Hardware System Architecture
The Time Sync Board developed by InfiniteSense is a high-precision, low-latency time synchronization hardware module designed for multi-sensor systems (such as cameras, IMU, LiDAR, radar, etc.), suitable for autonomous driving, robot perception, surveying and mapping systems, industrial automation, and other scenarios. Through centralized control and time alignment mechanisms, this Sync Board ensures that data from different sensor types have unified timestamps, significantly improving data fusion accuracy and system consistency.
- Five channels of configurable-frequency homologous PWM trigger signals
- Two channels of PPS output for LiDAR/external IMU sync signals
- One channel of PPS input for GPS sync signal
- 12V power input, usable for industrial camera power supply
- Optional Ethernet/Serial port for host computer communication
- Built-in ICM-42688P gyroscope chip
- Dual-core Arm Cortex-M0+ architecture, main frequency up to 133MHz
- Equipped with 264KB SRAM, rich DMA support, flexible clock management, suitable for precision control and high-speed data processing
- Multiple independent I/O channels, flexibly configurable GPIO, interrupts, and peripheral communication, greatly enhancing sensor interface compatibility
The Sync Board is equipped with a MEMS gyroscope, capable of meeting the needs of most visual SLAM systems, effectively compensating for degradation of visual or LiDAR information. The ICM42688 is a high-performance 6-axis MEMS motion sensor launched by TDK InvenSense, integrating a 3-axis accelerometer and 3-axis gyroscope, suitable for AR/VR, drones, smartphones, wearable devices, and other applications.
Official Datasheet: ICM-42688-P Datasheet
To improve the time synchronization accuracy between the onboard system and the host computer, efficient and stable communication is essential. Therefore, we use the W5500 chip to build a 100/10M high-speed Ethernet communication interface. The W5500 is a full-hardware TCP/IP embedded Ethernet controller, providing an easier internet connectivity solution for embedded systems. The W5500 integrates the TCP/IP protocol stack, 10/100M Ethernet data link layer (MAC), and physical layer (PHY), allowing users to expand network connectivity in their applications using a single chip.
Official Datasheet: W5500 Datasheet
To power some sensors, this product integrates simple power conversion functionality, but is only suitable for low-power devices for convenient wiring.
- Supply voltage: 12V
- Internal power: < 1 W
- External sensor power supply: 5V @ 0.2A
- External sensor power supply: 3.3V @ 0.1 A
- External sensor power supply: 12V @ 1A
PWM signals can be used to trigger devices such as cameras and external IMUs. Any device supporting rising-edge triggering can use the proposed PWM interface for synchronization. Five different IOs are used to generate PWM waves, so each channel can be independently configured with different trigger frequencies to meet the needs of different sensors.
Typical PWM output interfaces include the four interfaces shown in the figure:
Where:
- VIN_O is floating by default; only with additional modification will the input power be directly forwarded here
- GND is the reference ground for the PWM signal
- 3.3V_O is the 3.3V output voltage, capable of providing up to 0.3W of power for simple devices. Please do not exceed this limit
- CAM_TRIGGER is the trigger signal, with the rising edge considered the trigger signal by default
Therefore, for any device requiring external triggering, GND and CAM_TRIGGER must be connected. The provided 3.3V and VIN_O interfaces need to be selectively connected based on your device's power supply situation.
To more intuitively display the trigger signal status, several additional LED lights are connected to the trigger signals.
When the trigger signal is high, the LED is off; when the trigger signal is low, the LED is on. Therefore, during the LED transition from on to off, the trigger signal produces a rising edge.
Many devices are designed to receive the PPS signal generated by GPS as the time synchronization source, such as most LiDARs and some industrial IMUs. Therefore, we designed two PPS signal output interfaces, generating TTL-level serial port data that simulates GPS time information sent to sensors, achieving timestamp synchronization functionality.
As shown in the figure, the PPS output interface includes four connections:
- PPS_OUT is the pulse-per-second output signal, triggered on the rising edge at 1Hz frequency
- GND is the reference ground for all output signals
- TX is the TTL-level time information transmission interface, sending timestamp information at 1Hz frequency after the pulse-per-second signal
- RX is unused, a reserved interface
Therefore, for any external sensor supporting PPS input, only three wires need to be connected: pulse-per-second, ground, and serial port signal.
!!! Some devices only support RS-483 or RS-232 level serial data, requiring the additional purchase of a level conversion module to use
To better visualize the PPS output status, 3 LEDs are used to monitor the pulse-per-second signal and serial signal status, as shown in the figure below.
Therefore, when the PPS output signal is normally generated, the PPS_LED1 light will blink at 1Hz frequency.
GPS/GNSS receivers typically serve both as sensors and as the time synchronization reference outputting PPS signals. Therefore, the designed Time Sync Board has the functionality to receive PPS signals, obtaining the reference time from GPS and then distributing it to various sensors to unify timestamps.
As shown in the figure below, the PPS input interface has 6 connections:
Where:
- PPS_IN is the pulse-per-second input interface, triggered at 1Hz frequency
- RX is the TTL-level serial port receive interface, obtaining raw GPS data
- TX is unused, a reserved interface
- 3V3 is the 3.3V power output interface, power < 0.3 W
- GND is the common reference ground for power and signals
- 5V is the 5V power output interface, power < 1W
Similarly, to visualize the PPS signal input, three LED lights are used to monitor signal status:
Therefore, after connecting GPS, when the PPS input signal is normally generated, the PPS_LED2 light will blink at 1Hz frequency.
The USB Type-C USB 2.0 interface is used for downloading programs and as a virtual serial port for communication with the host computer.
A standard 100Mbps Ethernet port is used for more efficient and stable communication with the host computer. Only after connecting the Ethernet cable and restarting will the Sync Board automatically use the network for data transmission.
The Sync Board includes multiple LED status indicators. Status indicators include system status indication, sync status indication, trigger status indication, transmission status indication, etc.
- System Status LED: Blinks rapidly when the system is running normally
- Sync Status LED: Blinks at a certain frequency, which is the sync frequency with the host
- Trigger Status LED: Blinks at a certain frequency, which is the set trigger frequency
- Transmission Status LED: Blinks at a certain frequency when data is being transmitted
In the PWM trigger interface, a nominal 12V interface is provided for powering industrial cameras, but this functionality is disabled by default. Some Ethernet industrial cameras require 12V power. For wiring convenience, our board provides a passthrough, directly forwarding the input 12V power to the PWM trigger interface, facilitating multi-camera wiring. To enable the forwarding functionality, locate an unsoldered resistor position on the back of the Sync Board, as shown in the figure below:
In the default shipped board, this resistor is not soldered for power safety. If you need to enable this feature, please solder it yourself or simply short it. The input power will then be forwarded to the PWM trigger interface, enabling industrial camera power supply.
- Power input accepts wide voltage input, 10-24V can all be used as input, but 12V input is recommended
- The output power of 3.3V and 5V is relatively low, unsuitable for powering high-power sensors
- Connecting high voltage to any IO port will burn the chip