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 Question for school project. Trying to find more info 
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Joined: Sat Sep 28, 2013 5:17 pm
Posts: 2
Post Question for school project. Trying to find more info
Hi all!

I'm trying to find out some more info for a school project I'm trying to do. My project is basically building a simple bramper using a micro controller my professor has provided. I'm been trying to scour the net for more info and it's been REALLY interesting seeing how other people build cool projects to interface with their cameras!!

Anyways, I've been trying to find specifications on the camera serial port and the flash port/pc sync for the camera. But it seems to come from a lot of tribal knowledge. Or more likely, what I'm trying to find is buried under a lot of unrelated search results.

Am I correct to assume the following: the serial port is there to tell the camera the take the picture?? So give it about 6-7volts to tell it to take a picture. Put it back to 0 to tell it to stop taking picture, i.e., releasing the shutter button? So if connect a circuit, it acts like a intervelometer?

However, what I'm getting confused (like an itch on the back of brain..) is why do devices such as the little bramper (http://www.thewhippersnapper.com/LittleBramper) need to connect to the flash port?? I've been trying to figure that out...

My guess is that it uses the flash port as a way to keep track of how long you tell the camera to take the picture, like a feedback loop. So you send the camera via serial port...listen on the flash port/pc sync port..if it registers a "high" (or whatever it does to tell you shutter is open), count down until it hits the time you want and then you send the camera to close the shutter via serial port.

Am I correct in my guess?? Would appreciate any help! it's been nagging at me...

Also, if one were to incorporate usage of the flash, I assume you send a signal continuously and detect it when it goes high since the camera acts like an open switch until the shutter is open, at which time, it'll close??

Sorry for all these ignorant questions. But I've been trying to find out info before troubling others. Might google-fu might be lacking since I spent the whole afternoon trying to find more info by myself :/

Thank you in advance!

Rex

edit: i was mixing up my terminologies. Fixed paragraph to make sense.


Sat Sep 28, 2013 5:43 pm
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Joined: Tue Apr 05, 2011 6:16 am
Posts: 487
Post Re: Question for school project. Trying to find more info
I'm not sure if you mean the USB port or the remote shutter port by "Serial port" (the USB port is the only 'serial' port on most cameras), but I'm presuming you actually mean the remote shutter port.

The remote shutter port and the PC Sync port both act as closures - one is used to signal the camera (the remote shutter port), and one is used to signal external devices by the camera (the PC sync port).

You don't "send 6-7 volts..." to any port on the camera. The remote shutter port expects to be treated like a switch closure. There is one common line, and then 2-3 signal lines depending on the model of the camera, typically there are two: shutter and focus. Connect either signal line (or both) to the common line from the port, and it activates that function. Don't think about "sending voltage" with the remote shutter port, think instead of connecting lines via a switch. You should isolate any connection between your device and the camera's remote shutter port to guard against differences in potential and screw-ups you may make in your early circuit design - opto-couplers are de rigueur here.

The PC Sync port is used by the camera to signal an external device when the shutter actually opens and closes. There are two contacts, and the camera connects them together as a switch closure. They are connected when the shutter opens, and disconnected when the shutter closes. Consider trailing shutter flash activation, this is how the old flashes did it.

You would monitor the signal on the PC sync port (for example, pull the main signal HIGH and when it reads LOW, the shutter has opened) to determine the actual amount of time the shutter is open, as there is lag between a remote shutter trigger and the actual trigger. In addition, when triggering via the remote shutter port, the actual amount of time the shutter is held open when operated in bulb mode varies, due to debouncing and other operations of the camera regarding the monitoring of the remote shutter port. The PC sync port timing can be used to account for drift in expected exposure time.

To use the USB port, you would need to speak PTP which is more complex than using the remote shutter port, but can be much more featureful. Some cameras, like Pentax, make it even more difficult by tunneling PTP over a SCSI protocol.


Tue Oct 01, 2013 6:33 am
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Joined: Sat Sep 28, 2013 5:17 pm
Posts: 2
Post Re: Question for school project. Trying to find more info
Thanks for the reply that helped a lot!


Tue Oct 01, 2013 10:05 pm
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