Reddit reviews LANDZO 8 Channel 5V DC Relay Module Expansion Board for Arduino Raspberry Pi DSP AVR PIC ARM

You have a lot of choices.

Ultimately it looks like you want to use physical relays (most allow signals up to 250V). You could either use a dedicated multiplexing board (The board is wired such that only one path is connected at a time), or you could use a bank of relays and wire them so that all their common outputs are tied together, and then you just write code that only allows for one connection at a time.

What's most important to you, Cost or Hardware quality?

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If cost is important, go for an arduino + relay board, like this...

https://www.amazon.com/LANDZO-8-Channel-Relay-Module-Arduino/dp/B01NBUDHPB/ref=sr_1_1?ie=UTF8&qid=1500396954&sr=8-1-spons&keywords=arduino+relay&psc=1

The cheapest thing to control it would be something like an arduino microcontroller:

https://www.amazon.com/Arduino-Uno-R3-Microcontroller-A000066/dp/B008GRTSV6/ref=sr_1_3?ie=UTF8&qid=1500397057&sr=8-3&keywords=arduino+uno

You would write you code in LV, which would use a serial message to control the arduino. The arduino has digital outputs that would drive the relay board.

The code on this is not terribly complicated, but you would not be using DAQ drivers, but the VISA serial messaging and you would have to deal with a USB com port on the PC. This adds a little complexity and possible failure mode. This is what I would use in my own home for an inexpensive, non-critical application. You can even get cheaper controllers and relays, but we're talking $40 here.

Another advantage of the arduino is that you could put a fairly simple protection circuit into the controller code, so that if something goes wrong at the PC level or you generate a bug that the relays can shut down or be more sure that they won't short circuit two paths.

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To go the other route, where money is no object (or you need a very robust, mission critical system) and want overly simple programming, you could go with an NI relay board on a PXI chassis. That's going to run in the thousands of bucks, but if I was shipping this off to China on a test rig that I never wanted to have to fix, that's what I would use.



In a local environment where I could easily support a problem (and a problem wouldn't cost us $50K a day), for an employer that would want a compromise between cost and my time, I would probably use an NI-USB 9174 chassis + 2 9482 relay modules. This will run about $1200, but is reasonably robust and very simple to program and is practically plug-and-play in terms of hardware. Remember that to a reasonably sized employer, you cost about $100/hr considering benefits and such. So if you can save 4-8 hours of learning/programming/debugging/wiring/soldering, it's a wash.

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Lastly, I recently saw an Industrial Arduino, which is a relatively inexpensive way to get the cost down but beef up the hardware, for about $200. With one of those, I would not use that cheap relay board, but probably find a set of DIN mount discreet, industrial relays, about $20-50 each.

If this was the solution, I would spend some time to figure out how to talk to the arduino over some other method of communication, other than USB. It's been my experience that USB can be a source of pain in the ass-ness. Driver updates can break things, plugging something else in can break things, hubs can cause headaches, even certain brands of PC come with shit USB controllers that refuse to play nice once in a while.

IF you do use PC + USB in a production environment (which I have done, many times), I suggest buying a dedicated PCI/PCIe USB controller (and get a couple replacements), so that you are not at the mercy of shitty motherboard design or having to deal with driver changes if IT tells you you have to change out the PC.

(OK, I'm getting ahead of myself here)



Note: For all of these solutions, even the serial programming is simple, so it's really about how stable/robust the hardware is. With the arduino, you are relying on relatively inexpensive non-industrial boards that have a relatively high failure rate, along with a bit of your own wiring and a separate code base on the controller. That's not necessarily bad, but I wouldn't send that up on a satellite- and I have actually programmed QA for satellite parts- that's when you spend $10K to get a bank of relays that you don't have to worry about.

Switched PDU's are ideal for this but are quite expensive.

I bought a Raspberry Pi and an 8 channel relay to control the power and reset buttons on my rigs remotely. I just SSH into the Pi remotely to reset a rig manually if needed. Around $50 all in.

It's only really in use when I go home for breaks, if I get more plants I'd buy more sensors and pumps probably and get one of these relay shields or buy a bunch of solenoid valves or something