Arduino relay board distance limitations

Question

I'm completely new to Arduino, but diving in head first. I presently have multiple isolated control boxes of timers and relays controlling a number of things around my home and hobby farm such as outdoor lighting at dusk, automatic feeding of horses 4 times a day, exhaust fans, opening and closing windows in the barn depending on temp and humidity. Well I think it's time I consolidated all these isolated devices into one controller and get with the times...... My first question is the operating distance a relay module can safely operate over 22 ga twisted pair wire. As I am bringing everything back to a central point in my home, my analog experience tells me to calculate voltage drop. I can remotely power each relay board, but the high/low digital signal is where I get lost. I don't know the current, and not sure if it's even relative with a digital signal. So...... I would appreciate any knowledge you can share with me regarding the maximum distance over 22ga twisted pair you can safely operate a relay module. I have one location of a pump, that is 900m away, will it work???? Can this be compared to DSL internet where the modem can be 7 or 8 km's from the exchange equipment and the digital signal is fine????

Love to hear your comments on this and any experience you've had.

mcb1 · Answer

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

Former Member · Answer

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

Arduino relay board distance limitations

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