Starts the ADC
Not available on the imp004m or imp005
This method tells the sampler to begin converting analog signals to digital data. It returns immediately: sampling proceeds under interrupt, and the callback passed to sampler.configure() will receive the sampled data buffer by buffer as they are filled.
Sample pin 5 (imp001 or imp002) at 8kHz and A-law compress the data, for four seconds. The buffers will contain 8-bit A-law data. After configuring the sampler, we call hardware.sampler.start() to begin the process.