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Could the camera shutter trigger be made available through I2C?

asked 2014-01-20 19:14:09 +0200

IZ1IVA gravatar image

updated 2015-03-31 15:55:49 +0200

I was wondering whether it might be possibile to relay the camera shutter triggering state through the I2C bus. The aim it to trigger external flashes/strobes while shooting Jolla's camera, for example.

Combining this feature with a modified TOH, it might also be possible to build a ring-flash like this: http://www.kickstarter.com/projects/brickandpixel/lightstrap-flash-and-video-light-for-iphone?ref=live

There should be an option in the camera app to turn this trigger on or off, but first of all I'd like to know if I2C is the right way to implement it... and of course if that might be of interest!

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"if I2C is the right way": there are no other option so yes it is the only way, using an I2C IO expander for ex. I don't know how synchronisation with the camera can be done (how long does it take to take a photo after the shutter is pressed).

zeta ( 2014-01-20 23:42:08 +0200 )edit

Yes, I2C is the only exposed bus, but I don't know how does it work and if it can carry this signal. Synchronisation might be a complex trial-and-error affair or just a matter of few simple lines of code, I have no idea unfortunately...

IZ1IVA ( 2014-01-21 11:07:47 +0200 )edit

Yes it can work, you only need an IO expander for that. For video where there is only on/off of the light, it is straightforward to do. For a real xenon-type flash which has to be synchronised with the camera shutter, I don't know the timing to respect, so can't say, but should be possible.

zeta ( 2014-01-22 00:38:49 +0200 )edit

after reading the "lightstrap" capabilities again : using a PWM expander, or better a led driver, with some RGB leds, you could control from the camera app the light level and its color (virtually any color).

zeta ( 2014-01-22 00:47:02 +0200 )edit

Yes, timing is crucial, but it has to be linked to the shutter rather than the camera's flash. This is because it's a LED (so long duration of the lighting), not a real xenon lamp (brief burst of light). And you're right, it'll be wonderful to adjust the colour temperature from the camera app!

IZ1IVA ( 2014-01-22 10:49:27 +0200 )edit

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answered 2015-03-30 18:05:47 +0200

r0kk3rz gravatar image

From an I2C perspective, you can create a TOH with LEDs which the phone can control, for example LeTOH.

The trick is to get the shutter state from the camera or camera app, which because of them being LEDs you don't need to be super accurate just enough for them to be on whilst the autofocus processes and takes the picture.

This would be easily done with your own camera app to go with the TOH, but a little trickier if you wanted it to work with any camera app

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Agreed, but I would like to also be able to trigger real flashes/strobes, not just LEDs. A ring LED TOH will be a great improvement, though!

IZ1IVA ( 2015-03-31 11:23:22 +0200 )edit

I2C would be fine for triggering and is low latency enough to be useful for that kind of purpose

r0kk3rz ( 2015-03-31 13:12:57 +0200 )edit

Great @r0kk3rz, I hope some developers would like the idea and implement it!

IZ1IVA ( 2015-03-31 15:53:44 +0200 )edit
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Asked: 2014-01-20 19:14:09 +0200

Seen: 414 times

Last updated: Mar 31 '15