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