Need help selecting relay (or an alternative)

[ravix]

Hey guys, I am pretty new to this, but I am taking electrical circuits this year so you'll probably get to know me pretty well.

I am trying to build a trigger cable to sync my digital camera and some flash slaves I own. I've used a multimeter to take some readings, and I think I need a relay to get this to function, but the behavior is a little strange and I don't know what to get.

Don't worry, I have a diagram


**broken link removed**

Basically, I have four wires, which I'll call C, D, A, and B. The voltage difference between C and D is normally 3v, with a current of .3amps running through the wires. When the flash slave triggers, the voltage drops to .55v and the current stays the same. At this moment, I need to rapidly short out wires A and B.

It seems like I need a normally closed relay that opens up at around 2.5v, and closes again at around 1.5v to be safe. Does this sound right? If so, where can I find something like this in the United States?

Also, what kind of response time can I expect from such a relay. ie: Milliseconds, Microseconds, 2 seconds (hopefully not ).

Thanks guys, I appreciate the help.

btw: The slaves are pocket wizards and the camera is a 20d if any of you have any better ideas.

-Eric

 

[Rolf]

Hey guys, I am pretty new to this, but I am taking electrical circuits this year so you'll probably get to know me pretty well.

I am trying to build a trigger cable to sync my digital camera and some flash slaves I own. I've used a multimeter to take some readings, and I think I need a relay to get this to function, but the behavior is a little strange and I don't know what to get.

Don't worry, I have a diagram


**broken link removed**

Basically, I have four wires, which I'll call C, D, A, and B. The voltage difference between C and D is normally 3v, with a current of .3amps running through the wires. When the flash slave triggers, the voltage drops to .55v and the current stays the same. At this moment, I need to rapidly short out wires A and B.

It seems like I need a normally closed relay that opens up at around 2.5v, and closes again at around 1.5v to be safe. Does this sound right? If so, where can I find something like this in the United States?

Also, what kind of response time can I expect from such a relay. ie: Milliseconds, Microseconds, 2 seconds (hopefully not ).

Thanks guys, I appreciate the help.

btw: The slaves are pocket wizards and the camera is a 20d if any of you have any better ideas.

-Eric

Have you thought about using the camera flash for sync?
Here is how I do it.
https://www.pbase.com/sinoline/pic_slave_flash

 

[ravix]

For my needs an optical slave system will not do. Pocket wizards are radio units than can sync up to 1600ft away and they won't fire when someone nearby with a camera fires their flash.

But thank you for the link.

 

[eblc1388]

A mechanical relay would be slow to react. Expect to get 30-300ms delay when signal drops and relay operation.

If solution other than using a relay is desirable, then your question is missing the following vital information.

What voltage are between A & B? AC or DC? Do you need electrical isolation between signal and A,B?

How much current will pass from A to B if a short circuit is applied?

 

[Rolf]

For my needs an optical slave system will not do. Pocket wizards are radio units than can sync up to 1600ft away and they won't fire when someone nearby with a camera fires their flash.

But thank you for the link.

Check this link:
https://www.lukemiller.org/journal/2005/05/making-extendable-remote-release-for.html
There are no indications of a relay as far as I can see. These Canon remotes looks very similar to my old Minolta D7. Just a common, a focus and a shutter release. Two switches should do it.

 

[ravix]

Thanks for the responses guys, I really appreciate them!

Rolf: that link is a great resource, unfortunately I have already covered that ground. I bought one of those triggers off of ebay as a source for my plug, which takes the roll of A and B in my diagram. HOWEVER, instead of triggering with a physical switch, I need it to trigger when my pocket wizards give the signal, which is previously described.

eblc1388: Thanks for the help, I'll do my best to get the information you asked for. It appears there are three volts across A and B. As soon as they are shorted the camera fires. Similarly, when the camera fires, the voltage drops to zero. This behavior is remarkably similar to the behavior of my pocket wizards, however if I connect them directly to one another the camera repeatedly fires. Electrical isolation is not necessary with this setup.

Edit: I figured it out. I had two wires crossed that caused it to not work properly. As usual, a simple fix to a complicated problem.

Thanks again everyone!