Application Note: External Trigger & Flash

The Leutron Vision hardware products (PicPort^®/PicProdigy^® frame grabbers and the LVmPC system) together with Image Sequencer DRAL of the LV-SDS suite give the developer a powerful environment to build up a variety of applications acquiring images in real time into the host buffer. In addition, Leutron Vision offers a set of different cameras that do not require special cables to connect to the PicPort^®-Mono/Stereo grabbers even for special acquisition modes as asynchronous reset, frame integration, etc. With a single standard 12-pin Hirose-cable all these cameras may be connected.

Such applications must be able to control or communicate with external devices (such as external trigger or flash/strobe), synchronized to the video acquisition. They take advantage of frame grabbers' digital interface (optocoupler inputs and outputs) providing for such communication.

This application note gives you an overview of all aspects of such application design with Leutron Vision products. However, please refer also to the PicPort^® Getting Started Manual (PDF) and LV-SDS documentation (PDF) (especially Sequencer DRAL Programming and Reference Guide).

Frame Grabber's Digital Interface

All Leutron Vision frame grabbers provide optically isolated digital I/O interface for communication with external devices. The number of digital inputs and outputs is board-specific. The function of the first input optocoupler is defined as a trigger for image acquisition and it is reserved for use of the Sequencer DRAL. The function of the first output optocoupler (e.g. trigger, illumination control) depends on the selected Sequencer DRAL type and on the selected camera type. Additional optocouplers eventually available on the installed frame grabber are free for application use.

Digital I/O Connector

The optocoupler inputs and outputs are accessible from a dedicated internal connector on the board. This connector is a (blue) 16-pin 2.54mm terminal strip male connector for standard PCI and CompactPCI boards, and a (black or creamy) 40-pin terminal strip male connector for PMC frame grabbers. Position of the connectors is shown on the image below. The PicPort^®-Color frame grabber does not possess such connector, the optocoupler interface is accessible from its universal camera connector (HD-sub 44-pin female, details in PDF Getting Started Manual).

For convenience, Leutron Vision provides various cables (art number #14320, #14321, #14322) allowing to interface the digital I/O connectors from outside the case. These cables are terminated with a standard D-sub connector and it is up to the application developer to connect them with the external device(s).

The tables below describe the pinouts of the on-board's digital I/O connectors.

Frame grabbers for standard PCI bus and CompactPCI bus:

Frame grabbers for PMC form factor (including frame grabbers for LVmPC):

Digital I/O Internals

For use in industrial environment, the digital I/O signals are isolated by use of optocouplers. To take full profit of this signal isolation, you have to connect the optocoupler to an external power supply.

Variable 5V to 24V Optocoupler Interface

All the PMC boards and PCI PicPort^®-Color revision 6 and higher provide variable 5V to 24V optocoupler interface.

As you can see in the following drawing, the optocoupler input is prepared for input signals from 5 V to 24 V with the appropriate onboard serial resistors. The optooupler output is prepared for external voltage from 5 V to 24 V.

Fixed 5V or 24V Optocoupler Interface

The PCI/CompactPCI versions of PicPort^®-Mono/Stereo and older versions of PicPort^®-Color (up to revision 5) provide fixed 5V or 24V optocoupler interface.

As you can see in the following drawing, the optocoupler input is prepared for input signals of 5 V or 24 V with the appropriate onboard serial resistors. For other signal levels an additional serial resistor has to be added to guarantee the proper forward current. The optooupler output is prepared for external voltage of 5 V or 24 V.

Optocoupler Usage Examples

See also the following examples of optocoupler output. In industrial environment, signal levels of 24 V are usually needed.

Connecting External Devices

As mentioned above, the first input optocoupler of a board is reserved for image acquisition trigger in Image Sequencer DRAL applications. The first output optocoupler is reserved for illumination control (flash/strobe). Thus, you should connect your external device supplying acquisition triggers (if used) to the first input optocoupler of the board and the flash (if used) to the first output optocoupler. In case you are using multiple frame grabbers within a single Image Sequencer DRAL application, the external devices should be connected to the «master grabber». The decision which grabber will be used as master is done by means of software, see below.

Note 1: for PicProdigy^® boards, one optocoupler input is reserved for each sub-grabber (to be used as image acquisition trigger).

Note 2: interfacing the frame grabber's optocouplers, you are free to use either directly the on-board pin header connector, or the adapter cable ended with a D-sub connector. Both options are described above.

Hardware Configuration

Camera

Leutron Vision offers a set of different cameras that do not require special cables to connect to the PicPort^®-Mono/Stereo grabbers even for special acquisition modes as asynchronous reset, frame integration, etc. All these cameras may be connected with a single standard 12-pin Hirose cable. Thus the expensive cable manufacturing and difficult camera/grabber configuration handling may be avoided.

In case your application needs to acquire image sequences from multiple cameras, all of the cameras must be of the same type and running in same operating mode. To allow acquisition without any delays during the camera switching, the cameras should work in the «slave» mode, ie. accepting sync from the frame grabber so that their timing can be interlocked.

The camera(s) should be switched to the desired operating mode (eg. asynchronous reset), please refer to the camera manual for details. Also LV-SDS Camera Editor application can be a useful source of additional information. If you select proper camera type and press the «Info» button, you get a dialog that may contain important information, eg. about camera switches or available camera cables.

Part of the information in the dialog is specific to the normal (free running) mode of the camera. More asynchronous reset specific information is available in another dialog, invoked by pressing the «Async Reset» button. After selecting proper asynchronous reset mode (description in Software configuration chapter below) you are going to use, the «Info» button gives you information related to that mode (camera switches, possible constraints, etc.).

Frame Grabber

The frame grabber does not require any additional configuring. Please note only that in case of multiple frame grabbers in the system, the external trigger and flash (if used) should be connected to the master grabber. Furthermore, if your application needs to acquire image sequences from cameras connected to multiple grabbers without any delays during the camera switching, the grabbers' video timing must be synchronized by an external cable. Such cables (see the red line on the image below) are connected to frame grabber's universal camera connecor (15-pin D-sub). They are available as art no. #14440, #14441, #14442 (for 2, 3, 4 grabbers).

Software Configuration

Please note that the paragraphs below contain just the most important notes about the software configuration. Please refer to LV-SDS documantation (especially Image Sequencer DRAL Programming Guide, Image Sequencer DRAL Reference, and Camera Editor manual/help) for full details.

The asynchronous reset mode is not a standard acquisition mode, each camera implementing this functionality might require a different signal interface for triggering the acquisition. Furthermore, the same camera may provide different types of asynchronous reset (eg. with fixed or programmable shutter). The Leutron Vision Camera Editor provides a standardized interface for the definition of the asynchronous reset as implemented by each specific camera. More definitions are allowed for each camera type (eg. different definition for double speed mode, partial scan mode, or similar).

Furthermore, each definition may define various asynchronous reset modes. These definitions (named Mode 0 through Mode 7) are used by the DRAL libraries and they follow the asynchronous reset modes actually provided by the camera. The programmer has to specify proper mode when creating the DRAL object. See the image below, showing the Camera Editor's «Asynchronous reset settings» dialog. To learn the settings for individual modes, one has to select the mode using the «Camera mode» combo box - and the settings for selected mode will be displayed.

Among other points, the definition of each mode specifies shutter type (fixed/programmable), default shutter time, in case of programmable shutter the way how camera determines the shutter time (trigger pulse width, start-stop triggers, etc.), and more needed information. To get better overview of all the options, please refer to Camera Editor manual or help file.

Before initializing and starting the DRAL acquisition, various acquisition characteristics, well described in the documentation, have to be adjusted. One of them, mentioned several times throughout this document is the master grabber. In case of multiple grabbers involved in the task, the DRAL code runs on the master grabber, controlling all the other grabbers involved in the acquisition. Also the communication with external devices (trigger, flash) is performed by the master grabber.

The programming interface is in full detail described in the LV-SDS documentation mentioned by top of this chapter. It should explain the subject from programmer's point of view.