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Old Dec 28, 2005, 5:05 PM   #1
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I am trying to make a circuit that will fire a slave flash on the second flash from my Olympus C-740UZ.

I got the idea from here.

The idea is to use an optical slave trigger to toggle a d-type flip-flop in toggle mode. The flash is connected to a optoisolator. The output of /Q and from the slave trigger is AND'ed together, hopefully setting off the flash.

/Q is initially set. The first flash will toggle the FF and /Q will be reset. The second flash will toggle the FF again and /Q will be set. With the clock pulse AND with /Q, it should turn on the LED in the optoisolator and fire the flash.

I have it built on a breadboard but when I use my camera's flash to trigger the slave with this circuit, nothing happens :sad:. The optical slave trigger works with the flash.

I am not sure of the problem. It seems the FF is not being clocked. I assume the voltage level coming out of the slave trigger is too low to be a valid logic 1 or the pulse is too narrow.

I would appreciate some help in trying to get this circuit working. Hope this circuit will help other forum members once it is working.

I have attached the circuit that I current have put together.

Thanks,
Morgan
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Old Dec 28, 2005, 7:31 PM   #2
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I took a look at kcan's MFI2 circuit at how kcan clocked the counter. I applied that bit of kcan's circuit to mine and got the optical slave trigger to trigger the flash with the circuit but the flash only fires with the first flash from the camera.

Here is the revised circuit.
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Old Dec 29, 2005, 8:47 AM   #3
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Can you put a scope on the input of the optical trigger?
1. There may be extra noise glitch on the clock input that C3/R5 can't filter out
2. Are you assuming a negative going pulse?
3. When do you hit PB1 (i.e. after the optical is attached or before) ?

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Old Dec 29, 2005, 3:48 PM   #4
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NHL,

No, I don't have a scope to look at the input.
1.) I don't know if there is extra noise or not there.
2.) I am assuming a postive going pulse.
3.) The PB is used to reset the FF so /Q will be set again.

So far, the /Q goes to reset and stays there.

I am thinking that a FF is not the way to go to remove the camera's preflash.
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Old Dec 29, 2005, 4:50 PM   #5
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mcwc wrote:
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I am thinking that a FF is not the way to go to remove the camera's preflash.
I think so too - I never like asynchronous circuit myself...
-> The pulse is usually active low (short to ground) since the Vcc is used to power the drain/collector. It's also a good idea to limit the curent here...

Why don't you just use KCan circuit?
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Old Dec 29, 2005, 5:51 PM   #6
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I was trying to keep things simple and use ICs I have laying around from school, that's why I didn't use kcan's circuit.

From here, how good is it to use a monostable?
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Old Dec 30, 2005, 11:33 AM   #7
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The monostable is a more robust design since it introduces a delay which you did not have before (also notice the low going input pulses) - Your previous circuit can easily introduce a glitch when both input are valid simultaneously on the output.

IMO a more robust design will be using a PLD (still a single chip), such as 22V10 and use a state machine to sequence through the two pulses:
1. It's a synchronous design (the input signal is sampled instead)
2. You can double samples the signals before switching states

... Many ways to skin a cat!
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Old Dec 31, 2005, 1:13 AM   #8
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Well, finally got a working circuit. Used a few schmitt triggers to shape the pulse from the slave trigger to clock a 2-bit synchronous JK up counter.

Now to figure out to auto reset after count "10".
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Old Jan 22, 2006, 12:37 PM   #9
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Good idea.

Here is my SFT project.

http://www.fancon.cz/slave-flash-tri...-flash-en.html


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Old Jan 25, 2006, 10:00 PM   #10
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Thanks sharing your solution jankop!

Anyways, I have gotten my circuit to automatically reset after each flash. The circuit is ready to use after turning on the power, so there is no need for a reset button. Just a LED to show if the circuit is on or not.

For those who will use this circuit, have fun!
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