Raspberry ADC
As a microcontroller, Pico's chip is composed of thousands of transistors like other microcontrollers. These transistors can only switch between two states: on (1) or off (0) — just like a digital signal, which enables Pico to process digital signals directly. For the analog signals which cannot be described with 0s and 1s, the analog signals must be converted into digital signals before they can be recognized by Pico. The electronic component for this operation is called “ADC (Analog to Digital Converter)". On Pico, there are three ADC channels that can be used. They are located on GP26, GP27 and GP28. When you plug Pico into the Shield, these pins are then connected to the A0, A1 and A2 of the Shield. So when we use sensors that need to utilise the ADC channel to return analog signals, we can only plug them into the A0, A1 or A2 ports of the Shield.