Hi, i am trying to communicate 2 mbed, by using the I2C lines with optocoupler. But i did not get any result. I am not sure if its the connection. I found the above picture from the internet, and connected it this way. Is it the right connection? or must i reduce the frequency.

Thank you.

What distance are you trying to communicate over? There may be a simpler way ....

They are connected side by side.

Unless you really need the I2C support, the simplest method, over such a small distance, is to just use the Serial port. Connect the TX on one mbed to the RX on the other and vice-versa. Then use some code like this:

// config serial port for connection to other mbed
Serial mbed1Serial(p13,p14);    // tx, rx
char a = 0;

...

mbedSerial.putc(a);  // send char

...

and then on the other mbed, have it waiting for the character to come though:

// config serial port for connection to other mbed
Serial mbed2Serial(p13,p14);    // tx, rx
char char_rx = 0;

...

char_rx=mbed2Serial.getc();  //get char

...

Or instead of sitting there waiting, it could be set up to respond to the interrupt generated when there is a serial character just received.

To go longer distances (in my case 30m of ethernet cable, in a noisy environment) I have used a MAX3232 chip at either end between the two mbeds and that seems to have worked OK (though I need to do some more testing to be sure).

Hope that helps in some way.

hi, i not sure if i can use serial because i am trying to communicate mbed to another board that only has smbus, and i2c is the closest thing to smbus. But thank you for the reply. i will keep trying.

Sorry, I thought you were trying to connect 2 mbed's together.

the board with the smbus run on high voltage, im afraid that if the board has some problem, the mbed might received high voltage and spoil.

Have a look at:

http://www.eetimes.com/design/embedded/4025023/Opto-electrical-isolation-of-the-I2C-Bus

Hi, have you used the Avago optocoupler ? They are high speed , digital.

You can also have a look on the i2c isolators from Analog Devices:

http://www.analog.com/en/interface/digital-isolators/products/index.html#Isolated_I2C_Isolators

Peter

Hi, i have successfully connected the I2C with the optocoupler. Reason was that i though the SCLK should only be in 1 direction. So now i connected the SDA and SCLK both bi directional. And yes, i am using the Avago optocoupler. Really thank you all for your help.