Accurate USB remote sync for single camera shots? - Microfunguy's Builds - CHDK Forum
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Accurate USB remote sync for single camera shots?

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Offline fudgey

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Accurate USB remote sync for single camera shots?
« on: 03 / February / 2008, 09:48:05 »
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I've never tried the SDM build, but the new high-accuracy remote synchronization feature made me wonder whether it would be suitable for single camera use as well?

I took a look at http://stereo.jpn.org/eng/sdm/synch.htm#usb and got the impression that the SDM build is able to trigger the camera from USB cable detach after a delay which will be constant (with greater accuracy compared to the normal USB cable attach trigger) for every shot (at least until camera mode/settings are altered).

Even though the length of this delay is not known, it can be measured. If this delay really is constant, we can obviously take photos using electrical trigger signals that fire slightly before the desired time of the shot. Very usable especially for things that can be actuated electronically a bit after the USB trigger (like blowing things up in pro style), or (especially repetitive) phenomena that can be electronically sensed before the desired shooting moment (such as water dropping to ground from a distance).

Btw, has anyone measured whether placing a resistor in parallel to the camera's USB power inputs would speed the detach detection up (and also enhance accuracy of the sync) even further i.e. either tried it or alternatively measured how long it takes for the USB supply voltage of the camera to drop once the remote voltage has been disconnected?
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Offline crunchy_3d

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Re: Accurate USB remote sync for single camera shots?
« Reply #1 on: 03 / February / 2008, 10:18:24 »
Quote from: fudgey on 03 / February / 2008, 09:48:05
Even though the length of this delay is not known, it can be measured. If this delay really is constant, we can obviously take photos using electrical trigger signals that fire slightly before the desired time of the shot. Very usable especially for things that can be actuated electronically a bit after the USB trigger (like blowing things up in pro style), or (especially repetitive) phenomena that can be electronically sensed before the desired shooting moment (such as water dropping to ground from a distance).

Btw, has anyone measured whether placing a resistor in parallel to the camera's USB power inputs would speed the detach detection up (and also enhance accuracy of the sync) even further i.e. either tried it or alternatively measured how long it takes for the USB supply voltage of the camera to drop once the remote voltage has been disconnected?

SDM, as you have noticed, is not intended only for stereoscopic purpose, but also for accurate shooter triggering.

The delay between releasing USB voltage and shutter opening is 17ms for A640 (and is constant). Detection of releasing of USB voltage is instantaneous (probably within some microseconds). The times are also constant for A620 and A630, but they are not measured up to now. For S3is times are not constant but vary for about 40ms. Delay between releasing USB voltage and detection that the USBvoltage is dropped is from 37ms to 67ms (based on 5 measurements). Add additional 13ms from detection of USB voltage to shutter opening and you can see that S3is, in present stage, is not suitable for high-precision shots.
 
Concerning the resistor, there is no need to apply one, since the actual USB voltage drops immediately after releasing the button on A620 - A640 (the same holds for S3is).
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Offline crunchy_3d

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Re: Accurate USB remote sync for single camera shots?
« Reply #2 on: 03 / February / 2008, 10:22:39 »
Quote from: crunchy_3d on 03 / February / 2008, 10:18:24
The delay between releasing USB voltage and shutter opening is 17ms for A640 (and is constant).

I haven't defined word "constant". In most cases it is in a range +- 0.1ms. However, in some rare cases it happens that the time changes for +-1ms.
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Offline fudgey

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Re: Accurate USB remote sync for single camera shots?
« Reply #3 on: 03 / February / 2008, 10:54:28 »
OK that's just...great  :)

I have an a570is, I'm assuming nobody has measured it's behavior with the fast sync yet?

Also, can you think of a reason why this type of trigger couldn't be integrated into the other builds (allbest mostly I suppose) capable of USB triggering, maybe with an option to select trigger polarity (USB Vdd rise/fall, the latter being capable of accurate sync)?

Btw, has anyone thought of adding a common feature to all builds which would let the user to select a different build for the next boot by some creative renaming/moving of diskboot.bin, ps.fir and CHDK config files?
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Offline Microfunguy

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Re: Accurate USB remote sync for single camera shots?
« Reply #4 on: 03 / February / 2008, 11:02:03 »
Quote from: fudgey on 03 / February / 2008, 10:54:28
I have an a570is, I'm assuming nobody has measured it's behavior with the fast sync yet?


Well now  .........  all I had better say is that we hope to have results today  :)



David
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Offline crunchy_3d

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Re: Accurate USB remote sync for single camera shots?
« Reply #5 on: 03 / February / 2008, 11:05:08 »
Quote from: fudgey on 03 / February / 2008, 10:54:28
I have an a570is, I'm assuming nobody has measured it's behavior with the fast sync yet?

You can help if you have photo-transistor and oscilloscope. Just measure the time from releasing USB voltage to switching-off blue LED diode. If it's instantaneous, there is a great chance that you may use it for time-precision shooting.
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Offline fudgey

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Re: Accurate USB remote sync for single camera shots?
« Reply #6 on: 03 / February / 2008, 13:01:15 »
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You can help if you have photo-transistor and oscilloscope. Just measure the time from releasing USB voltage to switching-off blue LED diode. If it's instantaneous, there is a great chance that you may use it for time-precision shooting.

I do... will have to try that as soon as I can find a USB cable to butcher  ;)
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Offline fudgey

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Re: Accurate USB remote sync for single camera shots?
« Reply #7 on: 29 / February / 2008, 09:18:53 »
I finally found some time to test this, but I can't get remote sync to work on a570is (I have one camera, I'm still only trying to achieve accurate remote trigger timing).

I removed my old chdk.cfg, started SDM 1.4, enabled synchronization and tried the remote test script from http://stereo.jpn.org/eng/sdm/synch.htm#usb. The camera shoots every time I press my remote button down (enable 5V on USB), just like it does on the Allbest builds.

The blue light does blink but I'm not getting the only-shoot-after-usb-voltage-drops behavior I thought I was supposed to get with sync enabled (the red sync label is printed on the top of the LCD).

Am I missing something or is it just not working as it should?
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Offline crunchy_3d

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Re: Accurate USB remote sync for single camera shots?
« Reply #8 on: 29 / February / 2008, 16:37:44 »
Quote from: fudgey on 29 / February / 2008, 09:18:53
The camera shoots every time I press my remote button down (enable 5V on USB), just like it does on the Allbest builds.

The blue light does blink but I'm not getting the only-shoot-after-usb-voltage-drops behavior I thought I was supposed to get with sync enabled (the red sync label is printed on the top of the LCD).

Am I missing something or is it just not working as it should?

Strange... The reasons might be the following:

- the flash is switched on and pre-flash is firing. However, the actual picture is taken after releasing the button (with some smaller flash power)
- the option "Enable Synch" in Synchronisation Menu (Stereo) is not enabled

If this is not the case, have you cleared the card completely before loading SDM or initially testing the USB input with some higher voltages??

Which script are you using (synch.bas?)?

Damir
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Offline fudgey

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Re: Accurate USB remote sync for single camera shots?
« Reply #9 on: 29 / February / 2008, 17:07:18 »
Quote from: crunchy_3d on 29 / February / 2008, 16:37:44
Strange... The reasons might be the following:

- the flash is switched on and pre-flash is firing. However, the actual picture is taken after releasing the button (with some smaller flash power)
- the option "Enable Synch" in Synchronisation Menu (Stereo) is not enabled

Camera was in P mode with flash disabled, synch was definitely enabled.

Quote
If this is not the case, have you cleared the card completely before loading SDM or initially testing the USB input with some higher voltages??

No, I only replaced diskboot.bin and ps.fir and renamed chdk/chdk.cfg to another name to get a clean config for sdm. Are there other files which could mess it up?

I'm using a push button USB Vdd trigger with approx 5,1 VDC, current limited to about 150 mA at the moment. A single 3,3V lithium cell wasn't enough to trigger my a570is.

Quote
Which script are you using (synch.bas?)?

The simple remote test on top of the page I quoted, but I also tried synch.bas and syncl_L.bas with the same result.
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