Arduino 6: Analog I/O part 1. Jeffrey A. Meunier University of Connecticut

Transcription

1 Arduino 6: Analog I/O part 1 Jeffrey A. Meunier jeffm@engr.uconn.edu University of Connecticut

2 About: How to use this document I designed this tutorial to be tall and narrow so that you can read it on one side of your screen while you follow along in the rest of the display area, like this: Tutorial work area Also, the pages in this tutorial are designed to be viewed as whole-page slides. I describe how to do that next. 2

3 Set your PDF viewer to single page mode (Mac) On a Mac, a PDF file will open in the Preview application by default. Hide the side bar and set it to Single Page. 3

4 Set your PDF viewer to single page mode (Windows) In Windows, a PDF file will open in the Reader application by default. You can open the menu from the icon in the upper left corner of the window and then choose Split Left or Split Right depending on your preference. Then right-click on the document and choose the One page viewing option. 4

5 Install Acrobat or some other reader (Windows 10) It seems that Microsoft has disabled (or will soon disable) the Reader application in Windows 10. You will need to use some other PDF application. You can install Adobe Acrobat Reader or just use a web browser to view PDF files. Whatever reader you use, I recommend setting it to page-mode in order to make it much easier to use. 5

6 Introduction This exercise in the series of exploring the I/O (input & output) capabilities of the Arduino will have you use its analog I/O features. 6

7 Objectives The objectives of this tutorial are: Understand how analog differs from digital. Use some of the analog input components that come with the Arduino kit to build an analog sensing circuit. Write a program that interacts with the circuit. 7

8 Prerequisites Before proceeding with this tutorial: Be sure to download the latest version of the arduino.py module found here: rduino/support/index.html I have added some features to it that you will need to use in this exercise. 8

9 Outline These are the sections you'll go through in this exercise: 1. Background 2. Potentiometer circuit 3. Potentiometer program 4. LED dimmer circuit 5. LED dimmer program 9

10 1. Background New arduino functions The arduino.py module has been improved to make it much easier to use. This is how you have been writing Arduino programs in Python: import arduino a = arduino.arduino() a.serialconnect() a.pinmode(13, 'o') a.digitalwrite(13, 1) a.serialdisconnect() That program will still work fine, but you can do it a little differently if you prefer. Keep reading. 10

11 1. Background New arduino functions This is an improved version of the same program: import arduino arduino.usbconnect() arduino.pinmode(13, 'o') arduino.digitalwrite(13, 1) arduino.usbdisconnect() Note these changes: The arduino.arduino() function call is gone. The serialconnect function has been renamed usbconnect. The remaining function calls are now called on the arduino module instead of that a variable. 11

12 1. Background New arduino functions That doesn't look like too much of an improvement, but keep reading. The next few slides show you how much better it can get. 12

13 1. Background Importing everything In this tutorial I use a different style of the import statement that looks like this: from arduino import * instead of just this: import arduino If you use the from style of an import, then you don't need to use the module name in front of all the functions in that module. 13

14 1. Background Importing everything Thus, we can change this program: import arduino arduino.usbconnect() arduino.pinmode(13, 'o') arduino.digitalwrite(13, 1) arduino.usbdisconnect() into this program: from arduino import * usbconnect() pinmode(13, 'o') digitalwrite(13, 1) usbdisconnect() Which, to me, is much easier to write and to understand. 14

15 1. Background Analog and digital Recall that a digital value is one that is represented by some (usually) small set of digits. The extreme case is that of a binary value, whereby we use the two digits 0 and 1. An analog value is one that can take on any value within a certain range (even a fractional value). For example, the ambient temperature outside the building you're in is an analog value that ranges from well below freezing in the winter to in the mid-90s F during the summer. 15

16 1. Background Analog and digital Some thermometers show the temperature reading on an analog scale: You can tell it's analog because given any temperature outside, the thermometer will indicate that temperature exactly to the smallest fraction of a degree. 16

17 1. Background Analog and digital A digital thermometer, on the other hand, displays the temperature using digits: It may be just as accurate as an analog thermometer, but there's a problem: the digital thermometer shown above can't resolve (rather, it won't show you) anything less than 1/10 of a degree of accuracy, whereas the analog thermometer can (even though it may be really hard to read). 17

18 1. Background Analog on the Arduino The Arduino has the ability to read an analog value from the real world using any one of a variety of analog sensors. Your kit includes a light sensor, a temperature sensor, and a potentiometer, which is like a volume control knob. The Arduino can also emit an analog signal that varies in the range of 0 to 5 volts, although it's not a true analog value. It actually chops the range 0-5 V into 256 discrete steps, but those steps are small enough that it's hard for us to discern that it's not truly analog. Now let's use these sensors and build some circuits! 18

19 Outline 1. Background 2. Potentiometer circuit 3. Potentiometer program 4. LED dimmer circuit 5. LED dimmer program 19

20 2. Potentiometer circuit Introduction Pronounced po-ten-chi-om-eter. This is one of the most useful analog input devices. It has a knob that you can turn, and the Arduino can read the position of the knob with a high degree of accuracy. You can use a potentiometer for just about anything you can imagine: to vary the delay at which a light blinks, to change the brightness of a light, the volume of a speaker, or many other things that you haven't seen yet with this kit. 20

21 2. Potentiometer circuit Components needed Arduino board USB cable breadboard 3 wires (any color) 3 connecting pins (twist individual ones off the long pin strip) potentiometer (check the front label on the kit box to locate the part) 21

22 2. Potentiometer circuit Build the circuit This is a rather easy circuit to set up. 1. Plug the potentiometer into the breadboard such that each of its pins is in a different numbered row. 2. Plug three pins into the same rows as the potentiometer's pins. 3. Connect three wires to the pins. The middle wire is the one you care the most about. That's the yellow one here: 22

23 2. Potentiometer circuit Connect the wires Red board Find the analog input pins in the lower right corner of the board: 1. Connect the potentiometer's middle wire to the yellow S analog input pin for channel A0. It's the left-most one. They're labeled A0 to A5. 2. Connect one of the other two wires to a G pin (any pin in the blue row). 3. Connect the last wire to a V (any pin in the red row). 23

24 2. Potentiometer circuit Connect the wires Blue board Find the analog input pins in the lower right corner of the board: 1. Connect the potentiometer's middle wire to the to the A0 input pin. It's the left-most pin in the blue row. 2. Connect one of the other two wires to any pin in the black row. 3. Connect the last wire to any pin in the red row. 24

25 Outline 1. Background 2. Potentiometer circuit 3. Potentiometer program 4. LED dimmer circuit 5. LED dimmer program 25

26 3. Potentiometer program Make a new folder Make a new folder for this exercise. Name it Analog IO. Find the arduino.py program that you used in the previous exercise and copy it into this new folder. 26

27 3. Potentiometer program Start IDLE Start IDLE and enter the statements that every Arduino-Python program must start with: 1. Import everything from the arduino module. 2. Open a USB connection. The statements are shown on the next slide if you forgot how to do it. 27

28 3. Potentiometer program Initial program statements from arduino import * usbconnect() Remember that you may need to supply the name of your serial port in the usbconnect statement. 28

29 3. Potentiometer program Display A0 in a loop Add statements to your program so that it does the following things. Start an unbounded while loop. Inside that loop, do these two things: 1. Use the analogread statement to read the value of analog channel Display that value. I show the statements on the next slide. 29

30 3. Potentiometer program Display A0 in a loop An unbounded loop is one that doesn't end. Another name for it is infinite loop. while???: What goes here? # analog read chan 0 # display that value 30

31 3. Potentiometer program Display A0 in a loop An unbounded loop is one that doesn't end. Another name for it is infinite loop. while True: # analog read chan 0 # display that value Solution on next slide 31

32 3. Potentiometer program Display A0 in a loop An unbounded loop is one that doesn't end. Another name for it is infinite loop. while True: a0 = analogread(0) print(a0) 32

33 3. Potentiometer program Display A0 in a loop An unbounded loop is one that doesn't end. Another name for it is infinite loop. while True: a0 = analogread(0) print(a0) There are different ways to write the statements in the loop, but this is my preferred way. I like naming variables in the program based on what Arduino channel they were read from or are being written to, like a0 or d13. 33

34 3. Potentiometer program Run the program Here's the output: The number changes as you twist the potentiometer ^CTraceback (most recent call last):... KeyboardInterrupt >>> 34

35 Outline 1. Background 2. Potentiometer circuit 3. Potentiometer program 4. LED dimmer circuit 5. LED dimmer program 35

36 4. LED Dimmer circuit Components needed In addition to the parts from the previous section, you will need these parts: LED: any color; the kind with 2 pins there's a single multi-color LED with 4 pins, but we're not going to use that one here 220Ω resistor: or a 1K Ω resistor; if you have options then choose the one that has the smaller value 2 wires: any color 2 connecting pins 36

37 4. LED Dimmer circuit Assembly Notice that the LED has two pins, one of which is shorter than the other. The sort pin is referred to as the negative pin, or cathode, and the long pin is the positive pin, or anode. Short = Cathode Long = Anode 37

38 4. LED Dimmer circuit Connect the LED & resistor 1. Plug the LED into two rows of the breadboard, making a note of which rows the long and short pins are in. 2. Plug the resistor into the breadboard so that one of its pins is in the same row as the resistor's negative pin. Its other pin can go into any other row. 3. Connect two pins and wires as shown. Anode wire Long Short Cathode wire 38

39 4. LED Dimmer circuit Connect it to the Arduino Connect the free end of the cathode wire to one of the blue G pins in the top row of pins on the Arduino. Connect the free end of the anode wire to digital output D11: locate D13 in the yellow row of pins, and it's the second one to the right of it. Even though D11 is a digital output pin, the Arduino can do analog output on it. It does that through something called pulse-width modulation, which I don't want to get into right now, but have a look at that link if you want to learn more. 39

40 Outline 1. Background 2. Potentiometer circuit 3. Potentiometer program 4. LED dimmer circuit 5. LED dimmer program 40

41 5. LED dimmer program About analog input & output Analog input: Using an analog input gives you a value in the range 0 to Analog output: The Arduino expects an analog output value to be in the range 0 to 255. You will add to your existing program so that it takes whatever the value it read from analog input A0 was and sends it to analog output D11 (it's an analog output sent over digital pin number 11). The value that it sends to D11 will need to be scaled first so that any number in the range 0 to 1023 becomes a number in the range 0 to

42 5. LED dimmer program Scaling input to output There is a function called converrt in the arduino module that converts a number in one range into a number in another range: convert(value, fromlo, fromhi, tolo, tohi) For example, to convert a temperature in Fahrenheit into a temperature in Centigrade you could use this statement: >>> convert(70, 0, 212, 0, 100) 33 Fahrenheit range Centigrade range 42

43 5. LED dimmer program Scaling input to output In your program you need to convert a number from the range 0 to 1023 into a number in the range 0 to 255. In this case fromlo is 0, fromhi is 1023, tolo is 0, and tohi is 255. If the analog value is in a0, then the call to the map function you need will look like this: d11 = convert(a0, _, _, _, _) Add that statement to your program and fill in the blanks. The statement should go inside the while loop below all the existing statements. 43

44 5. LED dimmer program Write the program Now you need to send the value in d11 to the analog output channel number 11. The statement will look like this: analogwrite(channel, value) Can you complete that statement by supplying the proper things for channel and value? Answer on next slide. 44

45 5. LED dimmer program Write the program Now you need to send the value in d11 to the analog output channel number 11. The statement will look like this: analogwrite(channel, value) Can you complete that statement by supplying the proper things for channel and value? Answer: analogwrite(11, d11) 45

46 5. LED dimmer program Run it Run the program in Python. Turn the knob on the potentiometer. The LED's brightness level should change. w00t 46

47 Outline 1. Background 2. Potentiometer circuit 3. Potentiometer program 4. LED dimmer circuit 5. LED dimmer program You're done! 47