DTMF MT8870 with arduino for robot

Hi, I have attached my arduino to a MT8870 like in the following diagram: http://www.pablin.com.ar/electron/circuito/telefon/decdtmf/circuito.gif

Problem is that only one column of keys seems to work. This column changes from phone to phone- I have tested this with 2 phones. I have not installed any pull up/pull down resistors and nor is there any buffering b/w the outputs of the MT8870 and arduino, i.e. they are connected directly. Any plausible reason why this is not working? Thanks

code? actual schematic in use?

-j

You should have resisters because the outputs go tri-state when no signal is present, I'd use the internal pullup ones. Buffers should not be required.

What have you got StD connected to? And post your code.


Rob