CS12020 (Computer Graphics, Vision and Games) Worksheet 1

Transcription

1 CS12020 (Computer Graphics, Vision and Games) Worksheet 1 Jim Finnis (jcf1@aber.ac.uk) 1 Getting to know your shield First, book out your shield. This might take a little time, so be patient. Make sure your name, address and the serial number of the shield have been logged. Your shield is a circuit board which sits on top of your Arduino, connecting to its pins. Pins which the shield doesn t use can still be accessed, by connecting to them on the shield rather than the Arduino they are passed through to connectors on the shield. In fact, you can connect to pins the shield uses as well, but don t it could stop the shield working! The shield itself is shown in Figure 1. Your Arduino, plugged in underneath Digital pin 13 LED y x LED display Buttons 1-5 headers passed though from the Arduino Figure 1: The CGVG shield You should be able to see how your Arduino fits underneath, but don t connect it yet. It has the following parts: An 8x8 LED display. Each pixel has two LEDs, red and green. This means we can show four different colours: black (all off), red, green and yellow (both on). An LED which is connected to digital pin 13, like the LED on the Arduino itself (which will be hidden by the shield). Five push buttons. 1

2 Some connectors called headers in the electronics trade. These are female headers, and they connect directly to the Arduino s pins. With this shield we can write simple games, responding to the buttons. We can also connect the Arduino to other Arduinos to play multiplayer games using serial communications. You ll be provided with a library to help you control the LED and read the buttons with a fairly simple API (Application Programming Interface). 1.1 Connecting your shield Now you can connect your shield to your Arduino. Always do this with the Arduino disconnected from the PC. The connection is shown in Figure 2. Make sure you line everything up correctly the six pins on the right should slot neatly into the headers for the analog pins A0-A5, which should be labelled on your newer Arduinos. The rest should slide into place once you have those lined up. Don t force it ask for help if there s a problem. Figure 2: Connecting your shield Once you re set up, get a demonstrator to look at your shield to check you ve connected it correctly to your Arduino. 1.2 Making sure you can save your programs (if on a public workstation) The Macs in the Orchard and the public Windows workstations both use Documents/Arduino as your sketchbook directory. However, the Linux machines C56 are configured differently. This is easily fixed in the Arduino IDE, open File/Preferences... in the menu and edit the sketchbook directory to be /home/xxx/documents/arduino (where xxx is your user ID). Now quit and restart the IDE. 1.3 Installing the library The AberLED library can be downloaded as a Zip file from cs120.shtml. To install it, open your Arduino IDE and from the menu select Sketch/Import Library.../Add Library... Then select the downloaded file. 2

3 1.4 Running a test Now you are ready to run a test. Connect your Arduino and shield to the PC, and enter the following code into the IDE: #include <AberLED. h> void setup ( ) { AberLED. begin ( ) ; AberLED. c l e a r ( ) ; for ( int i =0; i <8; i ++){ AberLED. s e t ( i, i,yellow) ; AberLED. swap ( ) ; void loop ( ) { You should see a yellow diagonal line on your display. Here s how the code works: #include <AberLED. h> // This i s t h e s e t up f u n c t i o n, which runs once. I t s // t h e only code which runs, because our l o o p ( ) f u n c t i o n // i s empty. void setup ( ) { // s t a r t up t h e l i b r a r y so we can use t h e LED AberLED. begin ( ) ; // c l e a r t h e BACK b u f f e r ( which i s n t d i s p l a y e d ) AberLED. c l e a r ( ) ; // now draw y e l l o w d o t s to t h e back b u f f e r at ( 0, 0) // ( 1, 1 ), ( 2, 2 ) and so on up to (7, 7 ). for ( int i =0; i <8; i ++){ AberLED. s e t ( i, i,yellow) ; // f i n a l l y, swap t h e f r o n t and back b u f f e r s so t h a t t h e // back b u f f e r we j u s t drew i s b e i n g d i s p l a y e d. AberLED. swap ( ) ; // This i s t h e l o o p f u n c t i o n, which runs over and over again // f o r e v e r once t h e s e t u p f u n c t i o n i s complete. In t h i s case // i t s empty so i t does nothing. void loop ( ) { 3

4 2 A moving dot Start a new sketch, and import the AberLED library as before. Put a call to AberLED.begin() in the setup() code. Now, you re going to be working mainly inside the loop() function. First, write a program to just draw one dot. You need to: clear the buffer draw the dot swap the buffers. It s going to look quite like the program above, apart from the drawing part. Make sure this runs. Now modify your program to make the dot move from left to right, wrapping round to the left again once it reaches the right hand edge. Things you ll need to think about: What variables you need, where they should be declared and what initial values they should have. How they change in each tick (i.e. time round the loop). What happens to them when they get to the edge. 2.1 Bouncing the dot Once you ve got that working, try to make the dot fly back and forth between the two edges. Hint: you may need an extra variable here. 4

5 3 Input You can get the current state of a button using AberLED.getButton() with the button number (1-5) as a parameter. This will return non-zero (true) if the button is currently down. For example, this little program will make the red dot appear only when button 2 is down: #include <AberLED. h> void setup ( ) { AberLED. begin ( ) ; void loop ( ) { AberLED. c l e a r ( ) ; i f (AberLED. getbutton ( 2 ) ) { AberLED. s e t ( 0, 0,RED) ; AberLED. swap ( ) ; Now try to modify your program to make it change direction when you press a button. First try reading buttons 2 and 4 to make it change direction from left to right, then add buttons 1 and 3 to make it move up and down as well. Use button 5 to make the dot stop. Do you need any more variables to handle the vertical motion? What should you do when you reach the edges? something). (It s up to you, but you should do 5

6 A Technical details This section is for people who are interested in how the LED hardware works. A.1 Which pins are used The shield uses the following Arduino pins: Digital pins 2-7 are used to drive the LED matrix (see below) Analog pins 0-3 receive input from switches 1-4 Digital pin 9 receives input from switch 5 Digital pin 13 drives the LED (as it does on the Arduino itself) Any pins not in this list are passed through, and you are free to connect to them: digital pins 8 and 10-12; along with analog pins 4 and 5. Don t use digital pins 0 and 1 they re used to talk to the PC. A.2 How the LED matrix works The LED matrix we re using has 24 pins. 8 of these pins are connected to the rows, while the other 16 are connected to the columns one set of 8 for the red LEDs, the rest for the green LEDs. The rows are connected to the anode (positive) side of the LEDs, while the columns are connected to the cathodes (negative). To turn on an LED, we have to connect the cathode to ground and the anode to +5V. You ll notice a lot of resistors on the shield too you can t connect an LED directly, you have to do it through a resistor or a really high current will flow and blow it up 1. So to illuminate (say) the red LED on row 5, column 4 we need to set row 5 to HIGH and red column 4 to LOW. Unfortunately, we can t use this to make a picture if we set more than one row high it would show the same pattern as the other rows, because there isn t a separate set of column lines for each row! This means we can only show one row at a time. We get round this by using persistence of vision. We very quickly turn on each row, showing the columns we want, then turn that off and move on to the next row with different columns lit, and so on. We do this so quickly our eye sees a single picture. Our library does this automatically. 1 Turning your LED (light emitting diode) into an SED (smoke emitting diode). 6

7 A.3 How we control 24 signals with only 6 pins Even with this limitation of all columns sharing the same row data, we still need to control 24 signals. This is more than the Arduino UNO has. To deal with this, we use some very useful ICs called shift registers. With one of these, 3 signals can control 8 outputs. We can also cascade them together, so 3 signals can control 16, 24 or more outputs (but you lose a bit of speed every time you do this). The shield uses three shift registers to control the 24 pins on the matrix, so we only use 6 pins on the Arduino. Two of these are cascaded to form a single, big shift register to control the columns; while one controls the rows, as in Figure 3. row data shift register row data column data shift register green column data red column data shift register column data Figure 3: Shift registers and the LED matrix If you want to know more about shift registers to use in your own projects, there s a handy guide at to get you started. The particular component I m using is the 74HC595. They cost about 35p each! 7