Interfacing to I2C in PM2525

[cowasaki]

I'm trying to connect to the I2C bus in the PM2525.  I've extended the lead which goes from the main board to the display board so that it goes to a breadboard in the middle and the meter works as it did before.  Now if I connect the SDA  & SCL lines to an Arduino the PM2525 keeps resetting.  I only need to see the I2C data as it goes past and don't need to write to the bus.  What would people use to connect to it?  Diode & pull-up resistor, op-amp buffers, opto-couple, transistor?

[rstofer]

I don't understand how you have the Arduino set up.  If it has an address that matches the display board, it will try to control the SCL and SDA lines as is the PM2525 main board.  If it doesn't have a matching address, why would it listen to the conversation?

I suppose you could do something to get the Arduino I2C into a promiscuous mode but I'm not sure what it is.

If you are only monitoring the signals, like this 'sniffer', then it shouldn't interfere in any way with the conversation.

https://hackaday.com/2011/05/21/arduino-i2c-sniffer/

OTOH, the sniffer just captures edges, decoding is done elsewhere.