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IMSA Intersession 2011 – Microcontroller Projects

For this year’s Intersession we will design and implement a Persistence of Vision (wikipedia) project.

This posting is my prototype design for the course. The full course documentation can be found at http://code.google.com/p/intersession2011-pov/

POV RevA Build

Build of POV RevA

This project will be based on a PIC18F46k20 microcontroller (link). The firmware for the microcontroller will be written in C and compiled with the MPLAB C18 compiler (link). The functionality of the microcontroller will be used to turn LEDs ON and OFF. Timer modules will be used to sequence timed changing of the LEDs. An EEPROM module will be used to store LED patterns to draw POV designs. Initial POV testing of the design will be battery powered and will be waved by hand. Further testing of the design will involve mounting the design to a motor rotating at 360RPM.

Overview

The idea of this project is to use a microcontroller to create a device that can draw designs in the “air” by illuminating LEDs in sequence as the device moves through a repetitive motion. For this project, our initial repetitive motion will be generated by hand-waving the board through the air.

The example board pictured above has 8 LEDs. Each of these LEDs is independently controllable. The trick is to light the LEDs in a way that a pattern is drawn with the board’s motion.

Linear Motion: Zig Zag

For our first design we will draw a zig-zag pattern using 6 LEDs while waving the board through a linear motion. The algorithm is simple: one LED will be lit at a time, starting at one side of the 6 LEDs and moving toward the other, then the direction will reverse and the pattern will repeat. While this algorithm is running, the student will wave the board through the air. A certain amount of tuning will be required to synchronize the lighting of the LEDs with the movement of the board. This tuning can occur by changing the speed of waving or by modifying the timer interval between LED changes.

POV Linear Zig-Zag

Here is an example program to generate the above pattern. This program assumes the LEDs are all connected such that they ground into PORTB[5:0]. See the Hardware Schematic further down this page for hardware implementation details.
//linear-POV-zigzag.c for IMSAInterssion 2011

#pragma config FOSC = INTIO67
#pragma config WDTEN = OFF, LVP = OFF
#include "p18f46K20.h"

void main (void) {
// We will be shifting 0's in from a side to move the 1 (lit LED)
char pattern = 0b00000001;
char shiftDir = 0; //1 RSHIFT, 0 LSHIFT

// Set TRISB to configure PORTB as OUTPUTS
TRISB = 0;

// Configure the LATB register to set all PORTB outputs HIGH
// Remember: We are grounding the LEDs into the PORT pins.
// The LED will turn on when the pin LATB OUPUT is LOW
LATB = 0xFF;
while (1) {
// Delay some cycles between each LED change
Delay1KTCYx(5);

// We are at one end of the LED string, switch directions
if(pattern == 0b1000000){
// Change shift direction
shiftDir = 1;
}
// We are at the other end, switch directions
else if(pattern == 0b00000001){
//Change shift direction
shiftDir = 0;
}

if(shiftDir == 0){
//Left shift in a 1
pattern = pattern << 1;}

//This blog´s software currently replaces certain characters with ascii command-codes.
// The above should be two left-arrow caret symbols; serving as the LeftShift operator.

else{ //if (shiftDir == 1){
//Right shift in a 1
pattern = pattern >> 1;

//This blog´s software currently replaces certain characters with  ascii command-codes.
// The above should be two right-arrow caret symbols; serving as the RightShift operator.

}

// Set the IO pin Latches
// We need to invert the pattern bit string since
// the LEDs are wired to light when LATB is LOW
LATB = ~pattern;
}
}

Hardware Schematic

The hardware schematic for the example design at the top of this page can be found below. The schematic has the full number of LEDs installed (the example only has the first 8 installed. 6 on PORTB and 2 on PORTD). The microcontroller is configured to use an internal 16MHz oscillator. Connecting the VCC pin from the ICSP connector to the circuit’s VCC bus allows the circuit to be powered from an external programming device (such as a PICKit2) during development. A 2xAA battery compartment is used to power the circuit during operation. Alternatively, this circuit will function from any 3.3V supply.

Schematic for POV RevA Device

Rotational Motion: Zig Zag

For the rotational motion we will mount the board to a motor. I chose to use a salvaged floppy disk motor. The motor control circuitry is configured to provide a 360RPM rotation rate.

Build of the POV RevA.1 design

Here is the zig-zag POV rotational pattern.

This is the zig-zag pattern shown on a POV RevA.1

The only change to the above code was modifying the delay count in the main while loop.

The modified lines should look like:
while (1) {
// Delay some cycles between each LED change
Delay100TCYx(5);

Written by sturnfie

December 26th, 2010 at 5:11 pm

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