dear Mr.jerry,

we are happy to help you!!

regarding the external ADC, my experience tells me that its always better to have an external ADC because a uC with an inbuilt ADC (called microconverter)will suffer from noise created by its own crystal, digital ports.

+/- 20mV is a very small signal and can be easily distorted by digital noise. maybe for someother application, it would be convenient to use an inbuilt ADC, but not for this application.

kodi