# Ada for micro:bit Part 5: Analog Output

## by Fabien Chouteau – Oct 13, 2020

Welcome to the Ada for micro:bit series where we look at simple examples to learn how to program the BBC micro:bit with Ada.

If you haven't already, please follow the instructions in Part 1 to setup your development environment.

In this fifth part we will see how to write an analog value to a pin. The micro:bit doesn't have a real digital to analog converter, so the analog signal is actually a Pulse Width Modulation (PWM). This is good enough to control the speed of a motor or the brightness of an LED.

There is a limit of three analog (PWM) signals on the micro:bit, if you try to write an analog value to more than three pins an exception will be raised.

### Wiring Diagram

For this example we use the same circuit as the pin output example.

### Interface

To write an analog value to the IO pin we are going to use the procedure Write of the package MicroBit.IOs.

procedure Write (Pin : Pin_Id; Value : Analog_Value)
with Pre => Supports (Pin, Analog);

Arguments:

• Pin : The id of the pin that we want to read as digital input
• Value : The analog value for the pin, between 0 and 1023

Precondition:

• The procedure Write has a precondition that the pin must support analog IO.

In the code, we are going to write an loop with a value that goes from 0 to 128 and set write this value to pin 0. We could go from 0 to 1023 but since the LED doesn't get brighter after 128, there is no need to go beyond that value.

We also use the procedure Delay_Ms of the package MicroBit.Time to stop the program for a short amount of time.

Here is the full code of the example:

with MicroBit.IOs;
with MicroBit.Time;

procedure Main is
begin

--  Loop forever
loop

--  Loop for value between 0 and 128
for Value in MicroBit.IOs.Analog_Value range 0 .. 128 loop

--  Write the analog value of pin 0
MicroBit.IOs.Write (0, Value);

--  Wait 20 milliseconds
MicroBit.Time.Delay_Ms (20);
end loop;
end loop;
end Main;

Following the instructions of Part 1 you can open this example (Ada_Drivers_Library-master\examples\MicroBit\analog_out\analog_out.gpr), compile and program it on your micro:bit.

See you next week for another Ada project on the micro:bit.

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### About Fabien Chouteau

Fabien joined AdaCore in 2010 after his engineering degree at the EPITA (Paris). He is involved in real-time, embedded and hardware simulation technology. Maker/DIYer in his spare time, his projects include electronics, music and woodworking.