Virtual Dial

Virtual Dial

Potentiometer

• In this example we will use the potentiometer, a component that allows us to regulate the voltage level that can be read on an analog input pin.

• It has three terminals: one for the power input (5V or 3.3V), another for ground (GND) and the last one for the output voltage.

• It works as a voltage divider: the output will give a voltage value depending on the position of the dial (the closer to the power pin, the higher the value).

Connection and reading

• To connect it to the board you will need to use one of the analog pins.

• It must be connected following the same color scheme, i.e. red with red, black with black, etc.

  

• Once connected, we can find out its value using the read analog pin _ block from Pins category, while specifying the pin number where we have connected it.

For boards like the micro:bit or the micro:STEAMaker we will have to connect with alligator clips or with an adapter for pin connections. For boards with 4-pin connectors there are adapter cables for pin connections.

Challenge 1: Make a small program that displays the value read from the potentiometer

Turtle Library

• In addition to the numerical value, we will try to represent the movement of the potentiometer on the screen with a "virtual dial".

• For this we will use the Turtle library in Graphics and Displays folder, which allows you to draw on the screen in a way similar to the language LOGO and of course, as in Scratch or Snap!).

Draw a line

• To be able to draw a line, the following blocks should be used:
• home to start from the center of the screen.
• set pen color to _ to select a color (default is green).
• pen down to down the pen.
• point in direction _ to point in the desired direction before drawing the line. (home includes points in direction 0).
• move _ to move an amount of pixels in current direction.

Challenge 2: Find the formula to go from the analog input value range (0-1023) to the direction range (0-360º)

• Once we have the formula we can use it to vary the direction of the line according to the position of the potentiometer reading.

• The blocks for fixing the pencil color and lowering it do not need to be inside the loop, they only need to be executed once before starting to draw.

• We will take advantage of the code we had previously to display the value per screen and move the dial at the same time.