Simple RJ45 - Cat6 Remote Switch Box Ideas needed

Thread Starter

Vinny7102

Joined Feb 5, 2017
8
Hello Guys,
This is my first post to AAC so I'll try to be descriptive enough here.

I have a project for construction equipment where I have a main PLC box, and 3 remote toggle switch boxes (each located about 75' away from the PLC).
The PLC contains all the programming needed to run various parts of the equipment and the 3 switchboxes each have a variety of 10 simple DC toggle switches (on/off, on/off/on, on/on.ect...) for a total of 18 switch states per remote box.
My PLC has two 32 point input cards for a total of 64 inputs to read the switch states and can read inputs ranging from 3VDC to 24VDC.

Currently I have things set up using a rather large 19pin cable for each switchbox to the PLC box, but this is rather large and at 75', pretty expensive. The nice thing about it is that the action of toggling and reading the switches is practically instant and all is running with 24VDC.

I am posting this to maybe find some ideas on how I can eliminate the large cables and use a single ethernet cable to power the switches and decipher and send the switch states from the switchbox to the PLC. I've seen this technology used in a lot of equipment but not sure what protocol is used to create this network.
I've done some research on Arduino networking, I2C, CAN bus, and others but am quite confused on which would work for my needs. Example, Some say that I2C will only be accurate for short distances and timing is very important for these switches (at least 50ms response time).

Any advice or ideas would be very much appreciated.

Thanks,
Vince
 

panic mode

Joined Oct 10, 2011
1,783
I2C is meant to be used on a PCB so lengths you are interested in are not something i would consider.

simple way to reduce number of conductors is to somehow encode switch states.

one obvious solution is to use filedbus such as DeviceNet and distributed I/O.

another very simple option is to combine switches with resistors and use analog inputs at PLC end. this is particularly convenient when you want things to be simple, robust and easy to service on site by electrician. you get also very fast response time.

if you want to go fancy, you can use wifi too but then - what is your skill or comfort level...?
 

tranzz4md

Joined Apr 10, 2015
310
You've got lots to learn about that stuff, and this AAC site should contribute some. If you work for free, there may be a few things cheaper than 150' of cat 5 wire, but 3 cat5 gives you more than you need to monitor 10 SPST switches.

Just sayin'.
 

Marley

Joined Apr 4, 2016
293
The professional way to do this is using a fieldbus. There are various propriety versions out there. Most of these now communicate over ethernet (Profinet for example) using standard CAT5 cable. It also means you can extend to longer distances using optical fibres. Or even the whole world using the internet! You can probably get an add-on unit for your PLC. This will be quite expensive, however but has many advantages.

If you want to do this on the cheap, I would probably use serial over RS232 or even better RS485. Your PLC may already have a serial port. You would need to make or buy a serial I/O device that would convert your switch states to a code that is sent serially.
 
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