Detailed explanation of binocular camera synchronization signal interface: achieving precise exposure alignment of left and right images

In applications such as 3D depth perception, robot SLAM, mobile AGV navigation, unmanned aerial vehicle surveying, and industrial online inspection, binocular cameras rely on left and right view disparity to calculate 3D information. If there is a time difference between the exposure start time of the left and right imaging sensors, the object will have a positional deviation in the image, causing distortion in parallax calculation. Under high-speed motion conditions, this error will be further amplified.

To achieve precise alignment of binocular images, timing control is mainly achieved through synchronous signal interfaces. Different synchronization interfaces have significant differences in synchronization accuracy, wiring methods, transmission distance, and anti-interference capabilities. Reasonable selection of synchronization interface scheme is the key to ensuring stable and reliable output of binocular depth data. This article systematically sorts out the commonly used synchronization signal interface types for binocular cameras, analyzes the principles and engineering application boundaries of various solutions.

This type of signal is directly connected to the image sensor, which is the basis for achieving master-slave synchronization inside the module. It is usually led out through FPC cables and serves as the underlying signal for binocular hard synchronization.

FSYNC and FSIN are the core signals for binocular hard synchronization, with FSIN as the trigger input and FSYNC as the frame synchronization output, relying on pulse edge control to initiate sensor exposure. The project generally adopts a master-slave architecture: the main camera outputs FSYNC pulses, and the secondary camera is connected to FSIN to receive trigger signals, achieving synchronous exposure of left and right sensors with synchronization accuracy up to microseconds. The signal levels are commonly 1.8V and 3.3V, which are the preferred synchronization schemes for global exposure binocular modules.

Distinguishing point: FSYNC directly controls exposure triggering, with higher priority than VSYNC, and is the core signal for high-precision depth acquisition.

VSYNC marks the starting position of the image frame and outputs a pulse once per frame. Can be used for image frame timestamp alignment and also supports external output of synchronous reference signals. However, VSYNC only represents the beginning of frame data output and cannot directly control the exposure time. It is mainly used for auxiliary timing calibration and is not used as the main synchronization signal for binocular exposure.

HSYNC is a single row pixel data synchronization signal used for internal timing analysis of image data streams, and is generally not used for exposure synchronization between binocular cameras.

The sensor outputs an effective level during the exposure stage, mainly used for synchronizing external laser fill light and strobe LED light sources. It can also be used as a synchronization state reference signal and is widely used in structured light binocular solutions.

Implementing TTL pulse signals based on general-purpose GPIO, divided into Sync-IN synchronous input and Sync-OUT synchronous output. The main control outputs trigger pulses to synchronously drive the left and right cameras, supporting multiple sets of binocular module level networking. The industrial version can add optocoupler isolation, support 0-24V wide voltage input, and enhance anti-interference ability under complex working conditions on site.

Mass production of binocular modules will lead synchronous signals to standardized connectors for easy integration of the entire machine. Different connectors are suitable for different application scenarios

The mainstream choices for industrial binocular, mobile robot, and AGV scenarios. Pin integration SYNC IN, SYNC OUT, power supply GND， Excellent shielding performance, vibration resistance, suitable for hard synchronous wiring at the device end.

Industrial Ethernet dual target interface, integrating Trigger input/output and power supply, commonly used for workshop inspection and visual measurement binocular devices.

Long distance transmission binocular solution, AUX channel carries independent synchronous trigger signals, supports star and string type multi camera networking, and is suitable for long line bundle installation scenarios.

Embedded binocular commonly used interface, independently leading out SYNC IN, SYNC OUT, GND, easy wiring and debugging, suitable for prototype development and rapid verification.

The MIPI CSI embedded module solution directly extracts FSYNC and GPIO synchronization signals from the ribbon pins, with a compact size that is suitable for robots, drones, and IPC miniaturized binocular devices.

In long-distance transmission scenarios, SerDes chips can embed synchronous timing within image data lines, reducing the number of external wiring harnesses.

The SerDes transmission link can carry synchronous clocks while retaining independent pins to trigger FSYNC signals, balancing long-distance transmission and synchronization reliability.

The MIPI CSI-2 channel is only responsible for transmitting pixel image data, and exposure triggering still requires a separate FSYNC/GPIO hardware line to be led out; The new generation of long-distance MIPI scheme supports long-distance transmission and comes with a timing synchronization mechanism.

Important reminder: Embedded synchronization belongs to the timing transmission method. If microsecond level exposure alignment is required, hardware triggering pulses are still needed.

The network port binocular camera can adopt PTP precise time protocol, relying on network cables to achieve multi camera timestamp alignment.

Advantages: No need to install additional synchronization signal lines, making it easy to deploy multiple camera networks;

Shortcoming: Only achieving timestamp alignment, not hardware synchronization triggering exposure, with synchronization accuracy of tens of microseconds. High speed motion scenes are prone to depth errors and are more suitable for static detection scenes. High speed SLAM and 3D measurement of moving objects are not recommended.

1.Rolling shutter binocular module, most scenes do not require hardware FSYNC, relying on software timestamp alignment; **When using global shutter binocular for high-precision depth measurement, FSYNC hard pulse synchronization must be adopted.

2.Wiring design: Synchronous signal routing requires common ground; Long line transmission prioritizes differential signals or optocoupler isolation triggering to reduce synchronous jitter caused by electromagnetic interference.

3.Level selection: The sensor die level ismostly 1.8V, and the module GPIO commonly uses 3.3V; the industrial isolation version supports a wide voltage input of 0-24V.

There is no universal solution for binocular synchronization interface, and the selection needs to be comprehensively evaluated based on the application scenario. Static detection scenarios can use PTP network time synchronization; For high-precision scenarios such as robots, drones, and high-speed 3D measurement, FSYNC hardware pulse synchronization is preferred. Based on the transmission distance, vibration environment, and wiring cost of the entire machine, coupled with an adapted physical interface, it can maximize the stability and low error output of binocular depth data, fully leveraging the performance advantages of binocular vision in the field of 3D perception.