Microwave Control Hardware Installation

To control our microwave dish we used easily obtained industry standard products and protocols to interface the Microwave Control Program to the dish. For the hardware we used the Opto22 Ethernet brain with binary output and analog input modules. Basically the program communicates using the Modbus protocol over Ethernet reading voltages from the analog input modules and turning the binary outputs on and off as needed. The analog inputs read signal strength from the microwave receiver and the voltage off the pan and tilt potentiometers. The binary outputs turn the pan and tilt motors on and off as needed to move, and set the frequencies and offsets in the microwave receiver.

The Opto22 equipment can be purchased directly from Opto22 at their web site: http://www.opto22.com. We chose the Opto22 as it supports Modbus over Ethernet. (More information on Modbus can be read from http://www.modbus.org.) The two software libraries that made this possible. The first is the low-level Modbus libraries developed on SourceForge.net at http://www.sourceforge.net/projects/jamod/. I basically downloaded the project and compiled it into a jar file JModbus.jar. The second part is a set of programming libraries that interfaced the JModbus.jar library to the Opto22 Ethernet Brain called MCLib.jar that can be downloaded from http://www.sourceforge.net/projects/maintmgr/. (These libraries are included in the installation packages and don't need to be downloaded separately.)

The first step was to build the microwave controller that was going to be in the satellite building by our satellite dishes and microwave tower. After purchasing the Opto22 with the requisite modules, we purchased a rack-mount drawer with power supplies and relays with a DIN rail mounting system. The voltages to drive the pan and tilt heads were 120 volts, but the binary outputs on the Opto22 were dry contact modules that only supported plus or minus 10 volts. In wiring up the binary outputs to the relays, Scott Nielson also wired it up in such a way as that if the pan clockwise relay was activated, it would make sure the counter-clockwise was disabled. (I tried to do the same thing in the software also.) One design change we had to make after implementing the system was to add a separate power supply to run the potentiometers. We found that when running the relays the power supply would dip just enough that the voltages read over the potentiometers showing pan and tilt position would be wrong. Here is a picture of the rack mount drawer with the Opto22, microwave dish on our tower, and the the BMC (Broadcast Microwave Services) microwave receiver:

Rack mount drawer with Opto22 Ethernet Brain showing integration with relays and power supplies. KTVX microwave tower with moveable dish on top. Microwave receiver in our satellite building next to the KTVX microwave tower.

If you look at the picture you will see one binary input module that we were originally going to use to see AFC lock, power to the pan/tilt heads and power to the receiver, but abandoned later as unnecessary.

One important thing we found with the Opto22 is that it needs good clean conditioned UPS power. Without clean power we found we had to power cycle the Opto22 daily. APC has a good SmartUPS that can run the power supplies and the Opto22. Purchase the size you need depending on what you connect to it.

Here are the part numbers of what we would order today from Opto22 if we were building this again from scratch.

Qty Description PN# Price* (each)
1 SNAP Analog/Digital/Serial Ethernet Brain SNAP-B3000-ENET $695
1 SNAP B-Series 8-Module Rack SNAP-B8M $94
1 SNAP Power Supply, 110 VAC to 5 VDC SNAP-PS5 $200
2 SNAP 2-Ch 0-250 V RMS AC/DC Analog Input Module SNAP-AIVRMS $195
3 SNAP 4-Ch Dry Contact Digital Output Module, Normally Open SNAP-ODC5R $45

*Prices valid as of 1/23/2003 from their web site.

The DIN rail and DIN components we purchased from Mouse at http://www.mouser.com. We basically wired in everything through the DIN connectors where everything was labeled. The rack mount drawer we purchased from Performance Audio at http://www.performanceaudio.com.

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