order to oscillate.

Here are the schematics:
Reciever
Transmitter

Danielle

Fri Jun 01 2007, 09:08PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

Thanks for the help but one thing to note is they are laser diodes not LEDs and I have removed them but kept the casing so I can use the same type of plug. I am working on the oscillator and will post how it goes.
Also I forgot to mention on the board it goes through a syncroness flip flop before going to the diodes. I do wounder if these are my best choose now I also have a computer gigabyte fiber card where the diodes still work would that be better? how would I build a surcuit around that. Should I monitor the power and replicate the voltage so I don't over do it?

Thanks for the help.

...

Fri Jun 01 2007, 10:52PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I am quite sure they are LEDs, just because it is in a to-can doesn't mean it is a laser. All of the transmitters I have looked at have had a wide spectrum from ~600-670nm. This is a large part of the reason why you aren't supposed to use toslink cables longer than a few meters.

The network card on the other hand probably has a laser diode, and it probably doesn't have any extra circuitry in the tx/rx so you would be able to send the low frequency signal strait into the laser. But keep in mind that the fiber for telecom is much more delicate than for audio. It is probably also more expensive, and you have to make sure that you get the right diameter/wavelength. To use the telecom diode you would have to make a constant current driver (I don't know how much current you need off the top of my head, probably a few ma) although you should be able to get away with just using a resistor in series with the output of the 555. I worry more about the receiver end, as you will only have a few hundred uA to work with, and that is where all of the noise is.

Danielle

Fri Jun 01 2007, 11:38PM

Registered Member #632 Joined: Mon Apr 09 2007, 01:09AM
Location:
Posts: 267

Thanks for the advice Ill dismount the network card tonight being very careful. I already have a 100ft and 200ft cable for the card so this shouldn't be a problem with the cable. Ill do some research to figure out how to best operate the diodes. I just got a nice fast electric motor so I may build my first SGTC with it as the rotary SG. I have 2 MOTs so I could use them in sires under oil. They are from 2500W old commercial MOTs so this should be good. Do you think I could use my bank of bottle caps for the main capacitor they are 12 sanpelligrino bottles.

...

Sat Jun 02 2007, 02:43AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I don't have a slightest clue what a sanpelligrino bottle is, but chances are that for a mot coil you will need an insane number of bottle caps.

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