External trigger Camera Module2

Compared to ordinary camera modules and even other specialized imaging solutions, its advantages are concentrated in timing control, system integration, and scenario adaptability, specifically in four aspects:

1. Exceptional Timing Precision and Control: They enable the alignment of the image capture instant with the occurrence of an external event with microsecond-level accuracy. This is crucial for analyzing high-speed or transient phenomena. Users can precisely define the trigger logic and timing by designing external circuits, achieving absolute control over the capture moment.​
2. High Data Efficiency and System Performance: By capturing only "valuable" frames, they significantly reduce the generation of invalid data. This lowers the computational load on subsequent image processing units, saves storage space, and improves the overall processing throughput of the system.​
3. Powerful Multi-Camera Synchronization Capability: This is one of their most prominent advantages. In applications like 3D reconstruction and motion capture, a single master trigger signal can command dozens or even hundreds of cameras to expose simultaneously, ensuring all viewpoints capture the exact same moment in time and eliminating measurement errors caused by desynchronization.​
4. Enhanced System Integration and Reliability: They can be seamlessly integrated into automated systems composed of sensors, PLCs, and mechanical devices, acting as a responsive and reliable link within the control loop. The deterministic nature of hardware triggering makes it immune to PC software delays or operating system scheduling, providing the reliability required for industrial-grade applications.

Its working principle follows a "Trigger Signal Input → Signal Parsing → Capture Execution → Data Output" closed-loop process, with clear division of labor between hardware and software. The specific steps are as follows:

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Step 1: Generation of External Trigger Signal​

The trigger signal originates from an external device, and the type of signal depends on the application scenario:​

Hardware Trigger Signal: Generated by physical devices (e.g., proximity sensors send TTL pulses when detecting objects; encoders on conveyor belts send pulses per unit distance). These signals are transmitted to the camera module via dedicated hardware interfaces (e.g., GPIO pins, BNC connectors).​

Software Trigger Signal: Generated by upper-layer software (e.g., a PC's machine vision software sends a "capture command" via USB/I2C; an IoT gateway sends a trigger instruction via Ethernet). These signals are transmitted through standard communication protocols.​

Step 2: Signal Reception and Validation by the Camera Module​

The camera module's built-in trigger control unit (a dedicated chip or FPGA) receives the signal and performs two key validations:​

Signal Format Validation: Confirm the signal meets pre-configured parameters (e.g., TTL pulse width ≥2μs, rising/falling edge polarity matching; software command syntax compliance). Invalid signals are filtered out to avoid false triggers.​

Timing Adjustment (Optional): If the system requires a delay between signal reception and capture, the trigger control unit executes the pre-set "trigger delay" (adjustable from 0ms to 1s) before initiating the next step.​

Step 3: Initiation of Image Capture and Sensor Control​

After validation, the trigger control unit sends a "capture command" to the camera's image sensor:​

For global shutter sensors, the sensor captures the entire frame simultaneously to avoid motion blur.​

For rolling shutter sensors, the sensor starts scanning the image from top to bottom according to the trigger command.​

During capture, the module temporarily pauses other non-essential functions (e.g., preview) to ensure computing resources are focused on image acquisition.​

Step 4: Image Output and Post-Trigger Feedback​

Image Output: The captured image is processed by the module's ISP and then transmitted to the upper-layer system via interfaces like USB 3.0, MIPI CSI-2, or Ethernet.​

Feedback Signal (Optional): To realize closed-loop control, the module can send a "capture completion signal" to the external trigger source.