Test & Measurement Automation

Custom Relay Circuit Board

Jesse Batsche: Hello, my name is Jesse Batsche. I'm a Project Manager here at the DMC, and this is my FedEx Day Project. It is a 32-channel custom relay circuit board made for switching connections and automated test applications. 

FedEx Day is a tradition that we've started at DMC over the past couple years where we will periodically have a day where the entire office takes a break from our normal project work and spends time working on projects that have a benefit to DMC or are fun projects that are engineering and technically related projects that are just cool applications of the technology that we normally work on here at DMC. And the goal, the reason it's called the FedEx Day project is because we have to deliver something the next day; like a FedEx delivery and have something to show and demonstrate from the previous day's progress to show the rest of the company the next day. Here is the 32-channel custom relay switching printed circuit board that I put together for DMC's recent FedEx Day. 

What this circuit board provides is 32 independent relays that can be used for a wide variety of purposes in both automation as well as automated test and measurement applications that DMC works on. Just having the ability to switch connections in an automated fashion is extremely useful and powerful for, again, a wide variety of applications. This might be switching power on and off to a particular device. It might be taking one highly accurate and perhaps expensive instrument and having the ability to switch the connections of that instrument's probes to a variety of points that you might want to acquire measurements on. So this kind of multi-flexing architecture makes it possible to design, test, and to have really accurate instrumentation but are cost effective because it can acquire all the measurements you need with a smaller set of instruments. 

The goals of this were really just to put something together that would allow us to do relay switching with some high electrical performance specifications, something that would be really easy to integrate into the platforms and stuff that we typically develop these automated test applications on. In most cases, that tends to be LabVIEW and using National Instruments hardware. 

I think we'll start with looking at the control of this system, and for this I chose to go with a NI compact DAQ chassis and to design the board to work with a C series module that provides 32 syncing digital outputs, basically that means 32 channels where, based on software control, we can control these digital outputs to sync current from the given signal line to a common line. 

The board itself involves essentially 32 repeated circuits where each one consists of a relay and the corresponding circuitry needed to drive that relay. So if you kind of zoom in here, you'll see the same circuit element repeated a bunch of times on the board. And for each relay there's essentially the relay itself. The board’s designed so that the footprint, the holes and faces and everything that are laid out for the relay actually have holes for two different primary relay package footprints. So depending on the application, you could use a smaller relay that will be more cost effective or a larger one that would be useful if you needed to carry higher currents through your contacts of the relay. The whole thing is meant to be mounted in a panel where you would have the primary wiring scheme, the primary wiring architecture of the given test system application and so the contacts of the relay are all routed out to terminal blocks. 

So now I'm going to go ahead and just give a simple demonstration of this board in operation to show you how it will function in a test system. And right here, I'm simply running a very basic LabVIEW application that is toggling the digital output channels of the C series module in the compact DAQ chassis to toggle relays. It's doing so by randomly selecting a relay to toggle and toggling them at a random time interval with an average of one second right now. 

You have the ability to control the relays extremely quickly in software and to do so using a platform that integrates really easily into any LabVIEW application, so we can use NI DAQmx powerful hardware configuration ability integrated into LabVIEW to give it all the channels that would drive our relay's names; tangible names to describe their function or control them on a port basis, that's the goal. That was the goal before to have something generic that could be useful in many different automation applications, give high-performance specifications, be cost effective and easy to integrate into test systems.