Hi again,

So I finally got the plans up on the site. The multi rotor control system was designed way back in 1987, before I was able to get schematic generation software etc. The plans are drawn by hand as best as I could do back then. The project was originally called the Rotor Switch.

This project describes a Multi Rotor Control System designed and installed in 1987 at the Concordia University Amateur Radio Club, CUARC (VE2CUA). It is still in operation today.

The club is situated in downtown Montreal in a "high rise" type building. The station was located on the 6th floor and the antennas were on the roof, approximately another 6 floors up. Most of the coax cables and rotor cables ran through a cable plenum and it was extremely difficult to run additional cables.

We already had an 8 conductor rotor cable, however we wanted to add two more rotors. One for the new HF beam; and another for a satellite rotor.

So we needed a way to use one or two rotor control heads in the shack and control all the antennas on the roof. Well, I came up with the design, built, tested and installed the unit in 8 weeks during my spare time (I had a full time job).

This design is many years old and relatively simple and robust. It does not use PICs, Software or firmware. It is just a hardwire logic type circuit and a bunch of relays (why get complicated?). The control system comprises a Rotor Selector Unit (RSU) in the shack and a Remote Relay Unit (RRU) on the roof. It is capable of connecting 2 Rotor control heads to 8 rotor motors.

It has been in operation for 15 years or so and I believe it only broke down once or twice and needed a few plug-in relays to be changed on the roof. Not bad for homebrew........

The situation above is probably similar to many other club stations so have fun and let me know the details of the system you built, so I can post it to the site and share your experience with the rest of the world.

This section describes the Rotor Switch schematic in detail. The design is old, but can be readily adapted to current technology. I present it here to stir some hobbyists and for general info. I have prepared the schematic in .PDF format page by page to ease downloading options.

This page describes the Rotor Switch system and interfaces. The system comprises two units; the Rotor Selector Unit (RSU) and the Remote Relay Unit (RRU).

The RSU can select between 2 rotor control heads (RCH A & RCH B-Not part of the design) and between 8 rotor motors. The control bus allows communication between the RSU and RRU and provides control signals through 5 wires. The rotor bus is essentially a connection between the rotor control heads (RCA&B) and the 8 rotors and can handle up to 8 wires.

The RSU comprises three sections, the logic section (control bus & display), Power supply section, and the rotor control head selection.

Power Supply section: This is a basic power supply; it converts 110 VAC to +5 VDC and +24 VDC. +5VDC is used for the RSU logic and +24 VDC for driving the control bus.

Logic Section: Selection of a rotor is accomplished by a 555 one shot driving a 0-7, 7490 counter. This counter drives a series of 2N2907A transistor line drivers. As well, the line drivers are adjustable to compensate for line losses from +5VDC to +24 VDC. This should allow location of the RRU up to 300 feet away from the RSU. The only constraint will be the actual rotor control head distance capability.

The 7490 counter also drives a 74138 demultiplexer that drives 8 LEDs indicating which rotor is in use. There is also a 555 timer configured to flash the LEDs. You can omit this circuit; but every new visitor to the concordia university shack always asks-What is that flashing light for? (Self promotion?)

Rotor Control Head Selection is accomplished by a relay.

The rear view shows the power cable, Rotor Control Head input A & B (8 Screw terminal strips). Rotor Bus output 8 Screw terminal strip and the control bus 5 screw terminal strip.

• Selects between two rotor control heads (A or B) through a SPST pushbutton switch
• Has one rotor bus output
• Has one control bus output
• Power ON/OFF switch ( SPST pushbutton)
• Rotor Select switch (Momentary pushputton switch)
• Rotor Selection Indicators.

This schematic shows a basic power supply providing +5VDC and +24 VDC. T1 was actually a 21 VAC unit, (i.e. it only had a single 21 VAC secondary). A single diode bridge and filter capacitor was used instead of the two shown. The regulators are standard positive LM7805 and LM 7824 3 terminal linear voltage regulators.

The LM 555 timer is configured as a one-shot pulse generator, with S1 being the Rotor Selector Switch. A square wave pulse is applied to the 7490 decade counter input. The counter provides a 3 digit binary code. This code is applied to the transistor line interface. The code is also applied to the 74138 demultiplexer. This component lights the corresponding LED. The 555 timer is configured as a flasher circuit to blink the LED rotor indicators. The 2N4126 transistor serves to stop the 555 timer during the counter pulse.

The Rotor Control Head Switch (S2) applies +5 VDC through some diodes driving the all the demultiplexer input signals high. This serves to automatically switch to Rotor position 1, when rotor control head A is selected. This was a safety feature, since there were many station operators, and there was a possibility that the wrong rotor control head would be used to control the wrong rotor, since not all rotors are wired the same way.

The binary code output from the 7490 counter is applied to inputs A,B and C. Two transistors were used in series to drive the 24 VDC relay coils and invert the logic. +24 VDC is applied to the relay coil/transistor collector. The diodes on the transistor bases and relay coils are 1N4002 rectifiers. A 10K ohm potentiometer was used to set the voltage of the line drivers-NOTE: This voltage should be set to a maximum of +5VDC at the RRU input-otherwise this could damage the RRU demultiplexer input. The relays connect the binary digits to the +24 VDC line through the potentiometer; hence you can have +24 VDC logic levels!!. The voltage is applied to A, B, and C logic levels on the control bus terminal strip. If the relay is not energized, the relay contacts short the control bus lines to ground minimizing noise pick-up. +24 VDC and a ground are also sent up the control bus to power the RRU.

The Rotor control switch connects +5VDC to the Control bus logic signals and drives the transistor/relays. The relays select between rotor control head A or B, and pass the signals through to the rotor bus output.

The RRU inputs are the Control bus and rotor bus. The control bus supplies power and logic signals. The rotor bus provides the rotor head control signals to control the rotor. These signals are passed through the relays and provide the RRU output.

The Control bus signals are filtered. +24VDC is sent to the relays and to an LM7805 +5VDC linear regulator. The control bus logic signals are sent to a demultiplexer and then to transistor relay drivers.

The RRU was housed in a plain aluminum box, approximately 10 inches wide, 4 inches deep and 14 inches high. It was not in a weatherproof box--the plain aluminum box was placed in an insulated box on the roof of the high rise building. The rotor control bus and the rotor bus input are at the top of the box and the rotor bus outputs are below. These are all screw type terminal strips. All relay wiring was done with 18 AWG stranded wire.

The control bus signals are filtered through chokes L1-L4 made from 15 Turns evenly spaced around an Amidon FB-43-2401 ferrite and C1-C3 & C4. NOTE: The RSU control signals must be adjusted to a maximum of +5VDC at the input of the RRU 74138 demultiplexer.

+24 VDC is applied to the relays and the +5 VDC LM7805 linear regulator--which supplies power to the 74138 demultiplexer.

The output of the demultiplexer is applied to the relay drivers (1-8).

Each terminal screw of the rotor bus (1-8) is connected to 8 relay contact inputs. This is the most tedious part of the whole project. Take the time to make your own wiring diagram and wire up one input terminal at a time. A mistake here will be really difficult to debug and correct due to the vast amount of wiring once completed.

A word about relays, I chose 24 VDC relays due to the low cost since I needed a bunch. I selected 4PDT, 2 amp contact type relays. Each relay had 4 contacts, so to switch 8 wires at a time I had to use 2 relays.

The demultiplexer outputs from page 10 are applied to the transistor line drivers (2N2222). There are 8 line drivers.

This is a neat project and has been in operation for 15 years.