I/O Control: Hardware Triggering for Machine Vision Cameras and Lights
Gaspar van Elmbt
Industrial machine vision cameras are designed for precision, speed, and reliability. To maximize performance, the external triggering system must be equally robust. This guide explains how to ‘hardware trigger’ a machine vision camera using a trigger sensor, synchronize multiple cameras, and trigger external machine vision lighting.
Table of contents
1. How Hardware Triggering Works
When fast and accurate operation is required, the trigger sensor must react instantly. It functions by changing the voltage on specific pins of the camera’s I/O connector, signaling the camera to capture an image.
Trigger Signal Types: Rising Edge vs. Falling Edge
- Rising Edge: Voltage shifts from low to high, triggering an event.
- Falling Edge: Voltage shifts from high to low, triggering an event.
By using edge detection, the camera can respond quickly and accurately to trigger signals.
2. Configuring a Machine Vision Camera to Accept Hardware Triggers
Step 1: Activate Trigger Mode
Using the Galaxy SDK software, connect to the camera and set:
TriggerMode = On
Step 2: Select the Trigger Source
Software Trigger → Trigger by pressing the TriggerSoftware button.
Hardware Trigger → Select the input line where the trigger will be received, e.g., line0.
Step 3: Optimize Trigger Settings
Enhance the trigger response by adjusting parameters such as:
- Rising Edge / Falling Edge – Defines the trigger activation method.
- Trigger Delay – Adjusts timing between the signal and capture.
- Trigger Filters – Reduces unwanted noise interference.
3. Connecting a Trigger Sensor to a Machine Vision Camera
Example: Using a Retroreflective Sensor
In this setup, a retroreflective photo sensor (S100-PR-5-C10-PK) detects objects and sends a trigger signal to the camera. When an object interrupts the sensor’s reflected light beam, the camera’s input pin receives power, triggering image capture.
Example: Using a Foot Pedal Switch
A foot switch (FS-01) or any analog toggle switch (open/close circuit) can also be used as a trigger. Pressing the pedal closes the circuit, sending a signal to the camera.
4. Using a Machine Vision Camera to Trigger a Strobe Light
To trigger a light source, assign the camera’s strobe function to one of its output lines:
Define Line1 as an output
Set LineSource = Strobe
When the camera is ready to capture light, the strobe output will send a high-voltage signal. The signal will remain low when none or only a portion of the pixels are ready to capture light.
Considerations for Global vs. Rolling Shutter Cameras
Global Shutter: All pixels capture light simultaneously.
Rolling Shutter: Pixels capture sequentially; the strobe signal will activate after 1/framerate (e.g., 50 FPS → 20ms delay).
For rolling shutter cameras, the strobe signal will work only when the exposure time is greater than 1/framerate. Refer QuickStart: 5 steps to trigger LED from Vision Camera using strobe controller for more information.
5. Synchronizing Multiple Cameras (Master/Slave Setup)
Master-Slave Camera Triggering Example
Below is an example of a master camera being triggered by a photocell sensor, with a slave camera synchronized to the master.
When the trigger sensor is activated, it outputs a high voltage signal, causing Pin 1 of the master camera to also go high.
As soon as a rising edge is detected on Pin 1 of the master camera, the camera opens the connection between Pin 7 and Pin 8 once all pixels are ready to capture light. By default, Pins 7 and 8 are normally closed (NC).
Electrical Behavior:
When Pins 7 and 8 are closed:
The voltage on both pins is low and so, Pin 1 of the slave camera also remains low.
Then current flows from the 24V power supply, through a 1K resistor (for current limiting), then through Pin 8 and Pin 7 of the master camera, returning to the ground of the power supply.
When Pins 7 and 8 are open:
The voltage on Pin 7 remains low, while Pin 8 of the master camera goes high. Consequently, Pin 1 of the slave camera also goes high.
The current now flows from the 24V power supply, through the 1K resistor, then through Pin 1 of the slave camera, and finally back to the power supply ground via Pin 3 of the slave camera.
6. Triggering a Strobe Controller with a Machine Vision Camera
A machine - vision camera can also be used to trigger an external light source via a strobe controller. More information can be found here.
In this setup:
· The camera generates a trigger signal when capturing an image. This signal is sent to the strobe controller.
· Upon receiving the trigger, the strobe controller powers the LED light. The strobe output provides a high voltage signal when all cameras’ pixels are ready to capture light. (For global shutter camera, all pixels are ready simultaneously. For Rolling shutter cameras, there’s a delay of approximately 1/framerate before all pixels are ready.
· LED light is connected to the output of the strobe controller.
· An analog pedal switch is also connected to the camera’s input. This allows manual triggering of the camera, which in turn triggers the light source.
7. I/O Port Configurations & Voltage Considerations
When integrating an industrial machine vision camera, it's important to note the differences between GigE and USB3 camera pinouts:
- GigE Cameras: Offer the option to be powered via the I/O connector
- USB3 Cameras: Always rely on the USB bus voltage for power and cannot be powered through the I/O connector.
This distinction does not affect the schematics for triggering the camera but is essential when planning the power supply setup for your system.
Trigger Cable Connection
To connect a trigger cable to your camera, please refer to the MER2 GigE Camera I/O and MER2 USB3 Camera I/O manuals. You can download them from our Download Page.
8. Advanced Triggering Functions
We recommend using Line 0 as the camera input and Line 1 as the camera output. These lines are optically isolated, ensuring enhanced reliability and noise immunity.
Voltage Specifications: For Line 0 & Line 1 (Optically Isolated)
- Logic 0 (No Action): 0V – +2.5V
- Logic 1 (Action Triggered): +5V – +24V
Current Range: 7mA – 25mA | A current-limiting resistor is advised for voltages above 9V.
Voltage Specifications: For Line 2 & Line 3
For expanded functionality (if there is a need for multiple i/o), Line 2 and Line 3 can be configured as either inputs or outputs.
- Logic 0 (No Action): 0V – +0.6V
- Logic 1 (Action Triggered): +1.9V – +24V
Note: When configuring Line 2/3 as inputs, avoid pull-down resistors above 1KΩ, as they may cause the input voltage to exceed 0.6V, preventing proper detection of Logic 0. To prevent damage to GPIO pins, always connect the GND pin first before supplying power to Line 2/3.
9. Additional Triggering Features
Hardware triggering offers various features and options to improve the reliability and accuracy of your camera system:
- Rising/Falling Edge Delay: Defines the time required for the camera to confirm that a valid trigger signal has occurred.
- Frame Trigger Wait: Ensures the camera output remains high until it is ready to receive the next hardware trigger. This setting allows for the highest possible trigger rate.
- Input Debouncer: Filters out short-duration pulses by setting a minimum valid signal duration for both rising and falling edges. This helps eliminate false triggers caused by noise.
- Trigger Delay: Introduces a defined delay between the moment a trigger is confirmed and when the camera executes the trigger action.
- Input Inverter: Allows users to reverse the input signal logic by configuring the “LineInverter” setting.
10. Custom I/O Functions & RS232 Support
If your industrial camera application requires custom I/O functions, such as using GPIO for RS232
communication, we offer custom firmware solutions.
Need a Custom I/O Configuration?
Contact us today for tailored solutions to meet your specific requirements.
