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Old Aug 2, 2005, 11:39 AM   #1
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hi, I use Vivitar 3200a flash with my oly c770 but the problem is its trigger voltage is high near 55v so i think its unsafe to use. or i can use it? can i use voltage regulator ic like lm7805 to lover its voltage to 5v is it possible . now i want to use another vivitar 2800 flash also using a hotshoe adaptor. its trigger voltage is 35v. can i use both of them
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Old Aug 2, 2005, 12:09 PM   #2
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tilgates wrote:
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hi, I use Vivitar 3200a flash with my oly c770 but the problem is its trigger voltage is high near 55v so i think its unsafe to use. or i can use it?
IMO, only Olympus can state it's safe or not
In doubt, you can use this:
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can i use voltage regulator ic like lm7805 to lover its voltage to 5v is it possible .
In theory no. The 55v trigger voltage has to be pulled down to 0 v (shorted) to trigger the flash circuit. The 7805 act like a ballast resistor and will leave around 50 v at the flash terminals. Well, it may works because of the in rush current (I never tried) , but it's not a technically "clean" way.
If you are familiar with electronics, try an optoisolator SCR or triac (the part cost even less than a 7805 :G).

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Old Aug 2, 2005, 12:10 PM   #3
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KCan wrote:
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In doubt, you can use this:
http://www.weinproducts.com/safesyncs.htm


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Old Aug 2, 2005, 12:18 PM   #4
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thanx

Im thinking to use optoisolator ,but willsingle icwork with both the flashes,

can u plz give me the simplest drawing of this circuit , im newbee to electronics.
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Old Aug 2, 2005, 3:34 PM   #5
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tilgates wrote:
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thanx

Im thinking to use optoisolator ,but willsingle icwork with both the flashes,

can u plz give me the simplest drawing of this circuit , im newbee to electronics.
I forgot that question, ... in fact, you better not connect the 2 flash together directely, but with 2 separate isolators to be ... electrically clean :lol:, get back to you later .

BTW, what I said above is not true; the 55v , if thereis enough powerat the source, will not even change , the ballast (the 7805) will take the 50 v remaining voltage( But in the reality, the source is not that powerfull )
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Old Aug 2, 2005, 6:08 PM   #6
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Hi again, some related thread:

http://www.stevesforums.com/forums/v...mp;forum_id=78

http://www.stevesforums.com/forums/v...mp;forum_id=53

http://www.stevesforums.com/forums/v...mp;forum_id=53

You can use this :



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Old Aug 2, 2005, 9:43 PM   #7
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thanx for the diagram.

ok i m going to tryout the optoisolator. but why are the safesyncs available in the market are so costly do they use some other type of circuits.
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Old Aug 2, 2005, 10:03 PM   #8
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tilgates wrote:
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thanx for the diagram.
UR welcome

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but why are the safesyncs available in the market are so costly do they use some other type of circuits.
I don't know , and not really interrested to the point to buy one and take it appart :G
IMO, they are expensive because the market is not that big (in quantity I mean). They have to amortize the cost and also make money of course. Although the electronic parts are cheap, there are also accessories like jacks, connectors, casing, and labor.


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Old Aug 3, 2005, 4:00 AM   #9
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Hi K

I made a simplified version of your circuit. On the lash up on a breadboard using a normal "push on" switch in place of the camera switch. It worked great, so i made it up. Using a digicam it worked for the first flash but the triac stayed on, so the flash would not charge up. The silly thing is it works OK with a CANON 10d but not a 350d. I am showing a sketch of the circuit.
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Old Aug 3, 2005, 10:01 AM   #10
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geriatric wrote:
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Using a digicam it worked for the first flash but the triac stayed on, so the flash would not charge up. The silly thing is it works OK with a CANON 10d but not a 350d. I am showing a sketch of the circuit.
I think the reason is that the led with the 100 resistor sustain a current (around 15 mA) in the camera hotshoe circuit , which is probably an SRC or a Triac itself, and that current prevents the camera's SRC or triac to switch to off state.
May be the 350d use a bigger SRC, so that the curent is not enough to maintain it's on state .


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