//*********************************************************
/*  Junebug_Serial4.c    RomanBlack.com 19th July 2009.

	Junebug 18F1320, uses my "zero error 1 second timer"
	system to generate a 2 second interval, then every
	2 seconds it reads an analog voltage from a
	Sharp GP2 distance sensor and converts it to decimal
	distance, then sends that data as a text string to PC
	via bitbanged serial out. It also flashes Junebug LED1
	everytime it takes a distance sample.

	Code for MikroC, config handled by MikroC compiler;
	_INTI02_OSC_1H
	_WDT_OFF_2H
	-MCLRE_ON_3H
	_LVP_OFF_4L
	_PWRT_ON_2L

*/
//*********************************************************

// functions declared
void calc_distance(void);
void send_serial_message(void);
void send_serial_byte(unsigned char);

#define PIN_SER_OUT LATA.F3		// which pin for serial out (PORTA.F3)
#define SER_BAUD 51				// TMR3 (1Mhz/19200 baud) = 52
								// tested; works from 49 to 53, using 51

unsigned char i;		// used for looping

unsigned char cm10;		//
unsigned char cm;		//

unsigned int math;		// used for voltage calculations
unsigned long bres;		// for bresenham 2-second timer system


//---------------------------------------------------------
void main()
{
	// setup the PIC 18F1320
	OSCCON = 0x72;      	// internal osc, 8MHz

	PORTA = 0;
	TRISA = 0b10000010; 	// RA7 high imp, RA3 is serial out,
							// RA1 is ADC input measuring VR1
	PORTB = 0;
	INTCON2 = 0;            // PORTB pullups ON
	TRISB = 0b00000000; 	// PORTB not used

	ADCON0 = 0b00000101;	// ADC ON, RA1 is ADC input
	ADCON1 = 0b01111101;	// AN1 is ADC input
	ADCON2 = 0b10100010;	// right justify, 8Tad, 32Tosc
	T1CON = 0b00010001;     // TMR1 is ON, 1:2 prescale, =1MHz

	T3CON = 0b00010001;     // TMR3 is ON, 1:2 prescale, =1MHz

	// main loop here;
	while(1)
	{
		// wait for 2 seconds, uses TMR1 free running at 1Mhz
		while(!PIR1.TMR1IF);    // wait for TMR1 overflow
        PIR1.TMR1IF = 0;		// clear overflow flag
		LATA = 0;				// all LEDs off
		
		bres += 65536;			// add 65536uS to bres value
		if(bres >= 2000000)		// if reached 2 seconds!
		{
			bres -= 2000000;	// subtract 2 seconds, keep error
		
			// flash Junebug LED1,  RA0=1 RA6=0 RA7=hiimpedance
			LATA.F0 = 1;			// LED on

		    // read the ADC voltage RA1 (Sharp GP2 sensor)
		    ADCON0.F1 = 1;		// set GO bit, start doing ADC
		    while(ADCON0.F1);	// wait until ADC done
			calc_distance();		// convert ADC value to distance
			send_serial_message();	// send message back to PC!
		}

	}
}



//---------------------------------------------------------
void calc_distance(void)
{
	// from the Sharp datasheet the analog voltage is
	// the inverse of distance, so distance can be calculated
	// d = (1 / volts) then just scaled to suit the sensor

	// load ADC value in 16bit math var
	math = ADRESH;
	math = (math * 256);
	math += ADRESL;

	// now invert it; (1 / volts) use (6050 / volts) for scaling
	math = (6050 / math);
	if(math >= 2) math -=2;		// fix linear error (-2)
	if(math > 99) math = 99;	// max limit at 99cm

	// convert from 0-99 to 2 decimal digits, 0-99cm
	cm10=0;
	while(math >= 10)
	{
		cm10++;
		math -= 10;
	}
	cm = math;
}


//---------------------------------------------------------
void send_serial_message(void)
{
	// send message and number to serial port
	send_serial_byte('J');			// send ascii text
	send_serial_byte('u');
	send_serial_byte('n');
	send_serial_byte('e');
	send_serial_byte('b');
	send_serial_byte('u');
	send_serial_byte('g');
	send_serial_byte(' ');

	send_serial_byte('G');
	send_serial_byte('P');
	send_serial_byte('2');
	send_serial_byte('=');

	send_serial_byte('0'+ cm10);	// send number as ascii text 0-9
	send_serial_byte('0'+ cm);	// send number as ascii text 0-9
	send_serial_byte('c');
	send_serial_byte('m');

	send_serial_byte(13);			// send carriage return/linefeed pair
	send_serial_byte(10);			//  to start a new text line

}


//---------------------------------------------------------
void send_serial_byte(unsigned char data)
{
	// this manually sends a serial byte out any PIC pin.
	// NOTE! serial is inverted to connect direct to PC serial port.
	// baud timing is done by using TMR3L and removing
	// timer error after each baud.

	i=8;						// 8 data bits to send

	PIN_SER_OUT = 1;			// make start bit
	TMR3L = (256 - SER_BAUD);	// load TMR3 value for first baud;
	while(TMR3L.F7);			// wait for baud

	while(i)			// send 8 serial bits, LSB first
	{
		if(data.F0) PIN_SER_OUT = 0;    // invert and send data bit
		else		PIN_SER_OUT = 1;

		data = (data >> 1);			// rotate right to get next bit
		i--;
		TMR3L -= SER_BAUD;      // load corrected baud value
		while(TMR3L.F7);        // wait for baud
	}

	PIN_SER_OUT = 0;		// make stop bit
	TMR3L -= SER_BAUD;		// wait a couple of baud for safety
	while(TMR3L.F7);
	TMR3L -= SER_BAUD;
	while(TMR3L.F7);
}

TRISA = 0b10000010; 	// RA7 high imp, RA3 is serial out,
			// RA1 is  

ADCON2 = 0b10100010;	// right justify, 8Tad, 32Tosc