Living south of downtown San Jose gives us a fantastic and regular view of aircraft on approach. Being a radar-systems engineer my natural reaction was “I must track them.” After months of searching for an affordable gimbal/servo-based positioning system, a night of star-gazing made the solution obvious. Log onto Ebay, wait four days and my $100 Meade antenna positioner arrived, complete with integrated servos and positional encoders.
Now I should state here, due to legal reasons, I have no intention of tracking the aircraft via radio waves. Instead I would like to test a video tracking system, which would augment a radar when the target object is low enough in elevation to cause multi-path issues for the radar. The cheapest and fastest path-forward was to utilize the Video Experimenter Board from Nootropic Design.
The electronics package consists of the Nootropic shield interfaced with and Arduino. To control the telescope positioner, the electronics package must communicate with the Autostar via RS232. An Amani GT is used to bridge between the Arduino UART and a Digilent Pmod232.
The Amani is also being used to handle an issue I am having with the video shield/Arduino stopping the video tracking arbitrarily. Serving as a watchdog, the Amani looks for a heartbeat signal and resets the Arduino when loss of heartbeat is detected.
Of course this configuration is just a method of rapid prototyping, for proof-of-concept and experimentation. The VTE issue must be ironed out eventually, however to get the tracking algorithm development going the Amani-reset will serve as a patch in the short-term.
Progress thus far has involved sitting the unit in the window and observing the video tracker’s ability to resolve and track aircraft while I steer the gimbal manually. With minor code revisions to the sketch provided at Nootripic Design, I was able to develop an error vector, seen below, which will serve as the input error to the tracking loop.
Currently I am ironing out the Autostar commands I found online, some if not most of which do not seem to work. If anything I’ll need to sniff the comms between the Astrofinder software on the PC and the Autostar. It should be noted that the PC software is not involved in this project and is just used for troubleshooting and communications study. A PC will be included in this system to provide graphical data to the user as well as a general control interface. The biggest issue I have is not being able to control speed. If necessary I’ll open the gimbal itself, cut into the motor controllers, and take control via the electronics unit.
I do have feed back from the positioner in the form of encoder counts, which is vital for closing the tracking loop. Currently I use the building across the way for boresiting the unit and calibrating the encoders.
The Meade ETX-60AT itself is a beginner’s telescope, better suited for terrestrial viewing. As it is integrated into the controller base, I cannot remove it without compromising the internal optics, thus it serves as platform for the camera to piggy-back on. It does open possibilities of integrating the telescope into the system, for distant-object tracking.
Even more interesting, and a definite DO NOT ATTEMPT, would be to integrate a laser range-finding system into the telescope while the camera provides the video tracking. This solution would provide fully-integrated TSPI data for under $400.
Check back for progress and project documentation.