Serial.begin ( ); Serial.println( ); analogread ( ); map ( );

Transcription

1 Control and Serial.begin ( ); Serial.println( ); analogread ( ); map ( ); A system output can be changed through the use of knobs, motion, or environmental conditions. Many electronic systems in our world are controlled using variable resistors. Volume controls, light dimmers, and speed control knobs found in many circuits in our homes, work and school use potentiometers to vary resistance. These automated systems are triggered by things such as light (light sensitive street lights), motion (motion triggered paper towel dispensers), or temperature (heaters or air conditioning) which are also varying resistors. Actions happen after a threshold has been reached on input levels. If the light measured drops below a certain level, a street light turns on. If the infrared levels increase below a paper towel dispenser, a motor turns a roll of paper towels. This activity will introduce how variable resistors (a potentiometer knob) controls voltage read by the microcontroller and how it controls the output of lights. In later activities, you will use different variable resistors such as light and temperature sensors to control the output of other actuators such as motors and sound speakers. 44

2 Digital vs. Analog Digital pins have two states: LOW or HIGH, which means the components you use, such as LEDs and buttons can only be ON (low) or OFF (high) ver, e w o H Many things in life are not just on or off, like temperature and sound. Sometimes we need a range of values between HIGH and LOW. For these situations, we use the analog pins. Low High off on 0 volts 5 volts The analog pins translate input voltage into a number from 0 to volts to volts 45

3 Potentiometer Puh-ten-she-om-i-ter A potentiometer, often called a pot, is a variable, or adjustable, resistor. When the knob is turned one way there will be 0 volts sent to the pin connected to the center post of the potentiometer. When it is turned all the way in the other direction there will be 5 volts sent to the pin. The outside prong connects to 5 volts which sends power to the potentiometer. The center prong sends power to the component. The voltage output varies from 0 to 5 volts, depending on the position of the knob. Using analogread () this voltage value, will be read by the microcontroller board as an analog value between 0 and 1023 that is proportional to the voltage coming from the pin. The other outside prong connects to ground. 46

4 Materials needed to wire a potentiometer and one LED. Pot Block Odyssey Board 2 dowels Socket block Potentiometer block 1 F/F wire 1 F/F resistor wire LED Wire clip (optional) Set up the Odyssey Board, dowel, and socket block. (Wire clip is optional.) Your blocks may use any horizontal or vertical dowel holes. They do not have to look exactly like the ones shown. 47

5 Predict what you think will happen when you hook up a potentiometer to a LED? Connect the LED to ground and Digital pin 8 on the UNO. Connect the potentiometer to Analog pin A0. a. Connect the yellow wire to S (signal). b. Connect the red wire to V (5 volts). c. Connect the blue wire to G (Ground). Analog pin A0 You can paste the code or type the code into the IDE to use the pot. It is good practice to type the code in yourself. The following instructions will guide you through the process. a. In the declarations, there will be three things you need to name. The potentiometer, led, and a variable to hold the value coming from the pot. Although you can choose your own names, to make the code easier to understand, we will name the pot potpin, the led ledpin and the variable for the pot value analoginputvalue. b. We will use pin 8 for the led and pin A0 for the pot. c. Go on to the next page for the code. 48

6 Type in the declarations: Only type what is inside the boxed area. You can write your own comments or use the ones below. int potpin = 0; // This names the analog pin that will read the varying voltage signal from the potentiometer. int ledpin = 8; // This names the pin where the signal will be sent to the led. int analoginputvalue = 0; // This names a placeholder for the value that will be read from the potentiometer. Type in the setup: All we need to set up is the led. void setup ( ) { pinmode (ledpin, OUTPUT); // sets pin 8 as an output. Type in the loop: We need to have the UNO read the value from the pot to know the voltage value to send to the led. void loop ( ) { analoginputvalue = analogread (potpin); // This reads the value returned from the potentiometer. digitalwrite (ledpin, HIGH); //Turns the LED on. delay (analoginputvalue); // Leaves the LED on for the input s value from the pot in milliseconds. digitalwrite (ledpin, LOW); //Turns the LED off. delay (analoginputvalue); // Leaves the LED off for the input s value from the pot in milliseconds. Upload the sketch. You should see the LED blink faster and slower as you turn the potentiometer knob. As the value from the pot is closer to 0 the LED delay will be shorter causing the light to blink more rapidly. As the value is closer to 1023 the delay will be longer, causing the light to blink more slowly. 49

7 Using the Serial Monitor The serial monitor allows your computer and Arduino to communicate data to each other. You can use the serial monitor to see the potentiometer in action. 1. Open the Serial Monitor: Under the Tools menu on the IDE click Serial Monitor Or Click the magnifying glass in the upper right corner. 3. Add this coding statement on the next page to your sketch. 4. Upload the new sketch and open the serial monitor. Turn the potentiometer slowly as you watch the Serial Monitor on your computer. 50

8 These two lines of code will allow us to actually see the values being read by the Potentiometer in real time using the serial monitor. Add the two statements marked in red to your sketch. The line below is added to the setup function to open the serial communication port between the UNO and computer. void setup ( ) { pinmode (ledpin, OUTPUT); // sets pin 8 as an output. Serial.begin (9600); // opens the serial port at 9600 bps. The line below will print the potentiometer value in the serial monitor on the computer. void loop ( ) { analoginputvalue = analogread (potpin); // This reads the value returned from the potentiometer. Serial.println(analogInputValue); // This will print the value of the returning signal. digitalwrite (ledpin, HIGH); //Turns the LED on. delay (analoginputvalue); // Leaves the LED on for the input s value from the pot in milliseconds. digitalwrite (ledpin, LOW); //Turns the LED off. delay (analoginputvalue); // Leaves the LED off for the input s value from the pot in milliseconds. Upload the sketch and open the serial monitor. Watch the monitor as you turn the potentiometer knob. 51

9 Understanding the Arduino map function. map ( ) Mapping is a function for the arduino that maps between two scales with different ranges. It takes an analog input range and remaps, or re-assigns the high and low values to a proportional output range between corresponding high and low values. This is great for tying sensor or human input to actuator output Value read by the pot or other sensor from pins A0-A Value mapped to the digital output The input sensor values may not always range from exactly and the output value needed may not be exactly The code syntax for the map function needs 5 parameters: map(value, fromlow, fromhigh, tolow, tohigh); map(,,,, ); Variable to be manipulated Lowest value you observe or expect the input variable to be. Highest value you observe or expect the input variable to be. Lowest output value needed. Highest output value needed. 52

10 To vary the brightness of the LED rather than the blink rate, we will map the values coming in from the potentiometer on a scale of and translate the values to a scale of Here is the line of code calling the map function: int brightness = map(potpin, 0, 1023, 0, 255); //maps the light values to a pitch This line assign the int brightness, the value that is mapped from the incoming analog signal ranging from to the digital output on a scale from Run the following code with the same circuits used for the prior example and see what happens to the brightness of the LED when the potentiometer is turned. int potpin = 0; //this is the analog pin that will read the varying signal coming from the potentiometer int ledpin = 8; // this is the pin that will send signal int analoginputvalue = 0; // this is the number being read from the potentiometer (0-1023) void setup() { pinmode(ledpin, OUTPUT); // sets pin 8 as your output Serial.begin(9600); void loop() { analoginputvalue = analogread(potpin); // reads the value coming from the potentiometer int brightness = map(analoginputvalue, 0, 1023, 0, 255); //variable that maps the light values to range analogwrite(ledpin, brightness); //Sends the mapped signal to the ledpin based on the analog value from the pot 53