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Another USB shutter question...

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Offline CMC68

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Another USB shutter question...
« on: 26 / August / 2009, 07:15:07 »
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Apologies if this is an aged old question, but I have searched and can't find the answer - probably because I am not using the correct terms.

Can CHDK as is, or a script available, allow a single pulse/signal (4.3v for 1/1000th sec) to both half press and fire the shutter over USB?

Thanks.

Chris
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Offline Microfunguy

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Re: Another USB shutter question...
« Reply #1 on: 26 / August / 2009, 11:47:29 »
Quote from: CMC68 on 26 / August / 2009, 07:15:07
Can CHDK as is, or a script available, allow a single pulse/signal (4.3v for 1/1000th sec) to both half press and fire the shutter over USB?

No, it is far too short.

The USB memory-mapped I/O is only checked every 10 msec and a pulse would need to exist for at least 20 msec to be detected most of the time.

Occasionally, even that may not be detected if the Camera firmware interrupts the keyboard code.

Can you describe the equipment you are using and what you are trying to achieve ?


David
« Last Edit: 26 / August / 2009, 11:49:38 by Microfunguy »
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Offline CMC68

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Re: Another USB shutter question...
« Reply #2 on: 26 / August / 2009, 14:37:22 »
Hi David, and thanks for replying.

I'm trying to fire my shutter with a device I currently use to trigger a flash for high speed photography.

My original thread, with contributions from the manufacture/designer of the flash trigger is here http://chdk.setepontos.com/index.php/topic,4078.0.html where he has told me that one of the devices outputs gives the 4.3v for 1/1000th of a second.

Any thoughts/suggestions appreciated.

Chris
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Offline Microfunguy

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Re: Another USB shutter question...
« Reply #3 on: 26 / August / 2009, 15:49:32 »
Quote from: CMC68 on 26 / August / 2009, 14:37:22
the devices outputs gives the 4.3v for 1/1000th of a second.

The circuit that anaglyphic gave can be used to briefly pull the +5V low.

As usual, I can only advise how it could be done with SDM, others will have to say if it is possible with CHDK.

In SDM's normal synch mode, close a switch to put a permanent 5V on the USB.
The screen will blank and the blue LED will light.
You now have ten seconds to take your shot.
Operate your flash trigger and SDM will instantly detect USB has gone low and continue with the paused shooting sequence.
After an unknown but very repeatable delay of a few tens of msecs, the photo will be taken.
In SDM Stereo menu, if you set camera position to 'L' (for left) you can fire the camera's flash at 1/16 power.
A simple slave flash can detect that and then trigger your external flash.

The point is .. even though there is a delay it only varies by a fraction of a msec.
Occasionally, it will be outside that range.

This is very interesting, I am sure we can get it to work.


David
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Offline Microfunguy

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Re: Another USB shutter question...
« Reply #4 on: 26 / August / 2009, 17:33:18 »
I do not have software to draw a schematic so maybe Anaglyphic can do this.
Basically, we need a set-reset latch made from a 5V DIL relay with two sets of changeover contacts.
Pressing a switch would ground the relay coil causing it to operate.
One set of n/o contacts connected across the switch would close, keeping the relay held-in when the switch is released.

The current through those relay contacts would reach ground via a transistor (or two).

The one msec pulse from the flash controller would turn-off the transistor, de-energising the relay.
The other set of relay contacts would switch +5V to the USB connector.


David
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Offline CMC68

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Re: Another USB shutter question...
« Reply #5 on: 27 / August / 2009, 09:04:02 »
David,

many thanks for your reply. Sounds promising.

I'm not too worried about whether I use CHDK or SDM (in fact SDM seems suitable as Kapping is on the cards, but I'm having trouble with it on my mac - question posted on the Yahoo group).

Delay isn't much of an issue as long as it is repeatable. I can allow for that.

And I have slaves.

Just my electronics knowledge lets me down so if someone can do an idiots guide schematic that would be great (I can build a circuit if the instructions are clear, just not design one).

Here's hoping as as you say I think it is an interesting one.

Chris
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Offline Microfunguy

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Re: Another USB shutter question...
« Reply #6 on: 27 / August / 2009, 10:11:44 »
Quote from: CMC68 on 27 / August / 2009, 09:04:02
Sounds promising.
It will work and the delay will be repeatable.

Quote
SDM seems suitable as Kapping is on the cards, but I'm having trouble with it on my mac - question posted on the Yahoo group).

Your question has been answered by a couple of people.
You do not unpack DISKBOOT.BIN and you should also download Common_files.zip.


Quote
And I have slaves.

I have four of the Vivitar 283's with a control box that lets me dial-down the duration to 1/30,000.

Quote
Just my electronics knowledge lets me down


What we need is a simple transistor set/reset flip-flop like this one  : http://bowdenshobbycircuits.info/page9.htm

You would have a button connected from ground to the left transistor base.
That transistor collector is connected to USB V+.

The positive-going output from your flash trigger would go to the base of an NPN transistor via a 10K resistor.
The emitter connected to ground and the collector to the base of the other transistor.

Press the button, +5V switched to USB, screen blanks, blue LED lit, capture sequence paused.

Do your action and trigger the sensor ... negative pulse on right transistor base causes left transistor to turn on and collector voltage drops.

Capture sequence continues and after maybe 20 ms its internal flash fires.
Your slave immediately triggers the Vivitar 283's.


and there we are   :)

If I have time I will construct the circuit later.


David
« Last Edit: 27 / August / 2009, 10:14:48 by Microfunguy »
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Offline CMC68

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Re: Another USB shutter question...
« Reply #7 on: 27 / August / 2009, 12:41:30 »
Thanks David,

I've seen the replies on yahoo and am working on it now, I'll get there.

I have two 283s but just use a paper-clip to force it onto the lowest power setting (I also have a Nikon sb600 which I use sometimes). I'm looking at it as the flash duration not being an issue though if I am able to get a reasonably fast shutter. The flash can overlap the shutter if needs be. That then lets me shoot with ambient light and opens up new creative opportunities.

Quote from: Microfunguy on 27 / August / 2009, 10:11:44

What we need is a simple transistor set/reset flip-flop like this one  : http://bowdenshobbycircuits.info/page9.htm

You would have a button connected from ground to the left transistor base.
That transistor collector is connected to USB V+.

The positive-going output from your flash trigger would go to the base of an NPN transistor via a 10K resistor.
The emitter connected to ground and the collector to the base of the other transistor.

Press the button, +5V switched to USB, screen blanks, blue LED lit, capture sequence paused.

Do your action and trigger the sensor ... negative pulse on right transistor base causes left transistor to turn on and collector voltage drops.

Capture sequence continues and after maybe 20 ms its internal flash fires.
Your slave immediately triggers the Vivitar 283's.


and there we are   :)

If I have time I will construct the circuit later.


David


Sounds simple! ??? Appreciate your help.

Chris
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Offline Microfunguy

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Re: Another USB shutter question...
« Reply #8 on: 27 / August / 2009, 14:40:40 »
Quote from: CMC68 on 27 / August / 2009, 12:41:30
Sounds simple! ??? Appreciate your help.

OK, I have built it and it works.
I will try the flash later when it is dark.

First, you have to build the circuit.
Taking the link I gave as reference,  this is what I used :

Transistors (3)  - BC547
Left collector resistor - 2K7
Right collector resistor - 270R in series with high-efficiency red LED
Base resistors (2) - 22K

Connect normally-open switch from left transistor base to ground.
Connect right transistor base to collector of third transistor.
Connect third transistor base to ground via 1K8 resistor.
Connect third transistor emitter to ground.
Connect third transistor base to V+ via a normally-open switch and 2K7 resistor.

The component values are not critical, whatever you have that is reasonably close.


When you are ready, I can tell you how to test.


David

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Offline CMC68

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Re: Another USB shutter question...
« Reply #9 on: 28 / August / 2009, 04:02:00 »
Thanks David,

I've ordered the components. I'll come back once they arrive and I glue them together!

Chris
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