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Usb control on a Canon D20

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Offline John Stilton

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Usb control on a Canon D20
« on: 12 / August / 2014, 10:41:50 »
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Hey folks,

I ordered two Canon D20 to make simultanous photos with a USB control. I'll install the cameras at the top end of 3m aluminium pipe, both facing in opposite directions. Beside other technical issues - I will have to deal with once the cameras arrive - I ask myself if there is a chance to get a response signal whenever a picture is taken.

I read that one is able to sync a number of cameras which sounds appealing for my application. But anyways, I would like to know from the ground whether the 10s interval has been exceeded or not. I imagine, sometimes a picture is taken within a second, sometimes it takes some seconds. Either way, I would like to know when that happens, to not wait in vain or not proceed to early... I think an accoustic signal could be superimposed by environmental noise. Any ideas? Or has this been discussed elsewhere?

Background is: I'd like to map a reach of a stream for scientific reason, resurveying every half a year to study changes in channel morphology taking a picture let's say every 5 meters.

Thanks in advance,
Yours John
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Offline reyalp

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Re: Usb control on a Canon D20
« Reply #1 on: 12 / August / 2014, 17:52:24 »
Quote from: John Stilton on 12 / August / 2014, 10:41:50
I ask myself if there is a chance to get a response signal whenever a picture is taken.

I read that one is able to sync a number of cameras which sounds appealing for my application. But anyways, I would like to know from the ground whether the 10s interval has been exceeded or not. I imagine, sometimes a picture is taken within a second, sometimes it takes some seconds. Either way, I would like to know when that happens, to not wait in vain or not proceed to early... I think an accoustic signal could be superimposed by environmental noise. Any ideas? Or has this been discussed elsewhere?
I wouldn't expect completely failed shots to happen very frequently. In full auto mode these cameras will sometimes refuse to shoot if they can't get focus, but otherwise they pretty much shoot when you press the button. There are some additional problems you can run into if you are using CHDK script.

If you want to make sure every shot is acceptable you'll  probably need to look at them after shooting, although that will depend on the environment.

The only outputs that you have easy control of from CHDK is LEDs and sounds. You won't be able to see camera LEDs from the ground, but you could probably rig up something with a photodiode. The D20 looks like it only has an AF led and one status LED.

It sound like in your situation the AF assist probably wouldn't be needed (3 meters is pretty far, and your subject is presumably quite a bit further), so you might be able to use that.

The status LED will show the normal Canon firmware status activity. That might be enough to tell if the shot was taken, but if it's like my D10, it's actually a couple different color LEDs. In that case, a single photo diode wouldn't give you the same information.

Alternately, if you want to go totally overboard you could use http://chdk.wikia.com/wiki/PTP_Extension live view to have a remote display on the other end of the pole ;)
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Offline John Stilton

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Re: Usb control on a Canon D20
« Reply #2 on: 18 / August / 2014, 08:05:09 »
[damn: if an attachement is too large and you press preview one's whole message text goes to Nirvana]

So, hello again.

Thanks for your reply. Very helpful. Actually, I like the idea of the mirrored screen. That would allow me to adjust the detail as well.

Regarding the LED: Actually I have an LED next to the On/Off switch. It flashes twice after a picture is taken. Sometimes it flashes once, by the way. Is there any way to transmit this information, let's say on the USB cable to the ground?

Attached my progress (not working so far).

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Offline reyalp

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Re: Usb control on a Canon D20
« Reply #3 on: 18 / August / 2014, 16:55:52 »
Quote from: John Stilton on 18 / August / 2014, 08:05:09
Thanks for your reply. Very helpful. Actually, I like the idea of the mirrored screen. That would allow me to adjust the detail as well.
If you are serious about this, you could theoretically do it with something like a netbook or a raspberry pi with a small external monitor. This would be a fairly involved project, but actually seeing the camera view in real time might be worth it.
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Regarding the LED: Actually I have an LED next to the On/Off switch. It flashes twice after a picture is taken. Sometimes it flashes once, by the way.
On my D10, this is actually a red and green LED, behind a single opening.
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Is there any way to transmit this information, let's say on the USB cable to the ground?
CHDK can't transmit information back of the USB cable unless it's connected to a USB host with PTP. If you have that, you don't need an LED. What I was suggesting a photo sensor taped over the LED, connected to a circuit that lights up a corresponding LED (or does something else) on the other end of your pole.
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Offline waterwingz

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Re: Usb control on a Canon D20
« Reply #4 on: 18 / August / 2014, 17:39:55 »
Quote from: reyalp on 18 / August / 2014, 16:55:52
What I was suggesting a photo sensor taped over the LED, connected to a circuit that lights up a corresponding LED (or does something else) on the other end of your pole.
With some careful attention to the optical coupling at the camera end, some fiber optic cable, and a lens with a diffuser plate at the other end,  you could maybe even make a passive device ?
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Offline reyalp

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Re: Usb control on a Canon D20
« Reply #5 on: 18 / August / 2014, 18:08:52 »
Quote from: waterwingz on 18 / August / 2014, 17:39:55
Quote from: reyalp on 18 / August / 2014, 16:55:52
What I was suggesting a photo sensor taped over the LED, connected to a circuit that lights up a corresponding LED (or does something else) on the other end of your pole.
With some careful attention to the optical coupling at the camera end, some fiber optic cable, and a lens with a diffuser plate at the other end,  you could maybe even make a passive device ?
I expect that would be pretty dim to use outdoors, the LEDs on my D10 are not very bright even looking at them directly. Unless maybe you used the AF LED.
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Offline waterwingz

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Re: Usb control on a Canon D20
« Reply #6 on: 18 / August / 2014, 18:11:34 »
Quote from: reyalp on 18 / August / 2014, 18:08:52
I expect that would be pretty dim to use outdoors, the LEDs on my D10 are not very bright even looking at them directly. Unless maybe you used the AF LED.
Yea .. unless when I said "pay attention to the coupling" that meant drill a little hole in the center of the LED lens and bond the fiber in with optical adhesive.   A little on the extreme side I realize.
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Offline John Stilton

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Re: Usb control on a Canon D20
« Reply #7 on: 20 / August / 2014, 03:28:40 »
Hm, I think this is not an option for me (both the optical coupling and the photoresistor). For now I will perform a test on how many fotos I lose without checking constantly. Additionally, I noticed that the camera has a GPS included, so in case of lost I'll still be able to assign fotos to its location!

Thanks for the good comments. It's a great community!

Yours,
John
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Offline waterwingz

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Re: Usb control on a Canon D20
« Reply #8 on: 20 / August / 2014, 08:01:24 »
Quote from: John Stilton on 20 / August / 2014, 03:28:40
For now I will perform a test on how many fotos I lose without checking constantly.
As reyalp pointed out,  the most likely reason to miss a shot is for the auto mode to refuse to shoot if it does not achieve focus lock.   If this proves to be a problem,  you could use a small script to monitor the USB  port and manage the shooting process manually.
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