analog_in

Analog Input Example

In this example we will see how to read the analog value of a pin. This means reading a value between 0 and 1023 that tells the voltage applied to the pin. 0 means 0 volts 1023 means 3.3 volts.

Wiring Diagram

We start from the same circuit as the Digital Out example, and we add a potentiometer. The center pin of the potentiometer is connected to pin 1 of the micro:bit the other two pins are respectively connected to GND and 3V.

Extra hardware:

• A breadboard
• An LED
• A 47k ohm resistor
• A potentiometer

Wiring:

Code

To read the analog value of the IO pin we are going to use the function Analog of the package MicroBit.IOs.

   function Analog (Pin : Pin_Id) return Analog_Value
     with Pre => Supports (Pin, Analog);
   --  Read the voltagle applied to the pin. 0 means 0V 1023 means 3.3V

Arguments:

• Pin : The id of the pin that we want read the analog value

Precondition:

The function Analog has a precondition that the pin must support analog IO.

In the code, we are going to write an infinite loop that reads the value of pin 1, and set pin 0 to the same value.

This means that you can control the brightness of the LED using the potentiometer.

Here is the code:

with MicroBit.IOs;

procedure Main is

   Value : MicroBit.IOs.Analog_Value;
begin

   --  Loop forever
   loop

      --  Read analog value of pin
      Value := MicroBit.IOs.Analog (1);

      --  Write analog value of pin 0
      MicroBit.IOs.Write (0, Value);
   end loop;
end Main;