LYNX Manual RA02
2.5
EXTERNAL TRIGGER
In the normal mode of operation, the camera is free running. Using the external
trigger mode allows the camera to be synchronized to an external timing pulse.
There are two general modes available for external triggering – software and
hardware.
In hardware triggering mode the camera receives the trigger signal coming from
the connector located on the back of the camera. The hardware trigger input is
optically isolated from the rest of the camera hardware - Figure 2.37. The input
signals “+ TRIGGER IN” and “– TRIGGER IN” are used to connect to an
external trigger source. On the edge of the external pulse which creates a positive
voltage difference between “+ TRIGGER IN” and “– TRIGGER IN”, a trigger
signal is sent to the camera. The voltage difference between the trigger inputs “+
TRIGGER IN” and “– TRIGGER IN” must be positive between 3.3 and 5.0 volts.
To limit the input current a 300 ohm internal resistor is used, but the total
maximum current MUST NOT exceed 25 mA. The actual trigger pulse duration
does not affect the integration time. The integration time for the first frame is
determined by the Pre-Exposure register – refer to the ‘spe’ command. The
minimum duration of the trigger pulse is 100 microseconds. There are no
restrictions for the maximum pulse duration, but it is recommended that the
trigger pulse is kept as short as possible, especially if a series of pulses are used.
In software triggering mode the camera receives the trigger signal coming from
the frame grabber via camera control signal CC1. In this mode, the exposure time
for the first frame can be programmed to operate in two ways:
1. The integration time for the first frame is determined by the
value programmed in the re Exposure register.
2. The integration time for the first frame is determined by the
duration of the actual CC1 trigger pulse.
Both the hardware and software triggering modes support three sub-modes of
triggering – 1) standard, 2) rapid capture and 3) double exposure. When the
camera is programmed to operate in either of the external trigger modes, the
camera switches from free running operation to an idle mode and waits for an
external pulse. The camera behavior for the different sub-modes is described
below.
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