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Old camera speedlight low voltage trigger conversion
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StillTrying:

--- Quote from: cprobertson1 on June 19, 2019, 09:58:17 am ---Side note: do relays switch fast enough? The part you linked to lists 0.5ms including bounce - so if the shutterspeed is as faster than 1/2000 I may actually miss the flash (plus any other delays in the trigger circuitry on the flash itself)!
--- End quote ---

When you enable flash your camera will ignore the 1/2000 and fix it at 1/100 or 1/200, because the shutter has to be fully open for all of the 30us to 2ms of the light flash, I don't think an extra 0.5ms delay to the 5ms or 10ms shutter time would make any difference.

Just wire a thyristor to the flash and apply 4 or 5V to it's gate, you'll find there's nothing to it! But be very careful the 380V doesn't go through you or the scope.
On my cheap flash it's possible to make contact with the outside ring of the ext trigger, and the center pin of the hot shoe at the same time, which occasionally gives me a surprise.

The problem with isolation is some power is needed on the camera side.


--- Quote from: floobydust on June 18, 2019, 10:52:12 pm ---One question is the configuration of a low voltage camera hotshoe. It seems to be open-collector with a weak pull-up resistor to camera's Vcc?
--- End quote ---

The middle of this page suggests there's a weak 6V coming out of the camera which can be stored and used to trigger the opto's input side, I've never heard of it myself.
https://electronics.stackexchange.com/questions/242088/connecting-a-camera-hot-shoe-to-a-homemade-strobe
cprobertson1:

--- Quote ---When you enable flash your camera will ignore the 1/2000 and fix it at 1/100 or 1/200, because the shutter has to be fully open for all of the 30us to 2ms of the light flash, I don't think an extra 0.5ms delay to the 5ms or 10ms shutter time would make any difference.
--- End quote ---

Ah, nice! That makes sense! I'm forgetting the camera will override settings - I've not actually used a flashgun with a modern camera before - the last one I used was an entirely manual film camera, and even then I was pretty young!



--- Quote ---The middle of this page suggests there's a weak 6V coming out of the camera which can be stored and used to trigger the opto's input side, I've never heard of it myself.
--- End quote ---

Now that's interesting! I'll probe around with that as well - though Im currently leaning towards just using two CR2032s in series for the camera-side power.

With the CR2032 x2, running for <1s at 10mA coil current, I'm reckoning I'll be able to get 10'000 discharges from it.


--- Code: ---~235mAh*0.66 (to account for poor battery conditions) =155mAh
155mAh/10mA=15.5 hours=55800 seconds >> 10'000
--- End code ---

So, let's assume for argument's sake that the coil runs for a whole second each time the flash is fired, those cells should be more than happy for a good 10'000 shots.

Let's just run that again with Watt-hours just as a quick sanity check:

--- Code: ---~235mAh = ~650mWh (according to the datasheet's energy density figure - I'm actually getting 470-to-705mWh when I perform the calc. myself, depending whether I use the final voltage or the nominal voltage.)
650mWh*0.66=430mWh
Relay @ 10mA, 5V = 50mW
430mWh/50 = 8.58hours = 30888 seconds >> 10'000
--- End code ---

Okay, I'm not too happy I got a different figure there... I must have done something dumb. Still over 10'000 shots should be possible even if that calculation hasn't raised my confidence any! ::)

I'm now scratching my chin trying to figure out why those numbers aren't particularly close to each other... it may just be that mAh are a bad way to measure battery capacity, but I was hoping the figures would have been a bit closer than that...


StillTrying:
Have you blown anything up yet. :)

235mA/10mA = 23 hours = approx. 82,000 1sec triggers.

The flash's 380V only has to be shorted for about 4us so you could reduce the camera's trigger to just a 30us pulse through an opto or ~3ms for a small relay and even smaller batteries would last forever.
You can usually see the trigger transformer ringing by bringing the flash near to a scope probe, no physical connection is needed, it only rings for a few us, then there's another 5-8us delay before the tube lights, I've watched it many times!
Peabody:
I believe your Pentax uses a standard hotshoe, but my memory is the Hanimex is for a Minolta hotshoe.  If that's true, the Hanimex will not fit on your Pentax.  I mean it physically will not fit.  You didn't say what model your Sunpak is.

I would just encourage you again to use these old flashes off-camera.  You will find that the results you get with off-camera lighting make it look like you know what you're doing, even if you don't, and of course your camera would not be at risk from high voltage.  You would need a light stand, an umbrella adapter and an umbrella, plus some way to deal with the high voltage.  And you can get a basic wireless trigger set for $20.  This would be manual triggering of course - both camera and flash(es) in manual mode.  None of this ETTL rubbish.  :-)

floobydust:
A relay adds a huge delay 3-10msec to operate, are we really thinking a flash that late is going to work?

I took apart an old bounce flash I have, it's got a 800uF capacitor (!) and about 160VDC at the shoe and 320VDC for B+. Like an old Metz I repaired, serious sized capacitor.
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