Connecting multiple Arduino

I wish to connect multiple arduino units attached to 50 or solar arrays. What would be the best approach to communicate between these units without wireless or ethernet.

i wish to attach all the units to a central connection where data will be collected then sent out via internet.


What is the average / maximum distance between two arduinos?

How frequently and how fast do your boards need to communicate?

The communication is slow , i am thinking updates every 1 to 5 mins roughly.

I was thinking RS-485?

Distance between each unit is roughly 20m

Yes, RS-485 would have been my suggestion. Plenty fast, units can be added and removed, relatively insensitive to ground loops. Topology allows daisy-chaining..

There are some established Arduino network things as I recall.. I'll look..

If you are having 50 'transmitters', or 'slaves', you might want to consider making some cards up - minimal design: atmega, crystal, 2 22 pf caps, 2 0.1uF (100nF) caps, RS485 transceiver, connector for your cable.

Or plop a promini onto a perfboard with the driver and connector. Whole thing in a little weather tight box.

Where is power from? Tapped off the array somehow?

perfect thanks for the suggestions,

The power will be coming from a supply to the trackers to run the motors and such for tracking, just going to have to regulate some voltages thats all.

For this project as well, im just calling the units say every 1-5 minutes for an update, will half-duplex be alright?

So the slaves will just be listening, and then responding when queried?

"Hey #43, send me your data." "#43, Right, here it is."

"Hey #12, send me your data." "#12, Right, here it is."

That would be fine. Save you some wires too.

just wondering, using Rs-485.

On the arduino board i usually monitor through serial with the mini USB.

If i have everything communicating with Rs-485 i will not be able to monitor with the mini usb correct?

Possibly , NewSoftSerial? or is their a RS485 multiple serial arduino sheild, they have one for RS232,

This was mentioned on the blog today:

May well not be a fit for your scenario, but thought it worth mentioning.

Sure, use NewSoftSerial for 2nd serial port. You could make up a multiplexer board also, set of analog switches to switch the RS485 around to the different boards. Or wire it up like a network, see Figure 9 here:

Read the whole page, pick your parts properly.

Thanks for everything I shall let you know know how the project comes along


When considering using repeaters,

if i use say something like this :

for RS-485 communication.

If i were to add a repeater to allow more slaves, would i simply just add another one of these units between a line to boost the signal?

I'm not sure what i need for a repeater.

I have multiple slaves communicating with a master at the moment using my own code and

the mini boards are connected in parrallel through the TX+ and TX- terminal

when i remove power from one slave, all communication from slaves stop.

i fell like this shouldn't be.

any ideas?

nvm, i fixed was on the code side...master was not incrementing slave addresses properly.