Connect 2 arduino's with wires


I would like to connect 8 arduino's together and I dont know how to do it.

7 of them are thermometers (1 per room in my house) and the last one is the thermostat collecting all temperatures and managing the central heating system.

I dont want to use expensive devices like wireless Xbee, bluetooth or wifi. Is it possible to do it with single wires using the RX-TX pins ?

If yes

  • wich cables and how to connect ?
  • wich arduino library and wich code ?
  • how variables are moving from the code of one device to another ?

If not possible

  • do you have another cheap solution ?

Many thx to all of you

John from Belgium

it might be a bit over kill but some implantation of rs-485 which is for long distance also multiple devices might be good i am using modbus protocol over rs-485 with 4 arduino's

How far apart are the devices, and how fast do you expect to collect results?

Modbus would defnitelly be a good way to go, because I have seen that many commercial thermostats use RS485.

Something which could be adapted to your needs is discussed at...

In that, I discuss connecting an Arduino to another microcontroller (a second Arduino could have been used), via just 3 wires: A ground connection, a serial data line from A to B, and a serial data line from B to A.

Although to strains the usual meanings of the words, the project illustrates perhaps the world's simplest "client / server" set up.

Are you having Arduino control a damper to each room, to control the air flow?

Hello everybody,

Some info about all you answers :

The longest distance from one arduino temperature sensor to the thermostat will be max 30 meters.

Each of them will also control en electronic tap to switch on the radiators.

The speed of transfering data can be very low. To maintain a temperature in a room, it's sufficient to measure every 5 minutes by instance.

Another idea to reduce the cost of connections management (to avoid a real network) is to establish a single connection based onto 2 arduino's (room & thermostat) and to build an electronic switch reading the 8 devices step by step.

Have a nice day


Wireless could be achieved for less than $40 ($80 if you want bi-directional comms)

A suggestion is to use I2C or Two Wire to communicate. You would need three wires going to each arduino. SDA (analog 4), SCL (analog 5), and Ground. You could add power if you wanted.

I am unsure of the maximum limit for the total bus.