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4.c. Using the Preloaded Demo Program
Your 3pi comes preloaded with a program that demonstrates most of its features and allows you to test that it is working correctly. When you first turn on your 3pi, you will hear a beep and see the words “Pololu 3pi Robot”, then “Demo Program” appear, indicating that you are running the demo program. If you hear a beep but do not see any text on the LCD, you may need to adjust the contrast potentiometer on the underside of the board. When the program has started successfully, press the B button to proceed to the main menu. Press C or A to scroll forward or backward through the menu, and press B to make a selection or to exit one of the demos. There are seven demos accessible from the menu:
- Battery: This demo displays the battery voltage in millivolts, which should be above 5000 (5.0 Volts) for a fully-charged set of batteries. Removing the jumper marked ADC6 will separate the battery voltage measurement circuit from the analog input, causing the number displayed to drop to some low value.
- LEDs: Blinks the red and green user LEDs on the underside of the board. If you have soldered in the optional user LEDs, they will also blink.
- Trimpot: Displays the position of the user trimmer potentiometer, which is located on the underside of the board, as a number between 0 and 1023. While displaying the value, this demo also blinks the LEDs and plays a note whose frequency is a function of the current reading. It is easiest to turn the trimpot using a 2mm flat-head screwdriver.
- Sensors: Show the current readings of the IR sensors using a bar graph. Bigger bars mean lower reflectance. Placing a reflective object such as your finger under one of the sensors will cause the corresponding reading to drop visibly on the graph. This demo also displays “C” to indicate that button C has an effect—press C and the IR emitters will be turned off. In indoor lighting conditions away from bright incandescent or halogen lights, all of the sensors should return entirely black readings with IR off. Removing the jumper marked PC5 disables control of the emitters, causing them to always be on.
- Motors: Hold down A or C to run the motor on the corresponding side, or hold down both buttons to run both motors simultaneously. The motors will gradually ramp up to speed; in your own programs, you can switch them on much more suddenly. Tap A or C to switch the corresponding motor to reverse (the button letter becomes lowercase if pressing it will drive the corresponding motor in reverse).
- Music: Plays an adaptation of J. S. Bach’s Fugue in D Minor for microcontroller and buzzer, while scrolling a text display. This demonstrates the ability of the 3pi to play music in the background.
- Timer: A simple stopwatch. Press C to start or stop the stopwatch and A to reset. The stopwatch continues to count while you are exploring the other demos.
Note: If the 3pi receives any serial data while the demo program is waiting for a button press from the user, it will switch into serial slave mode. See Section 10.a for more information.
The source code for the demo program is included with the Pololu AVR C/C++ Library described in Section 6, in the folder