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Chapter 2. ICL 17
3-Color Sequence
In this setup the target is illuminated by three filtered lights. Each light can be switched on and off almost
instantaneously (in less than a millisecond). There is a small amount of camera-triggered hardware logic that
coordinates the hardware with the exposure. All lights are turned off when the Shutter Closed Output pin is
on. The experiment resets and starts again when the Shutter Open Output pin goes high (and the first light
turns on). Then when the camera's Trigger Waiting Output pin goes high, the experiment switches to the next
light (cycling: red-green-blue).
The trigger port is being jumpered into itself. In other words, the Trigger Waiting Output is jumpered back
into the Trigger Level Input. (The Trigger Invert Level Input is jumpered to Ground.) The final result is that
(in the script below) the camera begins exposing while it waits for a trigger, then, it triggers itself. The Trigger
Waiting Output pin has a high signal on it for about 7 microseconds. When you see the high signal, switch to
the next light in the sequence (red-green-blue-red-green-blue-etc.).
All of the pins are standard TTL voltage levels, so the associated circuitry is fairly straightforward.
It is important to take this sequence as FAST as possible, so, use the CCD37-10 frame-transfer CCD (512x512
image size, 512x544 storage size) and readout one exposure, while exposing the next. Although the script
doesn't appear to expose at all (aside from the first image), the exposure time is equivalent to (readout time +
shift time), or about (140 + 1.2) 141 milliseconds.
script_begin();
shutter_open(); /* SIGNAL TO BEGIN THE EXPERIMENT */
clear_parallel(6); /* clear CCD of charge: 2.54 ms / clear */
expose(141); /* give proper exposure time for 1st image */
loop_begin(50); /* SEQUENCE OF 50 IMAGE TRIOs */
loop_begin(3); /* one trio */
shift_image_to_storage(); /* 1.23 millisec, leaves mode: shift_mode_s */
expose_until_trig(); /* CHANGE TO NEXT LIGHT (7 micro-sec pulse) */
shift(32); /* discard excess in CCD37-10 storage array */
pixel_readout(0,512,1,512,1);/* about 140 milli-sec at a speed of 2 MHz */
pixel_display( 512, 512 );/* this has no effect on the expose timing */
loop_end();
loop_end();
shutter_close(); /* SIGNAL EXPERIMENT END & RESET */
script_end(1); /* leave the CCD in continuous clear mode */