Arduino relay board distance limitations

I would suggest that you dont try to consolidate all the actual physical control points at the house but instead keep the switches / Reslays at the point of control. Upgrade them for sure to use Arduino, ESP8266 or other modules more suited to automated and modern control systems

Have a House placed master controller for sure, running on a Raspberry PI 2 with 7" LCD would be awsome

The control points though especially given 900M dstance would be better communicated with using either CAT3 or 5 twisted pair ethernet or RS485 serial communications, both of which are good for this distance (There up to 1200M or more)

even WIFI is only typically good for about 300M with no obstructions though a sub Ghz radio link may easily cover the distance, for instance the TI sub GHz radio modules or many other types you can find arround the EBays and AlliExpresses of the world

If you can provide a sketch of you proposed control system, (A Map of the farm so to speak) showing distances and the types of things your controlling, then I will be in a much better position to help

My first question is the operating distance a relay module can safely operate over 22 ga twisted pair wire

The answer to that depends on the current required to operate the relay coil.

Obviously the more powerful the relay, the larger the coil.

You could trigger an optocoupler, which then operates the relay on the board.

It seems you can provide power to the board, but the control wire size is limited.

To give an idea, I have some trip systems at the skifield that are 1km away from the switch.

Bascally 5v is fed into Pin1 (Anode) of an optocoupler, and Pin 2 (Cathode) travels 1km up the wire, then the switch shorts this to the ground wire, which is also at the original source point (effectively a 2km round trip) using telephone cable.

Mark

Thanks Mark! That is exactly what I was looking for. My intention was to use an 8 channel optocoupler relay board, so the relays themselves can be powered remotely. If you are currently running 2km of wire, mine should be fine as well.

01221

There are some things to watch for on commercial opto relay boards.

They are really designed for 12v trigger, and some may not function using 5v switching.

It is relatively simple to either bridge the on board LED (not the best) or add a lower value resistor across the series resistor (usually a 1k).

Terry King has the details on his site.

Opto-Isolated 8 Channel Relay Board(Price reduced again)

BTW the varistor is across the switch contact to prevent lightning from causing any issues if the switch is open.

During the off season we tend to unplug the board, but you might want to consider lightning as it can cause one 'ground' to rise above another 'ground'.

Mark

Hi

I wouldn't opt for either  of these two methods although they may work when you running fairly long distances  I would personally  consider  using RS485  as the protocol to communicate btw smaller devices and processors  a cheaper method  more reliable method of doing this

If you were considering wireless communications you would be far better with physical hardware connections  Its far more reliable than esp8266 at present although this implements a full tcp ip stack you have to consider that you would be using UDP over cat 5  which is the useless datagram protocol as some correctly  describe this as Restful services with json integrating serial port applications using client server technology via web page interface  might be another option but agin unless you've spent some time with this It is unfortunately a question of time  with very in depth theory required

A much stronger alternative is often described as the DCI Bus

The idea of using an op-to coupler is  good design but id apply this to  each receiver  on the output side which sits on your multi-point Rs485 design to drive your relays rather than your input side

That way you can have each microchip addressable

Ideally my suggestion would be to use a master and slave routine on this with the master controller sending out your serial packets which contain destination address op code and CRC checksum with an ack once your relay has been activated 

Hence you then also  have some form of fault diagnosis  in other words has the relay been actuated via ack

Here is some more info on rs485  with schematics for you to study and implement in your design  https://www.dcisite.be/dcibus.html

When producing your final relay driver board and micro receiver on each be very careful about track spacing and also induced RF via the relay coil Ive found this to be quite a problem on previous designs so good decoupling is needed as well as reverse emf protection to prevent destruction of relay driver stage and also upsetting the ports of the cpu

Thats the best advice I can provide based on practical designs that Ive produced myself

For further reading on the RS485 interface please see the following

RS485, specifications and in depth tutorial

I wish you luck with your project

Mark Harrington