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USB remote shutter - amount of current drawn when shooting?

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Offline ressa

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USB remote shutter - amount of current drawn when shooting?
« on: 25 / January / 2016, 19:16:05 »
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Hey friends,

I just installed CHDK on ,y IXUS160 and it works great! Thank all developers.

I have a question now:

I enabled "USB remote shutter" on CHDK and could remotely release the shutter using USB cable by just plugging it to computer (Half press) and unplugging it (full press). I am now planning to use this function in a multi-camera setup. I am thinking of using a USB hub. plugging 2 cameras into hub, then by just connecting and disconnecting the hub, both cameras could take picture simultaneously.

But here arises a question: USB is 5V, I want to connect two cameras, It seems that I should be worried about amount of current needed when shooting. maybe USB ports on hub would not provide enough power for remotely shooting. what would happen If I want to use 6 cameras and using two hubs connected to each other?

so I need to know how much current is being drawn from USB port while "half press" and "full press" are being done. then I can check if the 500mA from original USB on my laptop is enough for my setup or not.

Do you have any recommend for my setup? How could I get sure that I can have all my cameras remotely working?

Thanks

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Offline waterwingz

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Re: USB remote shutter - amount of current drawn when shooting?
« Reply #1 on: 25 / January / 2016, 20:14:09 »
Unless you have one of the very rare Powershots that will charge over the USB port,  you can assume the current draw on the USB +5V pin is essentially zero.  The camera senses the voltage there but does not draw any appreciable current  Think in terms of a few microamps.

As far as your mulitcamera rig goes, there are some basic concepts discussed here along with a bunch of useful links :  Multiple_Cameras_using_CHDK
« Last Edit: 25 / January / 2016, 20:16:50 by waterwingz »
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Offline ressa

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Re: USB remote shutter - amount of current drawn when shooting?
« Reply #2 on: 26 / January / 2016, 00:14:16 »
Thanks for your help, I read the forum and it seems that there is a capability called CDHK PTP which can be used for both "triggering cameras" and "downloading photos from camera to my laptop".

what about in that condition? should I consider amount of current drawn by camera while using CHDK PTP again in micro-ampere level?
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Offline waterwingz

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Re: USB remote shutter - amount of current drawn when shooting?
« Reply #3 on: 26 / January / 2016, 06:43:56 »
Quote from: ressa on 26 / January / 2016, 00:14:16
what about in that condition? should I consider amount of current drawn by camera while using CHDK PTP again in micro-ampere level?
Yes.
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline ressa

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Re: USB remote shutter - amount of current drawn when shooting?
« Reply #4 on: 26 / January / 2016, 06:54:22 »
Quote from: waterwingz on 26 / January / 2016, 06:43:56
Quote from: ressa on 26 / January / 2016, 00:14:16
what about in that condition? should I consider amount of current drawn by camera while using CHDK PTP again in micro-ampere level?
Yes.

Thanks, So I shouldn't be worried about amount of current drawn by multiple-cameras, for example If I make an arrangement including "10 cameras" parallel to a "single USB port" (using multiple hubs), I can manage them both whilst "triggering" and "data downloading". Did I get the point correctly?
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Offline waterwingz

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Re: USB remote shutter - amount of current drawn when shooting?
« Reply #5 on: 26 / January / 2016, 07:50:25 »
Yes.
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline ressa

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Re: USB remote shutter - amount of current drawn when shooting?
« Reply #6 on: 26 / January / 2016, 08:50:45 »
Another issue,
in the article "USB_Remote" it has been described an ability of CHDK called "Multi-Camera Synchronization".

it has been mentioned that cameras would wait for a "sync-signal" before actually taking the picture. now here is the question: How should I provide such "sync-signal" or "Shared-signal" using USB? how would cameras understand that this signal is the final signal that is sent simultaneously for all other cameras?

Here is the original text of wiki for "Multi-Camera Synchronization". I can't get the point of this explanation exacly:

A useful application of CHDK is the ability to connect two or more cameras together via a common USB cable so that their operations can be synchronized. The fact that the cameras are connected in parallel ensures that things happen at approximately the same time. To achieve better synchronization when taking an actual photograph, CHDK has the ability to stop the picture taking process immediately before the image is actually captured. This allows CHDK on several cameras to focus, adjust exposure, setup the flash and then wait for a shared signal to complete the shot (i.e. sync). If the Enable Sync option is set in CHDK then each camera will wait for the final transition of the USB signal ( 5V to 0V ) before shooting.  Note : the camera will wait a maximum of 10 seconds for the sync signal.  Waiting any longer results in unpredictable bad camera behaviour.
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Offline waterwingz

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Re: USB remote shutter - amount of current drawn when shooting?
« Reply #7 on: 26 / January / 2016, 10:25:58 »
Quote from: ressa on 26 / January / 2016, 08:50:45
How should I provide such "sync-signal" or "Shared-signal" using USB? how would cameras understand that this signal is the final signal that is sent simultaneously for all other cameras?
There are basically two ways to "sync" multiple cameras so that they all shoot at once.   They were originally developed for use with two camera systems used to create stereographic (i.e. 3D) images.

The first method is a hardware solution that sync's shooting using the +5V pin of the camera's USB connector. CHDK can be configured to start shooting when the +5V pin on the camera's USB connector has 5V applied to it.  It will focus and set exposure and then wait for the voltage on the +5V line to be removed.   If 2 (or more) cameras have their 5V line connected in parrallel then they will all start shooting when the +5V line has voltage applied and they will complete the shot when the voltage is removed.

The second method is a software solution using USB communications. With this method, all cameras are connected to a computer using USB cables and hubs.  The PC sends messages over the USB connection to command camera operations.  The connection is fast enough to allow the PC to tell each camera to shoot and they will all appear to shoot simultaneously.  The precision of the syncronization can be tweaked a bit by calibrating the various delays in the system.

The second method can be implemented using standard USB hubs and a PC.  The first method requires custom hardware but can be implemented without needing a PC.  Both solutions can provide adequate sync for multi-camera setup but the first (hardware) method will generally provide more precise sync than the software method.

Which setup you use is a question of which are good enough and the most cost & time effective for you needs.
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Ported :   A1200    SD940   G10    Powershot N    G16
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