10,000 Light Bulbs and 1 PLC Equals a Controls Engineer’s Christmas

Written By: Tim Maynard

With Christmas right around the corner, I can finally say this year’s lights display is complete.  Actually, I started acquiring new parts and lights last January because I was planning two big additions to the display for this year. The first was a rather large scrolling LED display, and the second was lighting up the roof using a remote I/O (input/output) rack to control it. However, I made several assumptions which proved wrong.

I purchased several GE 90/30 DC output cards, and I assumed my PLC, an IC693CPU350, would be fast enough to quickly refresh the display. I had built an LED matrix in college for my digital design course, so I got it out and added some resistors to drop the voltage from 12 volts to the 5 volts required by the matrix.  In total, it consisted of  six-5×7 LED matrix displays with the rows wired together and each column separate.

Matrix of LED Lights

I tested this back in August, but even at its fastest, the display only produced a headache-inducing flicker. Since I wasn’t able to get a faster PLC, I had to scrap the LED display. (So if anyone reading this happens to have an IC693CPU674 or an RX3I PLC from GE that you would like to see put to a good use, let me know.)

The second display I wanted to add this year were lights to the roof of the house. I had planned to add a remote I/O rack using an Automation Direct terminator I/O that communicated using Modbus TCP. To this end, I upgraded my Ethernet module in my PLC to one that was capable of communicating Modbus TCP. I also obtained an Automation Direct Ethernet module and two 1yo6-point relay output modules.

Controls Inputs and Outputs

I added the code to the PLC for communicating to the remote rack, but I was unable to get it to communicate properly. I kept getting a no response from module fault. I then looked up the documentation and found my problem. In my haste to get parts to test, I only saw that I had purchased an Ethernet module. I even checked the specs, and it said it would do Modbus TCP. I did, however, miss the part where it said only the new version would.

The T1H-EBC does not support Modbus, only a propriety standard from Automation Direct. The T1H-EBC 100 does support Modbus TCP as well as operating at 100 megabaud, but as I did not have the extra $267, I will have to wait until next year. What I did learn was the importance of testing and to test early. Had I done so, I would have had time to get another module.

In the midst of purchasing racks and modules from eBay, I also obtained two additional relay outputs, and I decided to add these to my existing PLC rack. I was going to use the extra outputs to operate the roof lights and the 18 outputs I didn’t use during last year’s display to run the additional lights I had purchased in January, but I again ran into a hardware issue.

Using all these modules required more power than my PLC power supply could source on the 5 volt backplane, so I was only able to add one additional module. I finally had to give up on the roof, so I guess out doing the house from National Lampoon’s Christmas Vacation will have to wait for another year.

However, I was able to overcome my biggest problem from last year thanks to Anixter sampling me a 75 foot, 20-conductor cable. With that addition, I was able to use the left over outputs from last year to add two more junction boxes on the northern side of the property to run a line of candy canes up the driveway and another junction box to run candy canes on the south side of the driveway. I was also able to better route my lights, making better use of my junction boxes and reducing the amount of extension cords used.

Most of what I learned from this year’s display, I already knew. It was, however, a refresher course in project management as well as a reminder to research the equipment you use and not put things off to the last minute. The display was the best I have ever done, and it was fun doing it. A lot of my friends enjoy seeing it, too, so I will put it down as a success and try for an even bigger display next year.

I will be building a new enclosure that will be installed in a fixed location, and I also need additional space for more racks. I will be getting the proper Ethernet module for my remote rack, so I can light the roof, and I will also be making a set of prints for everything to make it an easier setup from year to year.

Until next December, please enjoy a video of my 2012 Christmas lights display:

Also, a special thanks to the people and vendors who helped me this year:

  • Mark Harmeson – Bastian Solutions
  • Phil Donovan – Anxiter
  • Doug Ungru – Gexpro , Part of the General Electric Company
    • “GE – We bring good things to light.” (an old slogan that I thought was appropriate)
  • Kirby Risk Electrical Supply


Tim is a senior controls engineer at Bastian Solutions. He is a graduate of Purdue University and a former US Marine.

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