Lab #4
For this assignment, you are going to A) revisit Blink with your Arduino, B) explore cool input components, C) write to a text LCD panel, and D) make your very own timer BONUS) make your timer sing!.
Include your responses to the bold questions. Include snippets of code that explain what you did. Deliverables are due next Tuesday. Post your lab reports as 'wiki' pages on your GitHub, and post a link to that wiki on Slack under your channel and #Lab4.
For this lab, we'll be using the Adafruit Metro Mini development board as our hardware platform. This board is a derivative of the Arduino UNO R3. As a platform, Arduino comprises both hardware and software. We'll be using the Arduino hardware; for an IDE, you have the option of using the Arduino software on your laptop.
To use your laptop computer for programming the Metro Mini, you will need to download and install the software on your machine:
1. Blinking LEDs with Arduino
Connect the Metro Mini to your computer using the USB cable. Arduino boards typically come preloaded with a version of the Blink program on it. This code lets its LED (connected on pin 13) blink as soon as the USB cable starts powering the board. In this class, we have previously uploaded a different program to the Arduino. (Remember the helloYouSketch from Lab1).
To get set up, we will use the Blink example code to see how to upload code to the Arduino from our computer. The Blink program itself can be found in the Arduino IDE's example code folder under File->Examples->Basics->Blink. Check it out!
a. What line(s) of code do you need to change to make the LED blink (like, at all)?
b. What line(s) of code do you need to change to change the rate of blinking?
c. What circuit element would you want to add to protect the board and external LED?
To compile and upload your code, take the following steps (note that 1, 2 should only have to be done once):
- In the Arduino program, select the board we are using: Tools -> Board -> Arduino/Genuino UNO
- You may also have to select a communications (or COM) port (Tools -> Serial Port). The port should be something like
/dev/cu.SLCA_USBtoUART(on MAC)/dev/ttyUSB0(on Linux), orCOM3(on Windows, could be another number). If they are not showing up, make sure you've installed the SiLabs CP210x drivers. - To compile your code, click on the "checkmark" on the upper far left of the Arduino development window.
- To upload compiled code to the Arduino, click on "right arrow" besides the "checkmark."
- When the code is uploaded, the Arduino should automatically start running your new code.
Now modify the circuit and program so that you can blink an external LED on pin 9. Don't forget about question (c) above! (Also, don't forget to connect power and ground the power and ground rails of your breadboard, respectively!)
Some tips and reminders:
We don't have extra Arduinos, so be careful.
Remember that the USB connection to the Arduino supplies power.
Check that there are no shorts between power and ground before you plug in the USB cable (and apply power).
Unplug power before modifying circuits!
2. Digitally toggle LEDs on and off using the Arduino
With your LED still connected on digital pin 9, hook up a button circuit on digital pin 2 of the Arduino. One side of the pushbutton attaches to digital pin 2 and via a 10k resistor to Vcc. (Vcc is the supply voltage. In this case, it is 5V.). The other side of the pushbutton attaches to ground directly.
Use either the same circuit you used for the previous step or use the alternative design below. The alternate circuit causes the "on" state of the LED to occur when Arduino pin = LOW, not HIGH, as before.
The Arduino pin configured as an input has a 'high input impedance.' This means that it can sense the voltage without affecting the circuit, like a probe.
Use the Button program (File->Examples->Digital->Button) to make your Arduino into a light switch.
a. Which lines do you need to modify to correspond with your button and LED pins?
b. Modify the code or the circuit so that the LED lights only while the button is depressed. Include your code in your lab write-up.
3. Fading LEDs on and off using Arduino What about those "breathing" LEDs on (old) Macs? The fading from bright to dim and back is done using pulse-width modulation (PWM). In essence, the LED is toggled on and off very rapidly, say 1,000 times a second, faster than your eye can follow. The percentage of time the LED is on (the duty) controls the perceived brightness. To control an LED using PWM, you'll have to connect it to one of the pins that support PWM output —-- which are 4, 5, 6, 9, 10, 11, and 12 on the Arduino.
Use the Fading program [File->Examples->Analog->Fading](https://www.arduino.cc/en/Tutorial/Fading) to make your LED fade in and out.
a) Which line(s) of code do you need to modify to correspond with your LED pin?
b) How would you change the rate of fading?
c) (Extra) Since the human eye doesn't see increases in brightness linearly and the diode brightness is also nonlinear with voltage, how could you change the code to make the light appear to fade linearly?
First, it's important for you to understand that analog input ("analog pin 0") on your Arduino board shares pins with digital input. Below is pinout for the Metro Mini. The pins with name A0-A12 are analog pins.
So while a digitalRead or digitalWrite command reads or sends only a logic-level high or low, an analogRead or analogWrite command reads or sends a range of values.[Example: if you want to read analog pin 0—which corresponds to pin A0 on the right side of Arduino, you would call analogRead(A0)]. Note that the analogWrite function has nothing to do with analog pins; it uses the PWM pins.
Set up the LED output and potentiometer input circuits from the following schematic on your breadboard. This setup is much like the LED fade, except now we're using analogRead to control the fade. Have a look at File->Examples->Analog->AnalogInput for the code.
The potentiometer is an instance of a voltage divider circuit, which we discussed in class. As you might recall:
Change the code so that the LED fades and brightens with the analog value of the potentiometer, like a dimmer. (Save this code! We'll be using it again soon...)
a. Post a copy of your new code in your lab write-up.
The FSR changes resistance — in this case when pressure is applied to the FSR. Here's the datasheet. We'll use a voltage divider with a 22kOhm(originally 27kOhm but they are not avalible right now) resistor, using the analog input with the previous potentiometer code.
a. What resistance values do you see from your force sensor?
b. What kind of relationship does the resistance have as a function of the force applied? (e.g., linear?)
c. Can you change the LED fading code values so that you get the full range of output voltages from the LED when using your FSR?
Let's use your LCD screen to display some interesting information! There is a good deal of example code for playing with your LCD in the Arduino Examples:
File->Examples->LiquidCrystal
Let's start with the "Display" program, which just flashes "Hello World!" These LCDs are a custom part, but there's a lot of information at this page, the pinout and dimensions page and the LCD controller page.
a. What voltage level do you need to power your display? b. What voltage level do you need to power the display backlight?
Solder a 16 pin breakaway header to the LCD so you can connect it to your breadboard.
If you haven't soldered before, we're happy to show you how! PLEASE ASK.
Wire up your LCD according to the schematic below. If you didn't have our diagram, you would use the data sheets for the LCD and follow the comments in the "Display" code to figure out how to wire it up.
Be very careful not to connect Pin 1 and Pin 2 on the LCD, as this can destroy your Arduino. Check the connections for a short between power and ground before you plug in power or the USB cable.
See Tutorial for more information. See LCD Library for the various functions you can use.
Try compiling and running the code. If it doesn't work the first time, check your pinouts...
The 10K pot connected to Vo on the LCD adjusts the contrast, so try adjusting that if your LCD won't turn on. The contrast might be so low that you're not able to see it, so make sure you've checked both extremes.
LCD pin 15 and 16 (LED+, LED-) are designed for background lighting. If you feel the whole screen too dark, you may try to connect pin15(LED+) to +3V or +3.3V and pin16(LED-) to ground. Don't connect pin15(LED+) to +5V as it may burn background light!
Do try to set this up before peeking at this diagram.
b. What was one mistake you made when wiring up the display? How did you fix it?
c. What line of code do you need to change to make it flash your name instead of "Hello World"?
Try a few of the other examples in the folder to get a feel for the capabilities of your LCD. There is a list of all the possible functions at the Arduino LiquidCrystal Library.
Incorporate the LCD into your fading LED/potentiometer code so that you can read out the exact analog value that you are reading in on Analog Pin 0. It's your own lowly multimeter!
d. Include a copy of your Lowly Multimeter code in your lab write-up.
Now build a circuit with two FSR sensors (one from your self and one borrowed from a fellow student) to enable a game of thumb wrestling. Use the LCD to indicate who is squeezing their FSR harder!
e. Include a copy of your FSR thumb wrestling code in your lab write-up.
Leave your LCD set up for Part D of the Lab, and leave it set up when you finish Lab, as we'll use the display again next week.
Make a timer that uses any of the input devices to set a time, and then automatically (or manually, if you prefer) begin counting down, displaying the time left. Make your timer show an alert once the time is up with one of the output devices we connected during this lab, or you have available. (Hint: the sample code for Examples->LiquidCrystal->HelloWorld displays the time in seconds since the Arduino was reset...)
Note that for some of you, the time may seem to be decremented by 10 each second (that is, from 670=>660). Why is this? Do you think it's a hardware or software issue? Think about how 100 vs. 99 is written to the screen, and ask an instructor.
a. Make a short video showing how your timer works, and what happens when time is up!
b. Post a link to the completed lab report to the class Slack.
Let's make the Arduino make some noise! We are going to start with the Tone example program:
Examples->Digital->toneMelody
The official Arduino tutorial for this code is here Add a 75 Ohm resistor to limit the current to the speaker when you hook it up on your breadboard. If you would like it a little louder, you can use a lower value resistor, up to a minimum of 5 Ohms.
Wire it to your circuit with the black to ground and the red to Arduino Micro pin 8.
a. How would you change the code to make the song play twice as fast?
Now change the speed back, and replace the melody[] and noteDurations[] arrays with the following:
int melody[] = {
NOTE_D3,NOTE_D3,NOTE_D3,NOTE_G3,NOTE_D4,NOTE_C4,NOTE_B3,NOTE_A3,NOTE_G4,NOTE_D4, \
NOTE_C4,NOTE_B3,NOTE_A3,NOTE_G4,NOTE_D4,NOTE_C4,NOTE_B3,NOTE_C4,NOTE_A3,0};
int noteDurations[] = {
10,10,10,2,2,10,10,10,2,4, \
10,10,10,2,4,10,10,10,2,4};You'll also have to increase the for() loop index max from 8 to 20:
for (int thisNote = 0; thisNote < 20; thisNote++) {b. What song is playing?
How to upload code using your RaspberryPi over command line.
How to upload the code with x11.