Can someone please help me with the multimeter's working please? I wish to measure an AC voltage using it and dynamically send the reading as an input to a micro-controller which does further processing. The problem with this is that the grounds of the multimeter and the micro-controller are different.Can anyone suggest me a way of proceeding further?

Hi Steve,
Indeed, it is a digital multimeter. the outputs from the ICL710x chip that go into the seven segment display are being used to kind of decode what the reading being displayed is.These outputs are square waves of high value 9 volts and low value 4 volts with respect to the battery negative. These are either in phase with the clock pulse of the multimeter or out of phase with them. Being out of phase of a particular output leads to the corresponding segment lighting up. So we need to feed the XORs of each of these outputs with the clock pulse to the micro-controller where further code decodes what the voltage being measured is. We are supposed to measure the terminal voltage of a Self Excited Induction Generator. It is a feedback circuit where the feedback is determined by the micro-controller.
Connecting the negative of the battery to the ground of the micro-controller was not a problem when DC voltages were being measured. But with AC voltage, the multimeter blows up as soon as one measuring terminal is connected to one of the generator terminals. Not sure what the reason is...
I hope I could clarify the problem to you somewhat.
Please help.
Regards.