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can I use the Arduino to simply create a close contact over three wires.
Not without extra hardware such as a relay or MOSFET
Do you want the three wires to act as a changeover circuit or something else ?
Details or better still a schematic please
just need a transistor !!!!
Hi,
Welcome to the forum.
Please read the post at the start of any forum , entitled "How to use this Forum".
OR
http://forum.arduino.cc/index.php/topic,148850.0.html.
We will need to know what the three contacts do and how they are connected to make the camera respond.
As a guess I would think one terminal is a signal common which you connect to the other two contacts to activate auto-focus and take the picture.
Tom... 
Just Google for the make/model of camera.
Mikecl1266:
My question is can I use the Arduino to simply create a close contact over three wires.
There is no voltage needed as a trigger.
Three wires? Arduino GND to camera GND is first. Arduino pin to camera trigger is second.
Where is third?
No V needed sounds like the camera has a pulled-up pin that you ground to trigger.
The Arduino can source or sink 20mA safely.
It can also make the pin neutral as an unread INPUT.
And by using port manipulation it can change pin state in about 1/4 microsecond -- handy when reading a button matrix quickly.
If the Arduino is 5V and the camera is 3.3V it only takes a diode stopping the 5V to make wire two safe.
While the Arduino pin is OUTPUT HIGH the diode blocks the 5V, the camera sees its own pullup 3.3V.
Arduino pin LOW lets camera pullup current drain and the camera pin sees LOW and triggers.
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How many wires? 3 might be 2 channels (RX/TX) plus ground serial, not a simple switch. 3 might be 2 switches plus ground.
Have you touched any of the bare wire ends together? You began with no voltage needed?
I assume from the first post that you do know some things about the camera and cable.
GoForSmoke:
No V needed sounds like the camera has a pulled-up pin that you ground to trigger.
I don't think that is a safe assumption. It's much more likely that the OP has no idea how the trigger system works.
And even if your guess is correct it would be unsafe to connect an unknown voltage to an Arduino pin.
...R
Robin2:
I don't think that is a safe assumption. It's much more likely that the OP has no idea how the trigger system works.And even if your guess is correct it would be unsafe to connect an unknown voltage to an Arduino pin.
...R
The Arduino pin is to switch those wires OPEN/CLOSED. The pin can trigger a transistor or opto-isolator to do that.
GoForSmoke:
The Arduino pin is to switch those wires OPEN/CLOSED. The pin can trigger a transistor or opto-isolator to do that.
Agreed. But you did not mention them in Reply #5 and I had visions of the OP connecting something unknown to his Arduino with unpleasant consequences.
...R
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Relay is slow and takes power to switch while the FET is near instant and takes a signal to switch.
An opto-isolator is a photo-transistor coupled with a led. Using one of them lets the Camera and Arduino not even share ground. That is a point of isolation. A single channel opto has 4 pins and can be spliced into a cable with connectors and good use of heat-shrink tube. Opto is fast but opto downside is it takes at least a couple mA to hold open.