Using Trigger and Digital I/Os - Part 2
Please Note: This blog post is part of a series of five posts altogether.
The posts include: Part 1, Part 2, Part 3, Part 4 and Part 5.
Trigger input - Hardware
The trigger input of The Imaging Source USB and FireWire CCD cameras is opto-coupled. It permits positive trigger pulses with any amplitude between 3.3 V and 12 V. If you intend to apply higher pulses, please make sure that the current lies in the range of 3 mA to 12 mA.
Trigger input - exposure and image readout timing
The Imaging Source USB and FireWire CCD cameras offer two different modes of operation:
Free running: The cameras generate a stream of up to 60 images/s depending on their resolution. To considerably reduce the amount of data, the frame rates may be reduced to 30, 15, 7.5 or 3.75 images/s. The exposure length is software adjustable in the range of 100 μs to 30 s. Please note, however, that the camera’s clock generator determines the actual moment of exposure. Thus, it is not controllable externally, but measurable using the strobe output. Therefore, this mode of operation is called “free running”.
Trigger: The cameras offer a trigger input to determine the moment of exposure. The exposure begins 4.8 μs after the occurrence of a trigger pulse. The exposure length is software adjustable from 100 μs to 30 s. The duration of the image readout is the reciprocal of the current frame rate. Once the image readout has finished, the camera is able to accept a new trigger pulse at any time.
(To be continued…)
Boris Tad said,
June 3, 2008 @ 22:49
Hi,
my experience with IS camera exposure settings shows that real exposure value update is delayed by approx. 0.5sec. It would be nice to have an exposure time set by a hardware through the length of the trigger pulse (100ms-30sec) instead.
regards
Boris Tad, engineer
LaSen, Inc.
Xiao Sun said,
June 4, 2008 @ 11:24
Hi Boris,
We understand your concern, but at the moment we do not have plans to implement such a mechanism of exposure time control.
Regards,
Xiao
Using the Trigger and Digital IOs of Imaging Source Cameras - unicap-imaging.org blog said,
June 9, 2008 @ 17:15
[...] gives some details about the hardware and explains how to build an external trigger circuit: Trigger Hardware and Timing Pin Header Layout Hirose Connector Layout Software support for this functionality is present in [...]
Milos said,
June 26, 2008 @ 16:28
If I understood it well I could use triggering if I need exact exposure moment for 25fps (with external clock), and in free running mode it would have some kind of rounding error? Right?
Stefan said,
June 27, 2008 @ 09:39
>If I understood it well I could use triggering if I need exact >exposure moment for 25fps (with external clock),
Yes, correct.
>and in free running mode it would have some kind of rounding error? >Right?
This is wrong. The frame rate is determined by the currently set frame rate as 60, 30, 15, 7.5, 3.75 fps. If the exposere time is longer than the currently used frame rate allows, then the frame rate is halfed until 3.75 fps are reached. After 3.75 fps are reached and the exposure time is longer, the frame rate is determined by the exposure time. That means, 2 seconds exposure time results in 0.5 fps.
Thus, the frame rate is not rounded anywhere.