Prop pitch style or custom antenna rotation motors need an azimuth indicator and control. Typically, selsyns or simple controls have been used for this purpose. In this article, K8CU describes his custom design that uses an embedded controller and touch screen LCD panel.

This antenna controller is the latest in a series of evolutionary controls I have used for my antenna rotators. My earlier control methods included simple hardware counters and LED direction controls.

These worked but lacked refinement. I then designed a universal antenna direction controller.

It has been in use since 1994 and has worked well for me. It is an essential station accessory, and a joy to use.

Circuit Description

This antenna rotor control consists of:

• Embedded micro-controller

• Graphics LCD display and touch screen matrix

• Tower mounted motor interface

This Hitachi or Zilog HD64180 embedded microcontroller runs at 12 MHz. Program memory is in an EPROM, and a Maxim RAM with internal battery maintains the data memory. Two serial ports are available, with either RS-232 or RS-485 supported.

A special purpose Seiko LSI controller provides LCD drive signals. This design has 64K of static RAM for LCD graphics. A hardware watchdog monitors the main CPU and generates a controller reset if an error condition develops.

I/O ports connected to the external interface use a board mounted connector.

Externally, two small relays for rotator direction control and a signal conditioner and optical isolator reside on the little interface board located near the main controller circuit board.

Inside the touch screen antenna rotor controller

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The graphics LCD display mounts on the enclosure front panel. This display is an attractive blue color, and the viewing angle and brightness are excellent. It is internally illuminated by cold cathode lamps that are driven by a high frequency lamp driver that is located on the embedded controller circuit board. This LCD is a graphics only display, and is organized as 256 wide by 128 pixels high. Immediately in front of this graphics array is a unique touch screen circuit. It consists of a grid of nearly invisible "wires" arranged as an X-Y matrix. Touching the panel results in the "wires" making contact that corresponds to the X-Y position of your finger.

A total of 64 separate touch locations are defined. There is no sound or physical indication associated with this. When the LCD is turned off and is not illuminated, a faint line can be seen where each "wire" is located. During operation, nothing is visible and it looks just like a normal LCD.

To implement a front panel switch or control, the program draws LCD graphics to surround a particular X-Y position where one of the "wire" grids is located.This results in a clean front panel that is easily customized for changing applications. Text or buttons can be placed anywhere. This is a universal smart control panel, customized by the software. The software is written in machine assembly language, and all displays are bit mapped graphics.

The original commercial application for this touch panel controller had the embedded controller circuit board mounted directly behind the LCD panel. The circuit board and LCD panel are about the same size, so normally it's a neat package. The box I wanted to use wasn't tall enough to allow this, so I remotely mounted the computer board and attached the two together with some ribbon cables. I also built a simple DC power supply adequate for my rotor motor and placed it in the enclosure. Nothing gets hot so ventilation isn't a problem. 

Main Activity Screen of the Direction Control 

Front panel controls are designed for simplicity. To turn the rotor to 135 degrees, I enter 1 3 5 Go. The panel indicator then displays the present direction as it changes and the selected heading. To stop the rotation anytime, I press Stop. A fixed time delay is built into the software to allow large antennas time to completely stop before another directional change is allowed. To use the control as a manual rotator, the Left and Right Arrow buttons are used. Six preset headings named Australia, Europe, Asia, Africa, etc. are available for general antenna pointing. A special Long Path button is pressed to turn the antenna to the long path heading of the currently selected azimuth. A Setup button selects more screen menus for other functions. A real time clock date and time display set for UTC is also shown on the main activity screen.

Additional LCD screens programmed into the controller allow for:

• setting up the specific motor gear reduction ratio

• setting the time and date of the internal real time clock

• North or South centered operation

• specific antenna directions for six common preset locations (Africa, Asia, Europe, etc).

• direction calibration

• a full keyboard screen is implemented
  
  

Click on small screen for larger photo.

Motor Interface

I use this controller with a prop pitch style rotor that turns my rotating tower and antennas. The photograph shows the open motor with the protective covering removed.  The tower mounted motor interface consists of a single transistor sized Hall effect component that sends pulse information from the main motor shaft. One turn of the high speed motor shaft sends one pulse to the controller located inside the ham station. Small 3-conductor cable is all that is necessary to add to the existing rotor wiring. I use common "one pair with ground shield" audio cable. One wire has five volts for power, one is ground, and the third is the pulse signal.

A small magnet is glued to a nut that is threaded onto the high speed motor shaft. This magnet rotates past the Hall effect device, which generates one pulse. The controller counts these pulses as a method of knowing the angular distance traveled. Since real motors coast after removal of power, the software keeps track of this. The Hall Effect device is built into hardware store small brass compression fittings and then covered with a potting compound. This assembly fastens to a motor bolt with two set screws.

The Hall Effect switch need not be built inside the protective brass fittings if it is securely mounted and protected. I chose this method because it can be changed quickly as a complete assembly.

High resolution antenna pointing is possible. The higher the motor ratio, the greater the resolution. The motor ratio I use is 9576, and the RTS rotating tower has a further two to one reduction, so the total motor ratio is 19152 to one.

Magnet and Hall Effect Assembly                 Hall Effect Device    

The newest part number now available for the sensor is Digikey # 480-5197-ND. I glued them inside a right angle brass compression fitting and then mounted it to the motor end on a spare bolt post. The magnet is glued to a nut that threads onto the high speed motor shaft. This gives one pulse per motor revolution. The assembled device is held to the prop-motor post by two small Allen set screws. Works like a champ!

Rotators that will work with this control:

It works where access to the high speed motor shaft is available. The output relays will directly connect across the two direction levers or switches in an existing rotor control box. Some rotors like the HyGain have a wedge brake that needs a separate control. The brake needs to be activated before turning, and the brake release needs to be delayed when rotation has stopped. This controller has spare outputs, and the necessary software changes to implement this wedge brake control are possible. A home made or custom rotor¹ should interface perfectly. This control will work for any rotor if you can add a Hall effect switch and a small magnet to the high speed motor shaft.

Multiple rotors on separate towers using this single control box are possible with a hardware and software upgrade.

Maintenance Issues

I have had trouble from lightning strikes taking out the interface that fits directly on the motor shaft. This costs a couple of dollars, and is not hard to change. It has been replaced three times in eight years. These are 5-volt Hall Effect switches sitting on the end of a long control cable that acts like an antenna. The lightning protection devices I have tried affected the output circuitry of the Hall Effect switch, and prevented proper operation. I use water-proof Molex connectors on this device to allow fast exchange should the need arise. This signal line is optically coupled at the station control end. This has prevented lightning damage in the control box. The power leads going to the motor also require lightning protection measures.

Adequate protection of the Hall effect signal cable has proven necessary. Suddenly, the antenna would rotate, but no signal direction information was available. An inspection of the cable near the tower base revealed the problem. Apparently one of the dogs had been chewing on it!

Notes

1.  Victor Mozarowski, VE3AIA, "Turning That Big Array" , Ham Radio Magazine, June, 1986. Pg. 10-15.    This is recommended reading as a basis for building a large rotor at home. The control box and direction indicator are basic, but the home builder needing a large rotor is presented with an option to the prop pitch.