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

[Andrey Filippov]

Andreas,

Yes, you are right - I just did not think of that. If you can generate
rather constant brightness for 70+ ms, then you do not need any delay
and you do not need to have light much brighter than environment. The
duration of the light has to be readout time + exposure time (exposure
may be short), and the light should be triggered simultaneously with
the camera (or earlier - each camera delay is programmable). when the
camera is triggered it start exposure of the first line, at
exposure+readout time - finishes the exposure of the last. What
happens before first or after last - does not matter.

Andrey

On Fri, Mar 16, 2012 at 2:55 PM, Andreas Bean <office at beanbox.com> wrote:
> Andrey,
>
> Thanks for the description of the trigger pulse. An optocoupler is fine,
> I will do it that way. The module is controlled by a microcontroller, so
> we can set arbitrary delay times. But if I remember correctly, I need to
> set the exposure time to 67ms to use the flash as an shutter and the
> flash has to be much more brighter than the scene without flash.
>
> Lets say in an average room with two windows the leds may double or
> triple the brightness of the scene or even if the flash increases the
> intensity by a factor of ten.
>
> Our camera is helmet mounted. We have seen that during walking we can't
> go beyond 7ms exposure time without reasonable motion blur. From my
> point of view I can't set 67ms. Or am I missing something here?
>
> Andreas
>
> Andrey Filippov schrieb:
>> 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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>>>>> Support-list at support.elphel.com
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>>>>>
>>>>>
>>>>>
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>
>
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