App Note: Using GPIO on LUCID Cameras

Many high precision applications using machine vision cameras require the camera to capture a frame at a precision instant (ie. When the target object moves into camera’s field of view) or multiple cameras to capture frames synchronously. This application note outlines the method available to trigger the camera to capture a single frame, a series of frames or synchronize multiple LUCID cameras to capture image or sequence of images together precisely for these applications.

The camera has three operation modes – Free-run or Stream Mode, single frame or Snapshot Mode and Trigger Mode.

The following section describes how to set LUCID camera(s) in Free-run Mode, Snapshot Mode and Trigger Mode.

• 1x LUCID Phoenix or 1x Triton Camera
• One GPIO cable for Phoenix or Triton
• Arena Software

In Free-run mode, the camera with the build in sensor produces a stream of images at a predefined acquisition frame rate continuously. The sensor captures one frame of image into the pixel array and transfers the pixel data over the sensor interface into the camera electronics. During this transfer, the sensor may capture the next frame of image. Under this mode, the exposure of the current frame may overlap with the readout of the previous frame.

In the above example, the camera free-runs at a fixed 20 frame per second without any external control over when exactly each frame is captured.

Unlike Free-run mode, Snapshot mode takes only one image. The software grabs one frame out of the Free-run stream and pass it to the application level. This mode is useful when the user only wants to capture one image at any time.

The software puts the camera in SingleFrame Acquisition Mode, snaps an image (AcquisitionStart cmd) and then pass that frame to the application for display. The framerate is undefined (shown as 0.0) as only one image was captured.

In an industrial environment, many applications need to capture an image at a given point in time. The use case could be object inspection, when the target object moves to the front of the camera, the application would need to take an image of the object at that precise moment. The host machine is often equipped with ability to output an electrical signal exactly when the object is passing in front of the lens of the camera.

This electrical signal generated by a device such as a photodetector is the key driver for the camera to start capture. When the camera is operating under this mode, it is said to be in trigger mode.

Note: When a rolling shutter sensor is triggered, the sensor needs to take and read out an extra frame to reset the sensor. This typically reduces the maximum achievable trigger frequency to about half of the maximum value of the AcquisitionFrameRate node on most rolling shutter cameras.

Power
We recommend to power LUCID cameras either via the camera’s Ethernet connector (PoE) or via the camera’s I/O connector.

• When using PoE, the power supply must comply with the IEEE 802.3af standard. You can find recommended parts to power the camera in LUCID web store.
• When powering via the GPIO, please use pin V_AUX(12-24V DC Power Input)

GPIO Connector
LUCID recommends using LUCID’s standard GPIO-8P20 and GPIO-M8 for Phoenix and Triton cameras’ I/O control.

To capture multiple images per trigger pulse, please stop the camera from acquisition and put it in the Burst mode:

In certain applications, other devices need to be synchronized with camera capture regardless of the camera’s operation mode (Freerun or Trigger). In this case, the user can take advantage of the strobe output function on the camera to know when exactly a frame capture is taking place. In the following section, strobe configuration is discussed.

For a list of resistor values and pull-up voltage values, please refer to the following table.

Instead of using an external trigger signal, the user can use a master camera’s strobe output to trigger one or many slave cameras to achieve synchronous capture.

In many high precision tasks, jitter and delay are two common characteristics system designers care about in order to guarantee a certain precision in their inspection task. Knowing the jitter and delay values helps the system designer to understand the accuracy in device operational sychronization.

To measure the jitter and delay of LUCID cameras, you can use an oscilloscope and two probes. Follow the steps below.

1. Set Exposure Auto to Off and Exposure Time to a fixed exposure time, such as 500µs .
2. Put the camera in trigger mode. Refer to Trigger Configuration section in the application note.
3. Configure strobe output on the camera. Refer to Setting Up Strobe Output section in the application note.
4. Attach a probe to your trigger signal pins and another probe to the camera’s strobe output pins.
5. On the scope, the trigger signal and strobe signal can be shown at the same time. Measure the difference between trigger activation edge and strobe output edge.

The following jitter and delay values were measured on specific camera models with specific firmware. These values may change depending on firmware version and mode of camera operation. Please refer to the value below for comparison with your actual setup.

LUCID has implemented a featured named Trigger Latency to allow more deterministic trigger behavior. When this feature is enabled, the trigger latency will be fixed and the jitter will be significantly smaller.

To turn on the feature, set Trigger Latency = One Line

With Trigger Latency set to One Line, the following measurements were captured on a PHX050S-PC (IMX250MZR): Trigger Latency is ~61 microseconds and Jitter is typically <100 nanoseconds.

There is no single solution of using GPIO that fits every application. The most suitable solution (ie. Using Optocoupled pin or not) depends on the application need. The following table shows a quick summary of optocoupled versus non-optocoupled input/output pins.