Max wireless relays

We have a potential project on a farm where we need to remotely switch 21 pumps as part of an energy management strategy. The pumps are distanced on average approx 1.5 miles from the center.

I have been looking at the MirX and MirC wireless relays, but would like to know what the maximum amount of wireless relays can be run together. We have the option to either switch each pump individually according to certain conditions, or have them all switch at once.

Any advice will be appreciated.



So the application is one central location controlling pumps at 21 remote locations using contact closures correct?

To get an idea of how many broadcasts the system would be transmitting, how often would the system need to control a pump?

For the maximum of 1.5 miles are there other pump locations between it and the center? It would be preferable to have a wireless go-between at that distance to re-broadcast the signal if there’s an issue such as heavy equipment blocking line of sight.

Thanks for the response.

It is fairly scattered, which might mean some of the signals are between others. We suspect that the pumps will need to be switched 2-3 times per day. I still need to go to site to have a look at the terrain, but what I can see there is no real obstruction except for some trees and a few small hills. But need to confirm.

Here is a Google earth image of the layout. Not sure yet where the main plc will be, so indicated on picture is an assumption. The yellow arc has a 1.8mile radius from my assumed plc location

I didn’t realise it, but there is another farm adjacent to this one which also need similar control. Some of the pumps overlap. Farm1 is marked in yellow and Farm2 in Blue.

Hope this gives a better picture of what the needs are.


Hi Jonathan,

What is the control at the central location? What is the device telling the remote pumps to turn on? Are they contact closure signals, is it software on a computer, a PLC, etc?

Hi Travis. We have a PLC at the central point. Basically, what it is doing is during a power failure when the diesel generator kicks in, it will make use of DI/O to open the contacts. Its to ensure that the generator is not being overloaded. So basically we just want to dump the loads. But would be great to individually control each relay to have a more managed approach.

We can also make use of modbus rtu/tcp over wireless, if you have a solution like that?


Hi Jonathan,

If your PLC can output dry contact closure signals which should control the remote 24 devices then honestly 24 of our MirCR1x products here would be the best solution we can offer at this time:

This is not ideal because you would have 24 1 channel transmitters at the PLC location. Previously we offered MirM which consisted of a single transmitter and multiple receivers but the wireless modules used in that product were discontinued. We plan to release a replacement for MirM one day but it is not currently in development.

Thank you,
Travis Elliott

Ok thanks Travis. Do you think there will be an issue with the other farm, with the overlapping points, as that farm will also need 24x MirCR1x’s? Worried about interference between the two systems.

And your thoughts on range? Boosting the signal or have a high gain antenna installed on units that might require them?


Hi Jonathan,

I do not foresee any interference issues between the two farms but I do worry a bit about network congestion. It might be a good idea for us to isolate the two systems from each other so there is not so much data flowing on the same frequency. If you decide to go with this system we will alter the settings in the units to alleviate that as a possible issue.

I think you will be OK on range but it would be a good idea to order one pair of units and place them in the worst case scenario as far as range is concerned. We do not carry high gain antennas for these products but high gain 900mhz antennas are extremely common and can be sourced from 3rd party suppliers.

I have a set of MirX1’s. Can I use this for range testing?

Absolutely. As long as they have the XBee Pro S3B modules installed in them they will function exactly the same as the MirC boards.

Hi Travis,

I went to the site to do some range testing. Unfortunately we lost signal within the first few 100m. Since its a citrus farm I assume the trees would influence the signal. Have tried a high gain antenna on the transmitter side and we could only get under one mile line of site. Some of the other points are also in small valleys etc.

I see the Xbee S3B has mesh capabilities. Could this resolve the problem?


Yes, I have seen users in the past install this simple modem between Mirror products to act as a repeater. You just need to power it up using a 120VAC to USB power supply: