Using same i2c addresses?

Hello,

I have done more research since my last post and realize that in order to use devices with the same i2c address you need to use an i2c multiplexer. In my case, the PN532 RFID shield from adafruit has a built in address of 0x48. If I want to use two I need to have that multiplexer.

My question stems from not understanding i2c completely. What happens if I hook up both shields without the multiplexer? I don't really care which one reads/writes to a tag. Can I just use the same i2c address for multiple RFID readers and use them as if they were just one giant rfid reader? In the end I just want to have a larger area where a tag could be read in.

Thanks for any information beforehand!

What will happen is the the data will get corrupted and you will not read the correct stuff. It is also possible that the slaves will hand and you won’t get anything.
Your other option is to bit bang another pair of pins as an I2C bus or use a softi2C libary to do it for you.

Thanks for the quick reply!

I will try using a multiplexer and see where I get! I have saved the wiring diagram you've posted on another thread about using pull-up resistors on a multiplexer for i2c and will refer to that. Do you have a specific favorite in regards to a i2c multiplexer, or are they a dime-a-dozen?

Thanks again!

Just make sure that it is a bi-directional one for the data at least. That normally means an analogue one.

Here's a nice I2C mux from one of the forum members http://www.dsscircuits.com/index.php/i2c-multiplexer

Thanks for all the help!