Embedded Acquisition and Timing Controller

The embedded controller module is responsible for acquiring timing information from the existing CHARTS system, and correlating this time data with each frame of image data from the CMOS camera. This controller has an internal timer with high precision that will be correlated to the absolute time received from the onboard CHARTS GPS. The Applanix POS AV IMU unit in the main CHARTS enclosure sends out a TTL pulse (1PPS) once per second on a coaxial cable. It then transmits absolute time on the RS-232 serial “diff” port nominally within about 0.5 seconds after the 1PPS pulse. This serial data comes off the main CHARTS enclosure on the “CASI 1500” connector. Currently a cable connects this connector to the “BSP1” connector on the main CASI computer. We will remove the cable from the BSP1 connector, attach a Y cable between this connector and BSP1, and attach the other end of the Y cable to a serial port on our embedded controller. We will “T” off a coaxial cable from the CHARTS 1PPS signal to the embedded controller, as well.

In operation, the embedded controller will receive a pulse on the 1PPS connector each second. The controller will then look for valid timing data (TM1B) on the serial connector and will read in the 52 byte time data for each 1PPS pulse. This time data will be correlated to the embedded controller’s internal timer. The CMOS camera sends a pulse to the embedded controller each time a frame is acquired. The embedded controller will send internal timer information to the main data collection computer that will be attached with frame data that comes over the Firewire interface. In this way, the absolute time of capture for every frame of visual data is known. This time information will be used to associate visual pixel data with lidar data in post processing.