Why can't my BJT common emitter trigger the pin interrupt of an MCU?
Do you have a pull-down or pull-up resistor enabled in the MCU? Because I would not expect the voltage to change when you connect it to the MCU, assuming a high-Z input and the same power supply voltage. So if you have that enabled, turn it off. 

Regardless, as others have said, this is a pretty marginal circuit- the bias method is dubious (beta-dependent). If your electret capsule has less sensitivity than the original tinkerer that won't help either.