'--------Title-------- ' File......robot_cds_line_follow.pbp ' Started....2/29/08 ' Microcontroller used: Microchip Technology PIC16F88 ' microchip.com ' PicBasic Pro Code: micro-Engineering Labs, Inc. ' melabs.com '--------Program Desciption-------- ' The robot uses two CdS photoresistors ' tied to two analog-to-digital converters, ' (AN0 & AN1), to follow a taped line. '------------Comments-------------- '---------PIC Connections--------- ' 16F88 Pin Wiring ' --------- ---------- ' RA0 Center lead CdS voltage divider 1 ' RA1 Center lead CdS voltage divider 2 ' RA4 LCD Register Select(RS) ' RB0 To base of NPN controlling Motor 1 ' RB1 To base of NPN controlling Motor 2 ' RB3 LCD Enable(E) ' RB4 LCD (DB4) ' RB5 LCD (DB5) ' RB6 LCD (DB6) ' RB7 LCD (DB7) ' See schematic for the other usual PIC connections '---------LCD Connections--------- ' LCD Pin Wiring ' --------- ---------- ' 1 Ground(Vss) ' 2 + 5v(Vdd) ' 3 Center of 20K Pot(Contrast) ' 4 RA4(Register Select,RS) ' 5 Ground(Read/Write,R/W) ' 6 RB3(Enable) ' 7 No Connection(DB0) ' 8 No Connection(DB1) ' 9 No Connection(DB2) ' 10 No Connection(DB3) ' 11 RB4(DB4) ' 12 RB5(DB5) ' 13 RB6(DB6) ' 14 RB7(DB7) '---------Revision History-------- '---------Constants/Defines------- ' To free up AN0 and AN1 (Pins RA0 and RA1) for ' an analog input, the default LCD data lines, DB4-DB7, ' function must be removed from RA0 - RA3. ' They are relocated to PORTB.4 - PORTB.7 (RB4-RB7) ' using the LCD DEFINE statements below. All other ' default LCD pins and functions are left unchanged. DEFINE LCD_DREG PORTB 'Sets PORTB as LCD data port DEFINE LCD_DBIT 4 'Start data connections to bit 4 DEFine ADC_BITS 10 'Sets the number of bits in 'the result to 10 '------------Variables------------ left_cds var word 'Word for voltage divider 1 value right_cds var word 'Word for voltage divider 2 value ' As more light enters the CdS photoresistor, the values of left_cds ' and right_cds reduce, an inverse relationship. left_motor var PORTB.0 'Defines PORTB.0 name as left_motor right_motor var PORTB.1 'Defines PORTB.1 name as right_motor '----------Initialization--------- ANSEL = %00000011 'Leaves AN0 & AN1 in analog mode, but 'changes other analog bits to digital. 'See table below. ' Analog Bit Analog or Digital PIC16F88 Pin ' ------------ ------------------ -------------- ' AN0 Analog RA0 ' AN1 Analog RA1 ' AN2 Digital RA2 ' AN3 Digital RA3 ' AN4 Digital RA4 ' AN5 Digital RB6 ' AN6 Digital RB7 ADCON1 = %10000000 'Right justifies 10-bit value of x 'in 16-bit WORD. Adds "0" in the '6 Most Significant bits of the Word, 'shifting the 10-bit value of x to 'the right. OSCCON = $60 'Sets the internal oscillator in the '16F88 to 4 MHz '------------Main Code------------ pause 1000 'Pause to allow LCD to setup start: adcin 0, left_cds 'Read analog voltage on AN0 and 'convert to 10-bit digital value 'and store as left_cds. adcin 1, right_cds 'Read analog voltage on AN0 and 'convert to 10-bit digital value 'and store as right_cds. lcdout $FE,1,"Left CdS = ", dec left_cds 'Clears LCD screen, displays '"Left CdS = " and the 10-bit 'value of left_cds lcdout $FE,$C0,"Right CdS = ", dec right_cds 'LCD jumps to beginning of second 'line and displays "Right CdS = " 'and the 10-bit value of right_cds if (left_cds >= 900) then turnleft 'If the left_cds value is greater 'than or equal to 900, the robot 'turns to the left. if (right_cds >= 900) then turnright 'If the right_cds value is greater 'than or equal to 900, the robot 'turns to the right. high left_motor 'If neither of the CdS photocells high right_motor 'values are greater than or equal pause 5 'to 900, the robot travels forward. goto start 'Go to start label turnright: high left_motor 'Turn on left motor (RB0) low right_motor 'Turn off right motor (RB1) pause 5 'Pause 5 mS goto start turnleft: low left_motor 'Turn off left motor (RB0) high right_motor 'Turn on right motor (RB1) pause 5 'Pause 5 mS goto start end