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A fiber optic trigger lead for (DR)SSTC`s



Original poster: Finn Hammer <f-h@xxxx>

All,

I had some problems with back-emf into the Roland synthesiser, driving my musical TC`s, so I wanted to look into using fiber optics as the media for supplying the trigger impulses.

I wanted to use cheap polymer fiber, and the transmitters and receivers off the Industrial Fiber Optics, Inc.`s line, and I have some promising results already.

As the pulse driver, I built Stephen Wards pulser, without the burst mode add on:
http://www.stevehv.4hv.org/interrupter/intwbmsch.JPG


I chose the IF-E96 660nM red Led as the transmitter, because it is bright and able to 5Mbps. This one is driven btwn. output of the pulser and ground with a 680ohm series resistor.

As the receiver I chose the IF-D96, which is an inverted schottky photo transistor, also capable of 5Mpbs. The output of this device is normally high, and goes low when it receives enough light.

For the scope shots supplied, I used 50meters (150feet) of HFBR-RUS 100 polymer optic cable btwn transmitter and receiver.

This pic shows the mockup, and the roll fiber cable:
http://home5.inet.tele.dk/f-hammer/mockup.jpg
This first screensnap shows good correlation btwn. transmitted signal ch.1 and received signal, ch.2 at 283 BPS
http://home5.inet.tele.dk/f-hammer/3pulses.jpg

Next one shows same, at a 164µS pulse:
http://home5.inet.tele.dk/f-hammer/1pulse.jpg

Zooming in on the front edge reveals a 400nS turn on delay
http://home5.inet.tele.dk/f-hammer/frontedge.jpg
(the front edge of the transmitter might be improved on with proper layout technique)

The trailing edge shows about the same 400nS delay:
http://home5.inet.tele.dk/f-hammer/rearedge.jpg

So the signals pass trough. In the transmitter end, conversion to fiber optic is as simple as adding a resistor and the led. In the receiving end it is a matter of tailoring the output to the trigger circuit. A comparator, a schmidt trigger, perhaps inverting, will do the trick.

The digikey part nos are:
Transmitter: FB128-ND
Receiver: FB132-ND

A warm thanks to Terry Fritz for generously donating the parts for this project.

I always thought it reckless to hold a trigger generator in my hands, grounded braid or not. With these fine optic parts, it does not have to be like that any more.

Cheers, Finn Hammer