[Elphel-support] (Continuous) LED light trigger signal

[Andrey Filippov]

Andreas,

Short flash is definitely better (if that will not bother too much
humans - operator and/or other people), you'll save a lot of energy
and if you can get it really short (>10 ms) - you will not suffer from
motion blur.
For delaying lamp - I would recommend you to try some laboratory delay
generator, then make a simple circuit - there are so many ways how to
do that. Even analog one-shot with a potentiometer should do the job,
to be on the safe side (to protect the cameras) you can put an
opto-coupler on the input - the camera trigger pulse is 5V amplitude
and drives up to 1A, so it is easy to connect optocoupler input in
parallel to the other cameras,

Andrey

On Fri, Mar 16, 2012 at 1:21 PM, Andreas Bean <office at beanbox.com> wrote:
> Andrey,
>
> Earlier we talked about using the LEDs as "snapshot shutter" versus
> continuously lighting the scence.
> At the moment we have 2x100W LEDs on the cam, but I think that will not
> be enough to have snapshot functionality for panoramic indoor frames.
> What do you think?
>
> So I'm thinking that it will be better to continuously light the scene
> for 70ms during the exposure of the first to the last line.
> In that case I don't need any delay, do I?
>
> What kind of circuit to you propose to get the trigger to the LEDs not
> corrupting the camera timestamp sync?
>
> Andreas
>
>
> Andrey Filippov schrieb:
>> Andreas,
>>
>> I think that modulated signal will still trigger your flash, that
>> should not be a problem. With the single connector - the easies would
>> probably be to add an external delay before the flash for 70 ms.
>> Cameras have programmable delays between trigger and input and
>> starting acquisition, but here you need  the cameras to start 70 ms
>> earlier than the flash - they need  this time to erase each line.  So
>> you are correct - exposure should be at least frame readout time +
>> flash time, and  the flash should be triggered with the frame readout
>> time delay. It is possible to tweak the FPGA code and use the other
>> set of sync signals (small flex cable connectors inside the camera)
>> and add external connector, but that is not done yet.
>>
>> Andrey
>>
>> On Fri, Mar 16, 2012 at 9:00 AM, Andreas Bean <office at beanbox.com> wrote:
>>
>>> Andrey,
>>>
>>> Three days ago I got our two 100W led lighting modules for our panoramic
>>> camera.
>>> The trigger is a 0 - 5V signal against GND.
>>>
>>> Whats the easiest option to connect the modules to the camera? The
>>> trigger turns on the leds for 80ms.
>>> If I remember correctly then 70ms + exposure time is needed due to the
>>> rolling shutter.
>>>
>>> I'm not sure if its a good idea to use the camera sync port, since we
>>> already connected two cameras
>>> together. Also the timestamp is sent via that port, so it can't be a
>>> simple trigger signal.
>>>
>>> Whats the best option to get the leds triggered?
>>>
>>> Andreas
>>>
>>>
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>>>
>>
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>
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