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

["Tesla list" <tesla@xxxxxxxxxx>]

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