NEW PCB DESIGN AVAILABLE AS A KIT!.

 

The objectives that I followed when designed this rotor interface were simple: circuit complexity were not to be higher than the popular FODTrack design while providing higher resolution; control would be possible from a PC computer in a standarized format or from the front-panel of the interface; and there would exist a readout of the current positions of both rotors. On-the-run some features were added as they showed accesible. For example, digital calibration of the positon potentiometers eliminated the need for presets, you just tell the interface "this is North, this is South, this is horizontal, this is vertical" and it remembers everything.

 

From the hardware point of view resulted a simple circuit consisting of a PIC14000 microcontroller, a 24LC01 serial EEPROM memory, a 7805 voltage regulator, 4 opto-triacs, 4 triacs, 1 transistor, a 16x2 char. LCD display module and some discrete components. Take a look at the original circuit in PDF format

 

From the functional point of view a very reliable operation was obtained providing three modes selectable from the front panel: Remote, Manual and Calibration. In Remote mode information for rotor positions is received from a serial port in GS-232 or CI-V format at 4800baud. For the sake of mechanical protection the rotors are not allowed to go beyond preprogrammed limits in this mode. In Manual mode the rotor to be moved is toggled with one button and it is driven with other two. The LCD display is continuously updated with the current positions of both rotors. The electrical alignment of the system is performed in Calibration mode. The user programs reference positions for angle calculations, stop angles for mechanical protection and finally the amount of inertial movement of each rotor to increase pointing accuracy and prevent oscillations.

 

The GS-232 firmware version expects just a text line to be sent thru the serial port at 4800bauds consisting of the letter 'W', a 3 digit number representing azimuth value, a space character, a 3 digit number for elev. value and finally a carriage return character (0Dh).

 

The CI-V firmware version expects a set-frequency command (05h) with a destination address of DDh to be sent thru the CI-V bus at 4800bauds. It is like setting the frequency of any Icom rig, KHz for elevation and Hz for azimuth, ie. 180360Hz for an elev. of 180deg. and an azimuth of 360deg.

A note on resolution: Although the interface can operate up to tenths of degree and it displays angles with tenths, this level of resolution is not really useable with normal Ham equippment. This resolution is most often not even desired because of the high usage that mechanical parts would receive and thus limiting their life. Also normal antenna systems used by Hams seldom exhibit radiation patterns sharper than 10 degrees. In my station for example I use a modified Telex CD-45 II for Azimuth and a modified Alliance U-110. The CD-45's backlash is such that I have to set an inertial motion angle  of 3 deg. to prevent oscillations, for the U-110 I set 1.5 deg. Furthermore I configure the PC software to update the rotor's positions in 5 deg. increments, so we end up significantly far from the potential pointing resolution of 0.1 deg.!.

 

The high resolution capability of this interface is not easily exploited by most ham operators. Selected applications where this capability would be appreciated are EME, parabolic antenna aiming and any other high-gain highly-directive antenna system.

Other good reasons for using this interface are its 'self-contained' functionality -not depending on the host computer to keep rotors under control-, freedom from drivers to configure, ease of calibration, capability of being controlled from the same serial port as an Icom radio and last but not least, its low cost!.

 

original circuit in PDF format

 

Zipped source files of the GS-232 version.

Intel-HEX file of the GS-232 version.

 

Zipped source files of the CI-V version.

Intel-HEX file of the CI-V version.

 

Steve Blackmore has kindly made available his double-sided PCB design!:

PDF file including component placement overlay, component list and top and bottom PCB overlays

 

NEW!: Graham Langton developed a double-sided PCB design consisting of a main board and a front panel board. The two boards with plated holes and solder mask can be obtained from him for US$15. For a pre-programmed PIC14000 add US$20 to this price. Both prices include postage. Here is a PDF file fully describing Graham's design.

 

 

Fernando Mederos - CX6DD, Last updated december 2001.