Hey all. I just recently ebay'd up a Vivitar 285 flash to work with my
Pentax *ist-DS DSLR. I measured the trigger voltage at 8V, so it's more than happy
working with it. I contacted Pentax awhile back and they told me the deviced used in
the trigger circuit is rated at 480V, 1.26A

Anyway, I'm looking to add a few things onto this unit. I'd like to get the
remote sensor cord, but I'm also thinking of trying to build some other circuitry to
run a few things. In particular, I'd like to find out if the flash is designed to
allow external quenching through the sensor plug. I've looked at the guts of the
sensor, and it appears to be wired as follows:
1-2 connected internally
3 n/c
4 R+
5 R-
6 n/c
The pin numbers are counterclockwise, looking at the *flash* (not sensor),
starting at the first one from the key (i.e. pin1 is approx 2 o-clock, pin2 is 12
o-clock, etc). #6 is the center. The resistance between R+ and R- is 24k for 1/16,
92k for 1/4, 168k for 1/2, and of course open-circuit for full M. The colored modes
look like they've got a resistor in series with the CdS cell, but I didn't bother to
measure those. Also, I noted that with the sensor removed, there is no voltage at the
hotshoe and it won't trigger... probably the pin1-2 jumper in the sensor.

Does anyone have any more detailed info than this? I'm looking for a
schematic, post-mortem, or a cable pinout. My ultimate goal would be to build a TTL
circuit for these units to dedicate them to bodies, or at the very least allow one
flash to act as automatic master for other slaves.

Thanks,
-Cory

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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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