When you have 20 on the line you have to always wait while the line is busy so you don’t transmit when someone else is already transmitting.

Also for this thing it may be better to use something called a CAN network.It works with a 2 wire twisted pair cable and goes up to 1Mbit and up to 300m.(So if you renovate your house remember to put a twisted pair cable over the whole house and do some really cool house automatisation)

This problem happens to me when I try to power both arduinos from usb at the same time. To avoid this, I usually only use usb on one, the master, and the other i am running off of a separate power supply with no connection to the computer.

I’ve set up a I2C with 2 arduino. Seems to be OK, messages are received but they are read with strange characters. Instead of reeiving ‘hello ‘ i receive 6 characters looking like a quare. my grounds are connected each other diretly.

Any idea where the pb comes from ?

once this will be solve, if I have 20 arduino sending messages all together, will there be any trouble to get them ALL on the master receiver ?

Thanks

Seb

You are allowed, i believe, up to 255 devices connected on the i2c bus. As you can see in the code above, it’s as simple as just giving it a number in arduino, with the master being 0 or undefined.

Check out this forum post, it touches briefly on addressing, http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1221415715/6 If that doesn’t help you, try searching the arduino forums via google or their built in search.

Most of my information came from the forums to begin with.

Hope that helps.

the i2c bus is just two wires, called SCL and SDA. SCL is the clock line. It is used to synchronize all data transfers over the I2C bus. SDA is the data line. The SCL & SDA lines are connected to all devices on the I2C bus. There needs to be a third wire which is just the ground or 0 volts. There may also be a 5volt wire is power is being distributed to the devices. Both SCL and SDA lines are “open drain” drivers. What this means is that the chip can drive its output low, but it cannot drive it high. For the line to be able to go high you must provide pull-up resistors to the 5v supply. There should be a resistor from the SCL line to the 5v line and another from the SDA line to the 5v line. You only need one set of pull-up resistors for the whole I2C bus, not for each device.

Also, I used 1.5k resistors, but any resistor should work from 1k up.

Hope that helps.

I have read in several places that you can enable the internal pullup resistors on the atmega, but it failed miserably for me each time i tried.. i could never establish clear communication.. it was intermittent at best.

Hope that helps, thanks for the kind comment.