Hi everyone; back again after a long spell. As usual, things have been busy. Plus I spent some time recovering some of my older posts that were corrupted when I moved the blog from CSEs web site to this location a couple of years ago. If you are interested in the posts on measuring pipe surface temperatures, both permanently and for a temporary data logger deployment, both of those are back in usable form again.
Meanwhile, Thursday evening, I was talking with one of the PEC Existing Building Commissioning workshop class students after class about relays, ladder diagrams and relay logic. Even though new construction projects typically use DDC controls, relays and relay logic are still out there in legacy systems and in buildings were DDC controls have been “value engineered” out of the project.
And, relays are frequently used to interface the low voltage DDC control circuits to the high voltage control circuits in the equipment they serve. So, knowing something about them and how relay logic works is a handy skill to have out in the field, even now in the age of computer based control systems
In the course of the conversation, we talked about how much you can learn by simply trying your hand at something. I also mentioned building a Jeopardy game that used relay logic. That got me to thinking that maybe folks out there would be interested in doing that as a way to learn about relay logic and ladder diagrams; hence the title of the post.
First, a bit of history (i.e. why I built a Jeopardy game in the first place). Steve Golden, my brother-in-law has a gift for oratory, people, and trivia that has been a blessing to the family on many fronts. For one thing, Kathy and I (and others after us) asked him to marry us, which he did with an eloquence and personal insight that I am sure nobody else could have matched.
But truth be told, what makes him a legend in the family is his ability to put together Jeopardy games based on family history. These games are in high demand at any family gathering. And, given the family size, there can easily be 50 or 60 people present if all of the brothers, sisters, nephews, nieces, aunts, uncles, etc. show up, so the game is played by teams and can get quite lively.
As a result, one of the problems when the Jeopardy games were played was to figure out who was first with an answer; Steve would read his question and with-in seconds the room would be filled with a chorus of “I know” from multiple members of multiple teams, leaving Steve with the task of deciding who was first.
So, I decided to solve that problem by building a little electric “gizmo” (as Kathy would say) that determined who was first via the push of a button, the result of which is show in in the picture at the top of the post. The gizmo would use relays and relay logic to:
- Turn on a light for the first team to push their button.
- Lock out the lights of the other teams.
- Sound a chime.
- Allow the game organizer to sound a buzzer, unlock the lights, and let the teams keep trying if a wrong answer was given.
So, I opened sat down with my Auto CAD Light software and came up with a circuit design that I thought would work.
If you click on any of the images, higher resolution versions will open up in a separate window and you can save them to your computer.
Then, off I went to my shop to scrounge up some relays and wire (yes, I actually had spare relays sitting around from back in the olden days). A quick trip to Radio Shack filled in the missing items in the parts list leaving only the issue of playing the Jeopardy theme song. We solved that while shopping for toys for the grandkids at Finnegan’s Toys, a really cool toy store in Downtown Portland.
Once I had all the parts and pieces, all I needed to do was wire everything up and test it. The drawings above reflect a few changes I made as a result of the testing and should produce a working game if you want to try you hand at it. Here are a few pictures of the wiring in mine to give you a feel for what that looks like.
So, that should be enough to get you started if you want to design and build your own version of the game for your family holiday party. Not only will you have a fun activity, you will likely learn a bit about relays, wiring, and relay logic, all useful skills if you are doing field work in buildings.
Of coursed, be careful as you work since the light portion of the system operates on 120 vac. The fuses and door interlocks are important safety mechanisms, so I recommend including them in any design you arrive at.
Feel free to use my drawings and pictures as a starting point. Like I said, my game works for us when wired as shown, but there may be features you want for yours that are not reflected in my design. For instances maybe you want multiple buttons for each team so that any team member can trigger the light, not just the team leader. That’s one option we are considering for our game; not sure if I will get it down in time for the party in a couple of weeks.
But no matter what, I know we will have a blast playing Steve’s latest version of Jeopardy at our family Christmas gathering.
I’ll try to put together another post with some more technically focused information on ladder diagrams and ladder logic, including an example of how you would “read” my Jeopardy game ladder diagram. Meanwhile, happy game building.
Senior Engineer – Facility Dynamics Engineering