Exercise 6 - Potentiometer

In this exercise, we will learn how to use a potentiometer. A potentiometer is variable resistor that comes in a few different sizes and shapes. The most common shape is a three terminal round knob. The resistance of the potentiometer will change when the knob is turned. In the schematic below, one terminal of the potentiometer is connected to 5V and the other is connected to GND. This creates a potential difference in the middle terminal and forms a voltage divider circuit.

x3

x1

1. Connect the terminal 1,2 and 3 of the potentiometer to 34C, 35C and 36C respectively.
2. Connect a jumper wire to 5V and 34A.
3. Connect a jumper wire to A0 and 35A.
4. Connect a jumper wire to GND and 36A.

Write and Upload the Potentiometer Sketch

In order to execute the sketch for this exercise, launch Arduino IDE then

Click File -> New.

A new sketch editing window will appear. Copy the whole block of code below and paste it into the new sketch window, overwriting the empty setup() and loop() that was pre-created. Ensure that the board selected is Arduino Uno and the right COM port is chosen according to “Board Selection” chapter.

int sensorValue;

void setup() {
    pinMode(A0, INPUT);
    pinMode(13, OUTPUT);
}

void loop() {
    sensorValue=analogRead(A0);
    digitalWrite(13, HIGH);
    delay(sensorValue);
    digitalWrite(13, LOW);
    delay(sensorValue);
}

Click Upload, and the Arduino IDE will prompt you to Save sketch folder as. Enter Excercise_6 into the filename field and click save. Once saved, the Arduino IDE will start to compile the sketch. After the compilation is completed, the Arduino IDE will start to upload the compiled sketch into the STEMTera™ Breadboard. During this stage both yellow LEDs on the STEMTera™ Breadboard will start blinking indicating the Arduino IDE is uploading the sketch to the STEMTera™ Breadboard.

Turn the knob on the potentiometer and notice the RED L LED on the STEMTera™ Breadboard blinks corresponding to the knob.

Understanding the Potentiometer Sketch

The first line of the sketch

int sensorValue;

declares an integer variable called sensorValue. This variable will be used to store the value of the voltage read from the middle terminal of the potentiometer.

In the setup() function, PIN A0 is configured as INPUT and PIN13 is configured as OUTPUT.

void setup() {
    pinMode(A0, INPUT);
    pinMode(13, OUTPUT);
}

The STEMTera™ Breadboard has 6 exposed analogue to digital converter (ADC). The ADC is commonly used to convert analogue voltage to digital value. In this example

sensorValue=analogRead(A0);

the analogue voltage of PIN A0 is being read using analogRead() function and stored into the variable sensorValue. The code then proceed to turn PIN 13 HIGH by executing

digitalWrite(13, HIGH);

after that a delay of a digital value (sensorValue) which corresponds to the analogue voltage read, will be executed. This delay demonstrates the blinking period of the LED as the knob of the potentiometer is being turned.

delay(sensorValue);

With the potentiometer’s both left and right terminals connected to 5V and GND respectively, the middle terminal of the potentiometer will have a voltage swing between 5V and 0V when the knob is being turned from one side to the other side. When the voltage of the middle terminal is read by an ADC, the corresponding digital value of the ADC in this case is 0 to 1023, where 0 is 0V and 1023 is 5V. This digital value when is passed to the delay() function, it represents time in a unit of milliseconds. After the delay, PIN 13 is turned LOW followed by a delay with a value of sensorValue again.

When these instructions are executed in a loop, the RED LED on the STEMTera™ Breadboard will turn ON and OFF in a period corresponding to the position of the potentiometer’s knob.

CHALLENGE! Write a sketch to read the potentiometer value and play a pitch relative to the value.