The Las Vegas Boulevard Tracker Interface
Howard Long G6LVB
Abstract
Described is a satellite tracking rotator interface with the benefits of reasonable price, simplicity of construction and the flexibility of optional modules
Introduction
There are many rotator interfaces available for the Yaesu/Kenpro G5400/5500/5600 series of rotators, but in general many of them suffer from one of more restrictions.
Analysis of common current rotator interfaces shows that they all have drawbacks of one kind or another.
The purpose of the LVB Tracker is to provide a reasonably priced, user programmable and upgradeable interface, providing up-to-date standard hardware and software interfaces, backwards compatibility, and compatibility with a large range of prediction software.
Examples of Existing Tracker Interfaces
The Kansas City Tracker is an ISA card but it is very difficult to locate motherboards with ISA slots. The KCT tuner option also does not directly support some of the new radios recently becoming available. It is a PC-only documented proprietary interface.
The FODTrack interface has the benefit of being extremely cheap. It is a homebrew interface costing barely $25 to construct. It has a documented proprietary interface and many prediction packages support it. It has the drawback of only being a unidirectional interface, so it is not possible for prediction software to identify stalls. It relies on a hardware standard printer port. Newer Windows OS’s demand that direct access to printer ports is managed through a kernel layer driver which can significantly add to the complexity of designing interfaces.
The UNITRAC 2000 interface is developed and supported by ZL2AMD and provides a proprietary printer port interface. It also provides a radio tuning interface supporting most past and current radios with computer control.
The W0LMD SatTracker Jr. provides a standard Easycomm I or Novacomm interface over RS-232. The SatTracker Jr. interface is a unidirectional interface. The Easycomm I protocol is a very widely supported protocol.
The Yaesu GS-232A is a bidirectional RS-232 device offering a documented interface widely supported by many prediction packages. Its main disadvantage is the cost of the interface.
The LVB Tracker
Taking into account the issues surrounding existing trackers, for a couple of years the author has contemplated the possibility of providing backwards software and hardware compatibility, but simultaneously supporting newer interfaces such as USB and at a reasonable price. Simplicity of construction was also at the forefront of any design decision, with the aim of being no more complicated than a FODTrack to construct.
For more advanced construction, there are also several options available such as an LCD display and configuration buttons, or the option to choose between USB or RS-232 and maintain backwards compatibility with existing software. Because the unit uses a microcontroller, of prime concern was also the provision for the user to be able to program the unit without the need of a programmer.
With this in mind, the LVB Tracker was born. The heart of the tracker is the PIC16F876 microcontroller, including A/D converters, a bidirectional asynchronous serial port, in-circuit programming,
The FODTrack interface is so simple that a microcontroller is not used. This simplicity means that there is no requirement to program the FODTrack unit. Often, constructors are put off implementing microcontroller applications because of the requirement for a costly programmer. The LVB Tracker incorporates the programmer as an integral part of the unit. By changing three jumpers on the LVB Tracker, it is possible to use the tracker’s computer interface for programming purposes, so a programmer is not required.
When later software updates become available, the LVB Tracker can simply be switched into programmer mode and the updates programmed directly.
More and more predominant are USB interfaces. The LVB Tracker may use either a standard RS-232 connection or a USB interface. If the USB interface is chosen, when connected to the computer and the appropriate USB drivers are installed, the LVB Tracker appears as a standard RS-232 serial port despite it being a USB connection. This allows existing software packages such as Wisp and Nova to be used. USB drivers are available for Windows 98, ME, 2000 and XP, Mac OS-8, OS-9 and OS-X as well as being built into Linux, Open BSD and Free BSD.
For the software protocol, LVB Track supports subsets of the two most common interface protocols: the Yaesu GS-232 and Easycomm I/II. The firmware automatically switches protocols and automatically responds in the appropriate format.
Calibration settings are stored in EEPROM within the microcontroller. Typical settings include the A/D values at the end stops.
The optional LCD and optional pushbuttons allow the operator to see the rotator status and configure the unit without using a terminal emulator.
Practical Implementation
The LVB Tracker uses a fairly standard PIC16F876 implementation. The only slightly novel approach is that if the constructor chooses a USB interface, then the FTDI USB-Serial converter evaluation board is used. For the RS-232 interface, a standard MAX232 chip is used for level conversion. Both use the on chip USART and thus the same firmware.
The FTDI USB/Serial converter module is pre-fabricated using a standard 28 pin 0.1” pitch, 0.6” width DIL package. Although more expensive than using the 32 pin LQFP package, for ease of construction for the amateur the pre-fabricated module was used.
The device is powered from the Yaesu rotator interface.
One issue with building a device using a microcontroller is that the constructor needs to have the equipment to program the device. By using switches (implemented using headers on the PCB), the USB or RS-232 port may be used to program the device without any need for an external programmer.
Firmware
The firmware includes sufficient to be able to handle the A/D converters, the RS-232/USB communications and command string parsing, as well as the optional LCD and push switches.
Initial configuration such as setting the limit values for the calibration of the A/D converters may be done by either the push switches and LCD, or through the RS-232/USB using a terminal emulator.
The firmware is written entirely in Knusden Data’s C. This was chosen primarily because of its integrated floating point library.
Future options
By implementing the on-chip PWM function and adding appropriate high current motor drivers, it is possible to implement variable speed DC motor control.
Fabrication of PCBs would also enable many other constructors to implement the design without having to resort to point to point wiring.
Conclusion
The LVB Tracker is the result of a couple of years’ thinking and about four weeks actual doing. It’s a project the author has been meaning to start for quite a while and finally it has come to fruition. The name ‘Las Vegas Boulevard Tracker’ was chosen not only because it happens to fit the author’s callsign, but also many of the original design goals were developed by the author in Las Vegas.
With the open architecture and choice of design of the LVB Tracker, it will allow others to implement a satellite antenna tracking interface at extremely low cost but simultaneously provide the highest versatility and compatibility of any interface.
Completed prototype
Configured for RS-232 interface
For USB, the DLP-USB232M device is used
Point to point wiring on the prototype
Block diagram of the LVB Tracker
Circuit diagram of the LVB Tracker