C Electronics Microcontrollers

AD5246 I2C Digital Resistor+PIC 16F1509 Test Circuit

As part of a larger MIDI project I was looking for some digital resistors. With any project I try to tackle the parts I think I’m going to have the most problem with first, of course it rarely works out I choose the difficult bits… this was the case with these resistors, they’re super simple.

A simple circuit with the PIC dev board, the SC70-6 i2C resistor and some pull up resistors (don't forget those!) I'm running 5V using 10k here..
A simple circuit with the PIC dev board, the SC70-6 i2C resistor and some pull up resistors (don’t forget those!) I’m running 5V using 10k here..

My last adventure with I2C took me a while to beat into submission so I thought I would start with this. I have ordered a enough SOIC/SC70/TSSOP, etc. breakout boards to be considered borderline hoarding. All the fun stuff comes in small packages which makes sense for placing it in a product but it’s no fun when you’re just trying to check something out. I recommend grabbing some if you haven’t already. I’m not brave enough to shoot from the hip and have boards fabed without at least testing the stuff I’m questionable about… granted in this case I2C hardware is pretty simple.  I popped my first Analog Devices AD5246BKSZ10 (Digi-Key Part number: AD5246BKSZ10-RL7CT-ND )  on to a little SIP package breakout board.. I eventually gave up on the SIP package. I hand-soldered it and it must have had some little bits under the package. I grabbed a DIP package breakout and threw some chipquick down then used my 858D to reflow the tiny SC70-6 package.

A little breakout board, I bought a ton of these on eBay for SC70-6 and others..
A little breakout board, I bought a ton of these on eBay for SC70-6 and others..

On power up the resistor defaults to mid-span (with no command).. that’s kind of nice but I will have to consider that when integrating this to a project; In my case that is 5K (of 10k). I hacked up some recent I2C code for quick dev … it was a no-brainer really. The 10K resistor I have centers out at 5.00K but its top side is 9.90K .. not a big deal for me. The resistance data command is 7bit, 0x00 to 0x7F takes you from 0 Ohms to 10K. If you did the math that’s 78 Ohm steps… There is a 5K, 10K, 50K and a 100K version in this series and they can only handle 5mA of current. I will consider putting in a typical passive resistor in series to limit the possible current through the resistor if that will be an issue.

Some thoughts I had..

Pros:

  • Easily adaptable to an all analog circuit
  • tiny!
  • great for firmware calibration! no tiny pots in a case you have to open
  • Doesn’t power up at 0 Ohm!  (this might be  a con for you..)

Cons:

  • Not addressable (it’d be nice if it was a 8 pin package to select between 4 different addresses)
  • Tiny package if you’re trying to hand-solder a project
  • No so good if you need very fine resolution

 

No surprises really.. So here’s the goodies: a screen shot of the I2C write command for max resistance followed by the code.

The i2c command was super simple, start, address,n a 7-bit value 0x00 - 0x7F, stop!
The i2c command was super simple, start, address,n a 7-bit value 0x00 – 0x7F, stop!

 

 


/* 
 * File:   main.c
 * Author: Charles M Douvier
 * Contact at: http://iradan.com
 *
 * Created on September 14, 2014, 8:06 AM
 *
 * Target Device:
 * 16F1509 on Tautic 20 pin dev board
 *
 * Project: Digital Resistor Test
 *
 *
 * Version:
 * 1.0  Initial Code to Test Wiper
 *
 *
 *  AD5246BKSZ10-RL7
 *  I2C Address 0x5C (Write)
 *  Resistor I2C
 *  Write S 0 1 0 1 1 1 0 W A X D6 D5 D4 D3 D2 D1 D0 A P
 *  Read  S 0 1 0 1 1 1 0 R A 0 D6 D5 D4 D3 D2 D1 D0 A P
 */
#ifndef _XTAL_FREQ
#define _XTAL_FREQ 4000000 //4Mhz FRC internal osc
#define __delay_us(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000000.0)))
#define __delay_ms(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000.0)))
#endif

#include 
#include 
#include 
#include 

//config bits
#pragma config FOSC=INTOSC, WDTE=OFF, PWRTE=ON, MCLRE=ON, CP=OFF, BOREN=OFF, CLKOUTEN=OFF, FCMEN=OFF
#pragma config WRT=OFF, STVREN=OFF, LVP=OFF

#define _XTAL_FREQ 4000000 //defined for delay

    unsigned int ACK_bit;
    int i;
    unsigned char byte, tempbyte1, tempbyte2;

/*
 * 
 */
void init_io(void) {

    ANSELA = 0x00; // all port A pins are digital I/O
    ANSELB = 0x00; // all port A pins are digital I/O
    ANSELC = 0x00; // all port B pins are digital I/O

    TRISAbits.TRISA0 = 0; // output
    TRISAbits.TRISA1 = 0; // output
    TRISAbits.TRISA2 = 0; // output
    TRISAbits.TRISA3 = 0; // output
    TRISAbits.TRISA4 = 0; // output
    TRISAbits.TRISA5 = 0; // output

    TRISBbits.TRISB4 = 1; // RB4 I2C SDA, has to be set as an input
    TRISBbits.TRISB5 = 1; // RB5 = nc
    TRISBbits.TRISB6 = 1; // RB6 I2C SCLK, has to be set as an input
    TRISBbits.TRISB7 = 0; // RB7 = nc

    TRISCbits.TRISC0 = 0; // output
    TRISCbits.TRISC1 = 0; // output
    TRISCbits.TRISC2 = 0; // output
    TRISCbits.TRISC3 = 0; // output
    TRISCbits.TRISC4 = 0; // output
    TRISCbits.TRISC5 = 0; // output
    TRISCbits.TRISC6 = 1; // input
    TRISCbits.TRISC7 = 1; // input
}


void I2C_ACK(void)
{
   PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
   SSP1CON2bits.ACKDT=0;        // clear the Acknowledge Data Bit - this means we are sending an Acknowledge or 'ACK'
   SSP1CON2bits.ACKEN=1;        // set the ACK enable bit to initiate transmission of the ACK bit to the serial eeprom
   while(!PIR1bits.SSP1IF);    // Wait for interrupt flag to go high indicating transmission is complete
}

void Send_I2C_Data(unsigned int databyte)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSPBUF = databyte;              // send databyte
    while(!PIR1bits.SSP1IF);    // Wait for interrupt flag to go high indicating transmission is complete
}

unsigned char RX_I2C_Data (void)
{

    RCEN = 1;               //
    while( RCEN ) continue;
    while( !BF ) continue;
    byte = SSPBUF;
   return byte;
}

void I2C_Control_Write0(void)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSP1BUF = 0x5C;             // send the control byte (90 TCN75, EF BMP085)
    while(!PIR1bits.SSP1IF)     // Wait for interrupt flag to go high indicating transmission is complete
        {
        i = 1;
          // place to add a breakpoint if needed
        }
    PIR1bits.SSP1IF=0;

}
void I2C_Control_Write1(void)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSP1BUF = 0x92;             // send the control byte (90 TCN75, EF BMP085, change this)
    while(!PIR1bits.SSP1IF)     // Wait for interrupt flag to go high indicating transmission is complete
        {
        i = 1;
          // place to add a breakpoint if needed
        }
    PIR1bits.SSP1IF=0;

}

void I2C_Control_Read0(void)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSP1BUF = 0x91;             // send the control byte (90 TCN75, EF BMP085, change this)
    while(!PIR1bits.SSP1IF)     // Wait for interrupt flag to go high indicating transmission is complete
        {
        i = 1;
          // place to add a breakpoint if needed
        }
    PIR1bits.SSP1IF=0;
   }



void I2C_Start_Bit(void)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSPCON2bits.SEN=1;          // send start bit
    while(!PIR1bits.SSP1IF)    // Wait for the SSPIF bit to go back high before we load the data buffer
        {
        i = 1;
        }
    PIR1bits.SSP1IF=0;
}

void I2C_check_idle()
{
    unsigned char byte1; // R/W status: Is a transfer in progress?
    unsigned char byte2; // Lower 5 bits: Acknowledge Sequence, Receive, STOP, Repeated START, START

    do
    {
        byte1 = SSPSTAT & 0x04;
        byte2 = SSPCON2 & 0x1F;
    } while( byte1 | byte2 );
}
/*
 * Send the repeated start message and wait repeated start to finish.
 */
void I2C_restart()
{
    I2C_check_idle();
    RSEN = 1; // Reinitiate start
    while( RSEN ) continue;
}

void I2C_Stop_Bit(void)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSPCON2bits.PEN=1;          // send stop bit
    while(!PIR1bits.SSP1IF)
    {
        i = 1;
        // Wait for interrupt flag to go high indicating transmission is complete
    }
}

void I2C_NAK(void)
{
    PIR1bits.SSP1IF=0;           // clear SSP interrupt bit
    SSP1CON2bits.ACKDT=1;        // set the Acknowledge Data Bit- this means we are sending a No-Ack or 'NAK'
    SSP1CON2bits.ACKEN=1;        // set the ACK enable bit to initiate transmission of the ACK bit to the serial eeprom
    while(!PIR1bits.SSP1IF)     // Wait for interrupt flag to go high indicating transmission is complete
    {
        i = 1;
    }
}

void set_resistor(void)
{

    I2C_Start_Bit();                    // send start bit
    I2C_Control_Write0();               // send control byte with read set
    Send_I2C_Data(0x7F);                // Send Resistance Value Data
                                        // 0x00 - 0x7F
                                        // 0 - 10KOhm
    I2C_Stop_Bit();                     // Stop

}




int main(void) {

    // set up oscillator control register, using internal OSC at 4MHz.
    OSCCONbits.IRCF = 0x0d; //set OSCCON IRCF bits to select OSC frequency 4MHz
    OSCCONbits.SCS = 0x02; //set the SCS bits to select internal oscillator block
    OPTION_REGbits.nWPUEN = 0; // enable weak pullups (each pin must be enabled individually)

    SSPCONbits.SSPM=0x08;       // I2C Master mode, clock = Fosc/(4 * (SSPADD+1))
    SSPCONbits.SSPEN=1;         // enable MSSP port
    SSPADD = 0x09;              // 100KHz
    // **************************************************************************************

    init_io();

    __delay_ms(100);             // let everything settle.

    set_resistor();

    while (1) {
        //do something
        PORTAbits.RA0 = 0;
        __delay_ms(100);
        PORTAbits.RA0 = 1;
        __delay_ms(100);
    }
    return (EXIT_SUCCESS);
}


 

Electronics Motors VFD

Electric Scooter & new VFD update

I finally got my brother over to do some welding for me. The electric scooter is only a couple of nuts and bolts away from a complete frame. I have the core electronics finished .. so maybe this weekend I’ll be able to take it for my first test drive… I can tell I’ll need to extend my handle bar.. but that can wait for another day.

 

Work continues on the electric scooter... I got my brother to weld for me because he is better at it (but don't tell him that).
Work continues on the electric scooter… I got my brother to weld for me because he is better at it (but don’t tell him that).

The frame I build out of over priced metal stock from Home Depot.. (most of it is under the vehicle in the above photo) .. the front end is from a kid’s bike.. The motor and drive have already checked out.. don’t know what kind of speed I’ll get out of it, I doubt over 15mph or so.

 

I also scored another VFD today. It’s another Rockwell Automation VTAC9 but this one is much smaller and very bench-friendly. I have about 280VDC on the bus and I got it power up into precharge (kicks on at about 250VDC). I have another 90VDC in batteries and I thought another case (so 180V.).. I hope that’s enough to get me out of precharge or I’ll have to build a high voltage DC power supply. meh. I couldn’t finish my testing because my brother has shown up for the welding.

I scored another VFD. This one has a crap AC input but driving the DC bus direct works just fine as it has on all Rockwell Automation drives I've tried.
I scored another VFD. This one has a crap AC input but driving the DC bus direct works just fine as it has on all Rockwell Automation drives I’ve tried.

It’s front end (AC input) is dead but it looks like I can chop some jumpers to disconnect it. Though I had it hooked up when I ran up the DC input. I was running about 50 mA with the fans and UI running.  If you have one with no wires attached .. mine starts up with Terminal 1, 3, 4, 5, 6 and 7 jumpered and Terminal 8 and 9 jumpered. This base doesn’t have a “DC -” terminal like the large drive has.. so you can either tie it to the big DC bus jumpers off the capacitor board or there is a DC+ terminal and the DC- is a little single test point pin to the right of the terminals. If I have enough VDC in this house maybe I’ll be spinning a motor by the end of the week. I reprogrammed the drive already… it’s pretty self-explanatory.

 

Update: 402 VDC… still in pre-charge. I have a 150VDC power supply I’ll did out. I’m hoping 550V will do the trick.. 600VDC is nominal.

C Electronics Interface RS-232

Using Parity on the PIC 18F26K22 UART

I have been working on the next article for 0xEE.net this weekend while I recover from my week long backpacking trip. My muscles are feeling great but I took a couple good hits from sharp boulders while doing some Class 2-3 scrambling. It was well worth it of course.

A view of the lake I stayed on after a bit of a scramble up the hill.
A view of the lake I stayed on after a bit of a scramble up the hill.

In the article I’m working on I used parity on a UART. I wanted to share this snippet with you in case you ran into the same thing. I’ve never used parity with the PICs and was a little surprised to find no built in parity checking function; it’s not that big of a deal of course.. I haven’t even ever really looked. At least they allow for a 9-bit mode so you can perform your own software parity checking. No bit-banging for me this weekend. In the code below I am transmitting at a crawl.. 2,400 baud 8E1 (You’ll find out why in a while if you follow 0xEE.net). I’ll drop the receiving code here but the transmitting side uses the same code.. except I did it on a 16F1509 but the parity function is exactly the same. I feel a little embarrassed I pulled this parity function itself from the internet and forgot where I sourced it; everything else is mine. I had kept the FireFox window open to grab the URL for reference but forgot to grab it before a Windows Update restart. Regardless it was just snippet on a forum somewhere; there are a couple different versions of the same thing or lookup tables.. I felt this was the most elegant method.

 

The biggest change to normal UART use was  enabling 9 bit mode. Both on the RX and the TX side… In this case for the RX micro I didn’t need to set the TXSTA1bits.TX9 because I’m only doing one way communication but I felt it was good for consistency.

TXSTA1bits.TX9=1; // select 9 data bits for TX

RCSTA1bits.RX9=1; // select 9 data bits for RX

One of the benefits to this particular parity code is it’s none destructive. I’ve seen more code that decimates the original variable than doesn’t. Not a big deal if you’re like me and your micros are always loafing around.

You can take this code and drop it on a TAUTIC 18F26K22 development board.. RA0 is the onboard LED.

Finally, the complete RX code:



/*
 * File:   main.c
 * Author: Charles M Douvier
 * Contact at: http://iradan.com
 *
 * Created on Sept 1 2014, 12:12 PM
 *
 * Target Device:
 * 18F26K22 TAUTIC dev board
 *
 * Project:
 *
 *
 * Version:
 * 1.0
 *
 */
#ifndef _XTAL_FREQ
#define _XTAL_FREQ 4000000 //4Mhz FRC internal osc
#define __delay_us(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000000.0)))
#define __delay_ms(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000.0)))
#endif

#include 
#include 
#include 
#include 


//config bits
#pragma config FOSC=INTIO67, WDTEN=OFF, PWRTEN=OFF, CP0=OFF, CP1=OFF, BOREN=ON
#pragma config STVREN=ON, LVP=OFF, HFOFST=OFF, IESO=OFF, FCMEN=OFF

//WRT=OFF, FOSC=INTOSC, MCLRE=ON

#define _XTAL_FREQ 4000000 //defined for delay


    char    buf[10];            //buff for iota
    char    parity_rx, rx_data;


    volatile unsigned int uart_data, parity;    // use 'volatile' qualifer as this is changed in ISR
/*
 *
 */
void interrupt ISR() {

    if (PIR1bits.RCIF)          // see if interrupt caused by incoming data
    {
        parity_rx = RCSTA1bits.RX9D;  //grab parity bit first
        uart_data = RCREG;     // read the incoming data
        PIR1bits.RCIF = 0;      // clear interrupt flag
    }

}

void init_io(void) {
    TRISAbits.TRISA0 = 0; // output
    TRISAbits.TRISA1 = 0; // output
    TRISAbits.TRISA2 = 0; // output
    TRISAbits.TRISA3 = 0; // output
    TRISAbits.TRISA4 = 0; // output
    TRISAbits.TRISA5 = 0; // output


    ANSELA = 0x00; // all port A pins are digital I/O


    TRISBbits.TRISB4 = 0; // RB4 = nc
    TRISBbits.TRISB5 = 1; // RB5 = nc
    TRISBbits.TRISB6 = 0; // RB6 = nc
    TRISBbits.TRISB7 = 0; // RB7 = nc

    ANSELB = 0b00001000;     //RB3, AN9

    TRISCbits.TRISC0 = 0; // output
    TRISCbits.TRISC1 = 0; // output
    TRISCbits.TRISC2 = 0; // P1A PWM output
    TRISCbits.TRISC3 = 0; // output
    TRISCbits.TRISC4 = 0; // output
    TRISCbits.TRISC5 = 0; // output
    TRISCbits.TRISC6 = 1; // input
    TRISCbits.TRISC7 = 1; // input
    ANSELC = 0x00; // all port B pins are digital I/O
}

//not of my code.. 
unsigned char calculateparity(unsigned char scancode)
{
	unsigned char parity = 0;

	while(scancode > 0)          // if it is 0 there are no more 1's to count
	{
		if(scancode & 0x01)    //see if LSB is 1
		{
			parity++;                // why yes it is
		}
		scancode = scancode >> 1; //shift to next bit
	}

	return (parity & 0x01);  // only need the low bit to determine odd / even }
}

void uart_xmit(unsigned int mydata_byte) {

    while(!TXSTA1bits.TRMT);    // make sure buffer full bit is high before transmitting
    TXREG = mydata_byte;       // transmit data
}

void serial_init(void)
{
    //2400 8E1
    // calculate values of SPBRGL and SPBRGH based on the desired baud rate
    //
    // For 8 bit Async mode with BRGH=0: Desired Baud rate = Fosc/64([SPBRGH:SPBRGL]+1)
    // For 8 bit Async mode with BRGH=1: Desired Baud rate = Fosc/16([SPBRGH:SPBRGL]+1)



    TXSTA1bits.BRGH=1;       // select low speed Baud Rate (see baud rate calcs below)
    TXSTA1bits.TX9=1;        // select 9 data bits
    TXSTA1bits.TXEN = 1;     // enable transmit


    RCSTA1bits.SPEN=1;       // serial port is enabled
    RCSTA1bits.RX9=1;        // select 9 data bits
    RCSTA1bits.CREN=1;       // receive enabled

    /*
     *bit 2 FERR: Framing Error bit
     *1 = Framing error (can be updated by reading RCREGx register and receive next valid byte)
     *0 = No framing error
     *bit 1 OERR: Overrun Error bit
     *1 = Overrun error (can be cleared by clearing bit CREN)
     *0 = No overrun error
     *bit 0 RX9D: Ninth bit of Received Data
     *This can be address/data bit or a parity bit and must be calculated by user firmware.
     */

    SPBRG1=103;  // here is calculated value of SPBRGH and SPBRGL
    SPBRGH1=0;

    PIR1bits.RCIF=0;        // make sure receive interrupt flag is clear
    PIE1bits.RCIE=1;        // enable UART Receive interrupt
    INTCONbits.PEIE = 1;    // Enable peripheral interrupt
    INTCONbits.GIE = 1;     // enable global interrupt

         __delay_ms(50);        // give time for voltage levels on board to settle

}

int main(void) {

    init_io();
    serial_init();


    // set up oscillator control register, using internal OSC at 4MHz.
    OSCCONbits.IRCF = 0x05; //set OSCCON IRCF bits to select OSC frequency 4MHz
    OSCCONbits.SCS = 0x02; //set the SCS bits to select internal oscillator block



    while (1) {
        PORTAbits.RA0 = 0;
        if (uart_data) {

            if (RCSTA1bits.FERR) {  // Frame Error, next read will reset
                uart_data = NULL;
            }

            if (RCSTA1bits.OERR) {  // Overrun Error
                RCSTA1bits.CREN=0;       // receive disabled
                __delay_us(1);
                RCSTA1bits.CREN=1;       // receive enabled
                uart_data = NULL;
            }

            parity = calculateparity(uart_data);
            if (parity_rx == parity) {

                rx_data = uart_data;
                if (rx_data == 'a') {
                    PORTAbits.RA0 = 1;
                    __delay_ms(1);
                    PORTAbits.RA0 = 0;
                }
            }


            uart_data = NULL;   //Done
        }


 //       PORTAbits.RA0 = 1;
 //       __delay_ms(40);
 //       PORTAbits.RA0 = 0;
 //       __delay_ms(40);


    }
    return (EXIT_SUCCESS);
}

Electronics

Introducing Snohomish County Electronics Hobbyist Association

I have built this website in hopes of forming a Snohomish County (North Seattle/Everett) electronics club.

The Snohomish County Electronics Hobbyist Association

I hope to grow at least a small group of interested people for meetings.. then if we have enough interest a HackerSpace, maybe some classes, etc could follow.

Contact me if you’d like to get in on the action and help me put this together.

Uncategorized

Snohomish County HackerSpace/MakerSpace?

I wonder if there is any interest in setting up a North Seattle/SnoCo hackspace? I’m talking Lynnwood, Bothell, Everett area? Or perhaps even just an “electronics-embedded dev club” of sorts. Everything in the Seattle area is seemingly below I-90. Primary interests would be electronics, embedded development, perhaps some machining.

Send me a message or reply if you have any interest or even if you live north of Seattle and think it’s a poor idea for some reason?

 

Analog Electronics Radio RF

Amidon Toriod Experimenter Kits

I have been pushing myself to build some IF filters. I’ve never built a front end of a radio; VCO, mixer, filters.. none of it. I started by buying the Amidon Toroid Experimenters kit #2 and #3 as many of the ARRL handbook samples use Amidon part numbers. I ended up switching to another book to do all my research though; “Secrets of RF Design”. Let me let you in on the secret.. it’s a lot of reading, not all of it stimulating. I also bought the “Island Cutter” from QRPme which is probably one of my favorite purchases of the year… armed with that I started building circuits.

If you’re working about purchasing the Amidon Experimenter Kits.. well I have no regrets. It gave me a good selection of options and even some larger one’s I don’t know when I will use but maybe for a switching supply project or something. I ordered a few other small pieces I knew I’d need more than 4 of just to have them on hand.

Amidon Toroid Kits

I really enjoy the circuits around varactor diodes. I’m building an analog front end but for stability I might just end up wwitching to DDS later on but for now for the VCO is a tank circuit. Next step is the mixer..

Varactor Tank Circuit Fun

 

I probably should still be working on other things, I have a pile of “to-do”s but I needed a little inspiration to keep me at the bench after all this summer fun. My last summer outing is a 7 day backpacking trip in the northern cascades packrafting! That’ll be some seriously needed unplug time. So stay tuned… I ordered about ~$500 worth of electronics for all my up-coming fun.. looking forward to digging into it. I still need to buy an LCR meter, I’ve never owned one and it would be nice to know my inductors is/are “in the ball field” when I wind something using the tables… I can do the math but I think it’d still be nice for a confirmation before I start soldering and making measurements.

C Electronics GPS PIC Time

WWVB signal generated from GPS

I sat at the bench this morning waiting for the inspiration to continue on with a project I’m working on with Francesco; I gave in to procrastination.

I wrote some assembler code to generate WWVB signal from a PIC a few months ago, remember? That stirred some interest from overseas folks looking for a way for their automatically update their “atomic” watches… apparently there isn’t some NTP device or anything else easily found to be purchased to do this. I was asked to do this NTP, but I’ll leave that for someone with a ‘Pi–I gave mine away to a kid. I did this project using GPS and a PIC micro.

It’s a pretty simple setup, gobble up a GPRMC sentence, pick off the data I need and spit out time. I generate 60KHz with the PWM module within the PIC (okay it’s 62KHz, but that should be close enough).. switch it through a 4066 to generate my time code.

GPRMC: there are other sentences you can use, but my cheapo module only spits out 4 sentences and GPRMC is the only one with time and date, so it’ll do. I re-used my GPGGA parsing code.. there is probably some left-overs in there if you look at the code below. I also dump the working string (first 63 bits of GPGGA) followed by the day number of the year which is calculated on the the UART, pick it up off the TX line @ 9,600 baud.. It’s spits it out about once a minute (in between time transmissions). I ended up using some DOY code online because I found some nice code that included determining if it was a leap year for day-of-year determination; I left the URL in the code.

The code isn’t finished nor is it accurate: it doesn’t recognize the valid data bit yet, and just spits out time whenever it feels like it so the time can be off by up to 59 seconds. I’ll work on this later on since I was just looking for proof of concept so I could get the hardware going and off a breadboard. I built up the circuit in eagle.. I’ll check it a few more times and have a couple PCBs made for round one of testing. The prototype was built on a Tautic 18F26K22 dev board, I considered just having the dev board plug-in but that’s probably a waste of $$.

You’ll note the SMA jack, perhaps this is over kill since I’ll never have a good enough antenna to match 60KHz… I don’t really know what to do with that yet, wire antenna for now I suppose. (version 2?) It’s likely illegal to sell these since it’s purposefully broadcasting, fat chance I’m doing the research beyond the FCC. I’ll look it up tomorrow but I suspect Part 15 doesn’t apply to 60KHz.

Version 1 of the GPS>WWVB board
Version 1 of the GPS>WWVB board

 

The code is a total hack job.. poorly documented, perhaps even incorrectly documented. I know I have “place-holder” functions.. but like I said..  it was a start to get my time code and it was close enough for testing; you get what you pay for! :)

 

/*
 * File:   main.c
 * Author: Charles M Douvier
 * Contact at: http://iradan.com / 0xEE.net / @chasxmd
 * Created on April 4th, 2014
 *
 * Target Device: 18F26K22
 *
 * Project: GPS --> WWVB simulator
 *
 * This version uses the GPRMC block
 * This is a limitation because GPRMC doesn't pass seconds
 * The time passed will always be up to 60 seconds off
 * I have to deterine DDMMYY --> Day of year, year
 * No simple leap year info in GPS :(
 *
 * TODO
 * Determine GPS lock and output to LED
 * Consider re-writing how I am writing my time code
 *
 * I'll re-write this sometime with a better (more expensive) GPS module.
 *
 * Version:
 * 0.1      First build I could prove I had GPS lock
 * 0.2      Output time/date on 232
 *
 */
#ifndef _XTAL_FREQ
#define _XTAL_FREQ 8000000 //4Mhz FRC internal osc
#define __delay_us(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000000.0)))
#define __delay_ms(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000.0)))
#endif

#include 
#include 
#include 
#include 


//config bits
#pragma config FOSC=INTIO67, WDTEN=OFF, PWRTEN=OFF, CP0=OFF, CP1=OFF, BOREN=ON
#pragma config STVREN=ON, LVP=OFF, HFOFST=OFF, IESO=OFF, FCMEN=OFF

//WRT=OFF, FOSC=INTOSC, MCLRE=ON

#define _XTAL_FREQ 8000000 //defined for delay

    char    ctxt[120], wstr[120];            //buff NMEA string, working string
    char    str1[20], str2[20], c, latstr, lonstr, setstr, doych[8];
    char    hourch[3], minch[3], secch[3], daych[3], monthch[3], yearch[3];
    char buffer[32] = "none";                        //temp dump
    volatile unsigned int     ping, isrcall, index, reading, new_rx;
    int     ready, gpgga, gprmc, mode;        //gps associated vars
    int     leap_year, dayint, monthint, yearint, year4int, secondint, minuteint, hourint;
    long    doy;
    int     min_40, min_20, min_10, min_8, min_4, min_2, min_1;
    int     hour_20, hour_10, hour_8, hour_4, hour_2, hour_1;
    int     doy_200, doy_100, doy_80, doy_40, doy_20, doy_10;
    int     doy_8, doy_4, doy_2, doy_1, leapint;
    int     year_80, year_40, year_20, year_10, year_8, year_4, year_2, year_1;

    //char    *rxdata;
    //volatile unsigned int uart_data;    // use 'volatile' qualifer as this is changed in ISR

/*
 *  Interrupt Service
 */
void interrupt ISR() {

   if (PIR1bits.RCIF){          // see if interrupt caused by incoming data

        isrcall = 0x01;
        char temp;
        temp = RCREG1;     // read the incoming data
        if(temp=='$' && new_rx==0)      //if first char of a GPS string..
        {
            index = 0;                  //reset index
            reading = 1;                //from now on go to else if
        }
        else if(reading == 1)           //in middle of GPS sentence
        {
            ctxt[index] = temp;         //load it up
            index++;                    //increment index
            ping = 1;                   //this is for debugging
            if(index > 63)              //thats more than enough data
                {
                index = 0;              //reset index
                reading = 0;            //no longer storing the string
                new_rx = 1;             //"ding"
                }
        }


   }
}


/*
 * Set up my ports
 */
void init_io(void) {
    // This code before the TRIS setup is for switching the RX2/TX2 to proper pins for the dev board
    INTCONbits.GIE = 0;         //no interruptions please

    LATA = 0x00;

    TRISAbits.TRISA0 = 0; //Onboard LED
    TRISAbits.TRISA1 = 0; //LED
    TRISAbits.TRISA2 = 0; //MCU (ON)
    TRISAbits.TRISA3 = 1; // input
    TRISAbits.TRISA4 = 1; // input
    TRISAbits.TRISA5 = 1; // input
    TRISAbits.TRISA6 = 1; // input
    TRISAbits.TRISA7 = 1; // input


    TRISBbits.TRISB0 = 0; // output
    TRISBbits.TRISB1 = 0; // output
    TRISBbits.TRISB2 = 0; // PWM1B
    TRISBbits.TRISB3 = 0; // output
    TRISBbits.TRISB4 = 0; // SCK
    TRISBbits.TRISB5 = 0; // PWM1C
    TRISBbits.TRISB6 = 0; // SCK
    TRISBbits.TRISB7 = 1; // input

    LATC = 0x00;

    TRISCbits.TRISC0 = 0; // N/W
    TRISCbits.TRISC1 = 0; // S/E
    TRISCbits.TRISC2 = 0; // PWM1A (output to 4066 control)
    TRISCbits.TRISC3 = 1; // MODE SELECT (LAT/LONG)
    TRISCbits.TRISC4 = 1; // SET INPUT
    TRISCbits.TRISC5 = 1; // input
    TRISCbits.TRISC6 = 1; // input
    TRISCbits.TRISC7 = 1; // input

    ADCON0 = 0b00000000;        //don't need any ADC
    ADCON1 = 0b00000000;        //speed Vref=AVdd, VssRef=AVss

    ANSELA = 0x00;
    ANSELB = 0x00;
    ANSELC = 0x00;
}

void uart_xmit(unsigned int mydata_byte) {  //send a character to the UART
    while(!TXSTA1bits.TRMT);    // make sure buffer full bit is high before transmitting
    TXREG1 = mydata_byte;       // transmit data
}

void uart_write(const char *txt)            //sent a multiple characters
{
    while(*txt != 0) uart_xmit(*txt++);     //this send a string to the TX buffer
                                            //one character at a time
}


void serial_init(void)
{
    //9600 8N1


    TXSTA1bits.BRGH=1;       // select low speed Baud Rate
    TXSTA1bits.TX9=0;        // select 8 data bits
    TXSTA1bits.TXEN = 1;     // enable transmit


    RCSTA1bits.SPEN=1;       // serial port is enabled
    RCSTA1bits.RX9=0;        // select 8 data bits
    RCSTA1bits.CREN=1;       // receive enabled

    SPBRG1=51;  // here is calculated value of SPBRGH and SPBRGL
    SPBRGH1=0;

    PIR1bits.RCIF=0;        // make sure receive interrupt flag is clear

    __delay_ms(50);        // give time for voltage levels on board to settle
    uart_write("RESET");         // transmit some data for testing

}


void pwm_init(){
//
//Take care if setting up the PWM pins (DISBALE A/D, etc)
//
//Select the 8-bit TimerX resource, (Timer2,Timer4 or Timer6) to be used for PWM generation
//by setting the CxTSEL bits in the CCPTMRSx register.(1)
//
//Load the PRx register for the selected TimerX with the PWM period value.
//
//Configure the CCP module for the PWM mode by loading the CCPxCON register with the
//appropriate values.
//
//Load the CCPRxL register and the DCxB bits of the CCPxCON register, with the PWM
//duty cycle value.
//

//    CCPR1L = 0x120;
    CCPR1Lbits.CCPR1L = 0x01;       //PWM duty cycle
    //CCPR2Lbits.CCPR2L = 0xCE;       //PWM duty cycle
    //CCPR3Lbits.CCPR3L = 0xCE;       //PWM duty cycle
    PR2 = 0x01;                     //Timer 2 Prescale
    //PR4 = 0xFF;                     //Timer 4 Prescale
    //PR6 = 0xFF;                     //Timer 6 Prescale
    CCPTMRS0bits.C1TSEL = 0x00;     //PWM1 TMR2 Selection
    //CCPTMRS0bits.C2TSEL = 0x01;     //PWM2 TMR4 Selection
    //CCPTMRS0bits.C3TSEL = 0x02;     //PWM3 TMR6 Selection
    CCP1CONbits.P1M = 0x00;         //single output mode
    CCP1CONbits.DC1B = 0x00;
    PWM1CONbits.P1RSEN = 0;
    PWM1CONbits.P1DC = 0x00;    //dead band delay
    ECCP1ASbits.CCP1AS = 0x00;
    ECCP1ASbits.CCP1ASE = 0;    //Auto-shutdown off
    CCP1CONbits.CCP1M = 0x0C;   //PWM Mode
    //CCP2CONbits.CCP2M = 0x0C;   //PWM Mode
    //CCP3CONbits.CCP3M = 0x0C;   //PWM Mode
    PSTR1CONbits.STR1A = 1;
    PSTR1CONbits.STR1B = 1;


    //T2CONbits.T2OUTPS = 0x0F;      //post scaler
    T2CONbits.T2CKPS = 2;       //16x prescaler
    //T4CONbits.T4CKPS = 2;
    //T6CONbits.T6CKPS = 2;
    T2CONbits.TMR2ON = 1;       //Turn the Timers On...
    //T4CONbits.TMR4ON = 1;
    //T6CONbits.TMR6ON = 1;



}


/*
 *  Append a string with a character
 *  append(str, c);
 */


//taken from http://stackoverflow.com/questions/19377396/c-get-day-of-year-from-date

int yisleap(int year)
{
    return (year % 4 == 0 && year % 100 != 0);
}

int get_yday(int mon, int day, int year)
//use: int day = get_yday(1, 31, 2013);
{
    static const int days[2][13] = {
        {0, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334},
        {0, 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335}
    };
    int leap = yisleap(year);
    leapint = leap;

    return days[leap][mon] + day;
}

void append(char* s, char c)
{
        int len = strlen(s);
        s[len] = c;
        s[len+1] = '\0';
}

void marker(void){
    //send a marker frame - 800ms off, 200 ms on
    LATBbits.LATB0 = 0;
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);

    LATBbits.LATB0 = 1;
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    LATBbits.LATB0 = 0;
}

void one(void){
    //send a one - 500 ms off, 500 ms on
    LATBbits.LATB0 = 0;
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    LATBbits.LATB0 = 1;
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
}

void zero(void){
    //send a zero - 200ms off, 800ms on
    LATBbits.LATB0 = 0;
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    LATBbits.LATB0 = 1;
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
    __delay_ms(50);
}



void sendtime(void){

    /*
    *;0
    xCALL    MARKER                      ;MARKER FRAME REFERENCE BIT
    xCALL    ONE                         ;40min
    xCALL    ZERO                        ;20min
    xCALL    ZERO                        ;10min
    xCALL    ZERO                        ;Reserved
    xCALL    ZERO                        ;8mins
    xCALL    ZERO                        ;4mins
    xCALL    ONE                         ;2mins
    xCALL    ZERO                        ;1mins
    xCALL    MARKER                      ;MARKER 1
     */

    marker();                       //marker, frame reference

    if (minuteint >= 40){           //40min
        minuteint = minuteint - 40;
        one();
    }else {
        zero();
    }
    if (minuteint >= 20){           //20min
        minuteint = minuteint - 20;
        one();
    }else {
        zero();
    }
    if (minuteint >= 10){           //10min
        minuteint = minuteint - 10;
        one();
    }else {
        zero();
    }    
    zero();                        //reserved (zero)
    if (minuteint >= 8){           //8min
        minuteint = minuteint - 8;
        one();
    }else {
        zero();
    }    
    if (minuteint >= 4){           //4min
        minuteint = minuteint - 4;
        one();
    }else {
        zero();
    }    
    if (minuteint >= 2){           //2min
        minuteint = minuteint - 2;
        one();
    }else {
        zero();
    }    
    if (minuteint >= 1){           //1min
        minuteint = minuteint - 1;
        one();
    }else {
        zero();
    }    
    marker();                       //marker 1
    
    /*
    ;10
    xCALL    ZERO                        ;RESERVED
    xCALL    ZERO                        ;RESERVED
    xCALL    ZERO                        ;20hours
    CALL    ZERO                        ;10hours
    CALL    ZERO                        ;RESERVED
    CALL    ZERO                        ;8hours
    CALL    ONE                         ;4hours
    CALL    ONE                         ;2hours
    CALL    ZERO                        ;1hour
    CALL    MARKER                      ;MARKER 2     
     */
    zero();                         //reserved
    zero();                         //reserved
    if (hourint >= 20){           //20 hours
        hourint = hourint - 20;
        one();
    }else {
        zero();
    }       
    if (hourint >= 10){           //10 hours
        hourint = hourint - 10;
        one();
    }else {
        zero();
    }  
    zero();                         //reserved    
    if (hourint >= 8){           //8 hours
        hourint = hourint - 8;
        one();
    }else {
        zero();
    }  
    if (hourint >= 4){           //4 hours
        hourint = hourint - 4;
        one();
    }else {
        zero();
    }  
    if (hourint >= 2){           //2 hours
        hourint = hourint - 2;
        one();
    }else {
        zero();
    }  
    if (hourint >= 1){           //1 hours
        hourint = hourint - 1;
        one();
    }else {
        zero();
    }  
    marker();                       //marker 2    
    /*
     * 
;20
    CALL    ZERO                        ;RESERVED
    CALL    ZERO                        ;RESERVED
    CALL    ZERO                        ;200 day of year
    CALL    ONE                         ;100 day of year
    CALL    ZERO                        ;RESERVED
    CALL    ZERO                        ;80 day of year
    CALL    ONE                         ;40 day of year
    CALL    ZERO                        ;20 day of year
    CALL    ONE                         ;10 day of year
    CALL    MARKER                      ;MARKER 3
     */
    zero();                         //reserved
    zero();                         //reserved
    if (doy >= 200){           //200th day
        doy = doy - 200;
        one();
    }else {
        zero();
    }           
    if (doy >= 100){           //100th day
        doy = doy - 100;
        one();
    }else {
        zero();
    }   
    zero();                         //reserved
    if (doy >= 80){           //80th day
        doy = doy - 80;
        one();
    }else {
        zero();
    }      
    if (doy >= 40){           //40th day
        doy = doy - 40;
        one();
    }else {
        zero();
    }   
    if (doy >= 20){           //20th day
        doy = doy - 20;
        one();
    }else {
        zero();
    } 
    if (doy >= 10){           //10th day
        doy = doy - 10;
        one();
    }else {
        zero();
    }     
    marker();                       //marker 3

/*
 ;30
    CALL    ONE                         ;8 day of year
    CALL    ZERO                        ;4 day of year
    CALL    ZERO                        ;2 day of year
    CALL    ZERO                        ;1 day of year
    CALL    ZERO                        ;RESERVED
    CALL    ZERO                        ;RESERVED
    CALL    ZERO                        ;UTI Sign +
    CALL    ZERO                        ;UTI Sign -
    CALL    ZERO                        ;UTI Sign +
    CALL    MARKER                      ;MARKER 4
 */

     if (doy >= 8){           //8th day
        doy = doy - 8;
        one();
    }else {
        zero();
    }
    if (doy >= 4){           //4th day
        doy = doy - 4;
        one();
    }else {
        zero();
    }
    if (doy >= 2){           //2nd day
        doy = doy - 2;
        one();
    }else {
        zero();
    }
    if (doy >= 1){           //1st day
        doy = doy - 1;
        one();
    }else {
        zero();
    }
    zero();                         //reserved
    zero();                         //reserved
    zero();                         //reserved
    zero();                         //reserved
    zero();                         //reserved
    marker();                       //marker 4

    /*
   ;40
    CALL    ZERO                        ;UTI Corr 0.8s
    CALL    ZERO                        ;UTI Corr 0.4s
    CALL    ZERO                        ;UTI Corr 0.2s
    CALL    ZERO                        ;UTI Corr 0.1s
    CALL    ZERO                        ;RESERVED
    CALL    ZERO                        ;80 year yearint
    CALL    ZERO                        ;40 year
    CALL    ZERO                        ;20 year
    CALL    ONE                         ;10 year
    CALL    MARKER                      ;MARKER 5
     */

    zero();                         //reserved
    zero();                         //reserved
    zero();                         //reserved
    zero();                         //reserved
    zero();                         //reserved

    if (yearint >= 80){           //80th year
        yearint = yearint - 80;
        one();
    }else {
        zero();
    }
    if (yearint >= 40){           //40th year
        yearint = yearint - 40;
        one();
    }else {
        zero();
    }
    if (yearint >= 20){           //20th year
        yearint = yearint - 20;
        one();
    }else {
        zero();
    }
    if (yearint >= 10){           //10th year
        yearint = yearint - 10;
        one();
    }else {
        zero();
    }
    marker();                       //marker 5

/*
     *
;50
    CALL    ZERO                        ;8 year
    CALL    ONE                         ;4 year
    CALL    ONE                         ;2 year
    CALL    ZERO                        ;1 year
    CALL    ZERO                        ;RESERVED
    CALL    ZERO                        ;LEAP YEAR TRUE
    CALL    ZERO                        ;LEAP SEC WARN
    CALL    ONE                        ;DST
    CALL    ONE                        ;DST
    CALL    MARKER                        ;FRAME BIT P0
    *
*/

    if (yearint >= 8){           //8th year
        yearint = yearint - 8;
        one();
    }else {
        zero();
    }
    if (yearint >= 4){           //4th day
        yearint = yearint - 4;
        one();
    }else {
        zero();
    }
    if (yearint >= 2){           //2nd day
        yearint = yearint - 2;
        one();
    }else {
        zero();
    }
    if (yearint >= 1){           //1st day
        yearint = yearint - 1;
        one();
    }else {
        zero();
    }
    zero();                         //reserved

                                     //leap year
    if (leapint){
        one();
    }else {
        zero();
    }
    zero();
    zero();                         //leap sec warn
    zero();                         //dst??
    zero();                         //dst
    marker();                       //frame bit P0
}

void gettime(void){
    
    hourch[0] = wstr[6];      //HHMMSS
    hourch[1] = wstr[7];

    minch[0] = wstr[8];
    minch[1] = wstr[9];

    secch[0] = wstr[10];
    secch[1] = wstr[11];

    daych[0] = wstr[56];     //DAY1  DDMMYY
    daych[1] = wstr[57];     //DAY2

    monthch[0] = wstr[58];     //MONTH1
    monthch[1] = wstr[59];     //MONTH2

    yearch[0] = wstr[60];     //YEAR1
    yearch[1] = wstr[61];     //YEAR2

    uart_write(wstr);

    uart_write(" ");

   hourint = atoi(hourch);
   minuteint = atoi(minch);
   secondint= atoi(secch);

   dayint = atoi(daych);
   monthint = atoi(monthch);
   yearint = atoi(yearch);

   year4int = yearint + 2000;

   doy = get_yday(monthint, dayint, yearint);

   ltoa(doych,doy,10);

   uart_write(doych);

    uart_write("\r");
}

void lon(void){

}

void determine_mode(void){  //determine lat or long mode

}


int main(void) {

    // set up oscillator control register, using internal OSC at 8MHz.
    OSCCONbits.IRCF = 0x06; //set OSCCON IRCF bits to select OSC frequency 8MHz
    OSCCONbits.SCS = 0x02; //set the SCS bits to select internal oscillator block
    __delay_ms(70);         //lets think about life a bit before proceeding..
    __delay_ms(70);
    __delay_ms(70);

    ping = 0;
    new_rx = 0;
    isrcall = 0;

    init_io();
    serial_init();

    //RCONbits.IPEN = 0;
    PIE1bits.RC1IE = 1;         //Enable RX Interrupt
    INTCONbits.PEIE = 1;        // Enable peripheral interrupt
    INTCONbits.GIE = 1;         // enable global interrupt

    pwm_init();

    ready = 0;

    while (1) {
    __delay_ms(10);
    isrcall = 0;
    ping = 0;
    if (ready){
        LATCbits.LATC2 = 1;
    }

        if (new_rx == 1)            //got our string...
        {
            if (strstr(ctxt, "GPRMC"))  // && ready
            {
                gprmc = 1;
                strncpy((char*)wstr, (char*)ctxt, sizeof(ctxt));
                gettime();
            }
            new_rx=0;              //finished with GPS string
        }


    if (gprmc){
        sendtime();
    }
    gpgga = 0;
    gprmc = 0;
    }
}
C Electronics GPS Microcontrollers PIC

GPS on the PIC 18F26K22

I was asked to create a box that notified by LED if you were too far off a N/S or E/W course. I failed, I doubted the specified GPS accuracy/drift as my Garmin seems to stay pretty steady.. perhaps that’s some integration in the processing?

I started with one of the 18F26K22 TAUTIC development boards I bought from him off Tindie; They’re nice little breadboarding microcontrollers… I’ve recommended them before. I had purchased some GPS modules I got from eBay, so check .. they all have TTL NMEA output, some with 1PPS… and finally some tidbits I picked up out of my parts collection. Wrote some code.. tested it and found my drifting issue. After pondering the number 42 a while, I decided there was no sense in continuing because every idea I had meant something in the specification of the project was out.

I’m not going to go deep into explanation of the code since the project didn’t work but like all failures I learned something. I also expanded my knowledge of XC8 which was nice..  I’ve actively been coding in XC8 for a few months now; in some ways I miss ASM but XC8 does shorten the development time (if you don’t count how long it takes me to figure out atol() should have been used instead of atoi().

This project will be converted into a piece of test equipment of sorts. I’ve been meaning to hook a GPS receiver up to my WWVB transmitter and check it out. Of course WWVB is way more accurate … but if you can’t receive WWVB .. you’re up a creek.

 

GPS Receiver and Microcontroller outside locked.
GPS Receiver and Microcontroller outside locked.

Keep in mind this code is un-optimized, and essentially abandoned while I was building the framework. I leave it to you in case you want a jump start on grabbing some data out of a NMEA string.

/*
/*
 * File:   main.c
 * Author: Charles M Douvier
 * Contact at: http://iradan.com / 0xEE.net / @chasxmd
 * Created on April 4th, 2014
 *
 * Target Device: TAUTIC.com dev board / 18F26K22
 *
 * Project: AG GPS Indicator
 * Using a PIC to indicate if you're staying in lat/long "groove" by GPS.
 * *** This is not complete ***
 *
 *
 * Version:
 * 0.1      First build I could prove I had GPS lock
 * 0.2      Output GPS on 232 and position set, no debounce, etc.. abandonded
 */
#ifndef _XTAL_FREQ
#define _XTAL_FREQ 4000000 //4Mhz FRC internal osc
#define __delay_us(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000000.0)))
#define __delay_ms(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000.0)))
#endif

#include 
#include 
#include 
#include 


//config bits
#pragma config FOSC=INTIO67, WDTEN=OFF, PWRTEN=OFF, CP0=OFF, CP1=OFF, BOREN=ON
#pragma config STVREN=ON, LVP=OFF, HFOFST=OFF, IESO=OFF, FCMEN=OFF

//WRT=OFF, FOSC=INTOSC, MCLRE=ON

#define _XTAL_FREQ 4000000 //defined for delay

    char    ctxt[120], wstr[120];            //buff NMEA string, working string
    char    str[60], c, latstr, lonstr, setstr;
    char buffer[32] = "none";                        //temp dump
    volatile unsigned int     ping, isrcall, index, reading, new_rx;
    int     ready, gpgga, gprmc, mode;        //gps associated vars
    long long    position_set, position_now;
    //char    *rxdata;
    //volatile unsigned int uart_data;    // use 'volatile' qualifer as this is changed in ISR

/*
 *  Interrupt Service
 */
void interrupt ISR() {

   if (PIR1bits.RCIF){          // see if interrupt caused by incoming data

        isrcall = 0x01;
        char temp;
        temp = RCREG1;     // read the incoming data
        if(temp=='$' && new_rx==0)      //if first char of a GPS string..
        {
            index = 0;                  //reset index
            reading = 1;                //from now on go to else if
        }
        else if(reading == 1)           //in middle of GPS sentence
        {
            ctxt[index] = temp;         //load it up
            index++;                    //increment index
            ping = 1;                   //this is for debugging
            if(index > 50)              //thats more than enough data
                {
                index = 0;              //reset index
                reading = 0;            //no longer storing the string
                new_rx = 1;             //"ding"
                }
        }


   }
}


/*
 * Set up my ports
 */
void init_io(void) {

    INTCONbits.GIE = 0;         //no interruptions please

    LATA = 0x00;

    TRISAbits.TRISA0 = 0; //Onboard LED
    TRISAbits.TRISA1 = 0; //LED
    TRISAbits.TRISA2 = 0; //MCU (ON)
    TRISAbits.TRISA3 = 1; // input
    TRISAbits.TRISA4 = 1; // input
    TRISAbits.TRISA5 = 1; // input
    TRISAbits.TRISA6 = 1; // input
    TRISAbits.TRISA7 = 1; // input


    TRISBbits.TRISB0 = 0; // output
    TRISBbits.TRISB1 = 0; // output
    TRISBbits.TRISB2 = 0; // output
    TRISBbits.TRISB3 = 0; // output
    TRISBbits.TRISB4 = 0; // SCK
    TRISBbits.TRISB5 = 1; // input
    TRISBbits.TRISB6 = 0; // SCK
    TRISBbits.TRISB7 = 1; // input

    LATC = 0x00;

    TRISCbits.TRISC0 = 0; // N/W
    TRISCbits.TRISC1 = 0; // S/E
    TRISCbits.TRISC2 = 0; // GPGGA DETECT
    TRISCbits.TRISC3 = 1; // MODE SELECT (LAT/LONG)
    TRISCbits.TRISC4 = 1; // SET INPUT
    TRISCbits.TRISC5 = 1; // input
    TRISCbits.TRISC6 = 1; // input
    TRISCbits.TRISC7 = 1; // input
    
    ADCON0 = 0b00000000;        //don't need any ADC
    ADCON1 = 0b00000000;        //speed Vref=AVdd, VssRef=AVss

    ANSELA = 0x00;
    ANSELB = 0x00;
    ANSELC = 0x00;
}

void uart_xmit(unsigned int mydata_byte) {  //send a character to the UART
    while(!TXSTA1bits.TRMT);    // make sure buffer full bit is high before transmitting
    TXREG1 = mydata_byte;       // transmit data
}

void uart_write(const char *txt)            //sent a multiple characters
{
    while(*txt != 0) uart_xmit(*txt++);     //this send a string to the TX buffer
                                            //one character at a time
}


void serial_init(void)
{
    //9600 8N1

    
    TXSTA1bits.BRGH=1;       // select low speed Baud Rate 
    TXSTA1bits.TX9=0;        // select 8 data bits
    TXSTA1bits.TXEN = 1;     // enable transmit


    RCSTA1bits.SPEN=1;       // serial port is enabled
    RCSTA1bits.RX9=0;        // select 8 data bits
    RCSTA1bits.CREN=1;       // receive enabled

    SPBRG1=25;  // here is calculated value of SPBRGH and SPBRGL
    SPBRGH1=0;

    PIR1bits.RCIF=0;        // make sure receive interrupt flag is clear

    __delay_ms(50);        // give time for voltage levels on board to settle
    uart_write("RESET");         // transmit some data for testing

}


/*
 *  Append a string with a character
 *  append(str, c);
 */


void append(char* s, char c)
{
        int len = strlen(s);
        s[len] = c;
        s[len+1] = '\0';
}



/*
 *
 * convert the decminal bits of lat or long to integer
 * send over RS-232 for review
 *
 *
 */



void lat(void){
    str[0] = wstr[17];
    str[1] = wstr[18];
    str[2] = wstr[19];
    str[3] = wstr[20];   // .21 is a decimal place
    str[4] = wstr[22];
    str[5] = wstr[23];
    str[6] = wstr[24];
    str[7] = wstr[25];

    position_now = atol(str);

    uart_write(str);
    uart_write(" ");

        //check to set position
    if (PORTCbits.RC4 && ready) {
        position_set = position_now;
    }

    if (position_set){
        if (position_now > (position_set + 3)) {
            LATCbits.LATC1 = 1;
        }   else {
            LATCbits.LATC1 = 0;
        }
        
        if (position_now < (position_set - 3)) {
            LATCbits.LATC0 = 1;
        }   else {
            LATCbits.LATC0 = 0;
        }
    }
        sprintf(buffer, "%lld", position_now);
        uart_write(buffer);
        uart_write(" ");
        sprintf(buffer, "%lld", position_set);
        uart_write(buffer);
    uart_write("\r");
}

void lon(void){
 //not started
}

void determine_mode(void){  //determine lat or long mode
 //not started   
}


int main(void) {

    // set up oscillator control register, using internal OSC at 4MHz.
    OSCCONbits.IRCF = 0x05; //set OSCCON IRCF bits to select OSC frequency 4MHz
    OSCCONbits.SCS = 0x02; //set the SCS bits to select internal oscillator block
    __delay_ms(50);         //lets think about life a bit before proceeding..


    ping = 0;
    new_rx = 0;
    isrcall = 0;
    
    init_io();
    serial_init();

    //RCONbits.IPEN = 0;
    PIE1bits.RC1IE = 1;         //Enable RX Interrupt
    INTCONbits.PEIE = 1;        // Enable peripheral interrupt
    INTCONbits.GIE = 1;         // enable global interrupt

    
    ready = 0;

    while (1) {
    isrcall = 0;
    ping = 0;
    if (ready){
        LATCbits.LATC2 = 1;
    }

    LATAbits.LATA2 = 1;         //startup heartbeat LED
    __delay_ms(1);
    LATAbits.LATA2 = 0;

        if (new_rx == 1)            //got our string...
        {
            if (strstr(ctxt, "GPGGA"))
            {
                gpgga = 1;
                strncpy((char*)wstr, (char*)ctxt, sizeof(ctxt));  
            }
            new_rx=0;              //finished with GPS string
        }

        if (gpgga) {
            LATAbits.LA1 = 0;
            if(ctxt[42] == '1')     //this is the 43rd bit but we didn't drop the $ into the buffer
            {                       //If "$GPGGA" NMEA message has '1' sign in the 43rd
                                    //position it means that tha GPS receiver has a position fix
                                    //
            ready = 1;              //This is my "locked" variable for future code
            LATAbits.LATA1 = 1;     //LOCK LED
            }
        }

    if (ready) {

        if (mode){

        }
        if (!mode) {
            lat();
        }
        
    }
    __delay_ms(149); //delay don't really even need to update this often
    }
}

If you noticed my posts/week is way down.. well it’s summer. This will happen every summer. My daughter is home and so my time gets happily gobbled up by her :) I’ve got a huge backlog of projects.. thankfully the day job has eased off a bunch. I’m working on a 0xEE project which I probably should have been doing today.. but I needed a break. Also I recently found out our annual backpacking trip is going to be a bit more intense; I’ll have to train appropriately .. so less time on the bench. It’ll be this way until September I imagine.

C Electronics Interface RS-485

TIA-485 PIC tutorial

I just finished up a basic tutorial of using TIA-485 (RS-485/EIA-485) with a PIC micro on 0xEE.net.. this will be part one of at least 2 or 3 articles.

 

 0xEE.net PIC Talks RS-485

Electronics

First Hexacopter Flight

Wow, an action packaged summer so far… no much bench-time unfortunately but work has let off and I’m working sub-50 hour weeks again thankfully.  I did get to spend some time this weekend on the bench but really not much. I worked on an article for 0xEE.net and a little fixing for the wife. I did grab my F550 for its first flight (and mine on something larger than one of those micro-quads as well!). I had no intention of filming this… but my wife ended up taking a poor quality video off a cheapo-camera not meant for it. I’m glad she did.. :) I had a visitor.. some dog being walked couple decided to take an interest in the loud flying thing in the air.. it was a little nerve-racking because I didn’t want any accidents but luckily zero problems and no crashing! I can see the appeal of FPV .. it’s a little hard to determine pitch when they get out a bit. I think I’ll have to invest in something like that.

So here is the grainy video of some dog enjoying his day..

Natalie also took an interest in refreshing her soldering skills and was bragging to her uncle she had been soldering since she was four and was better at it than him… I had her soldering one of the waveform generators I made a PCB for without the proper silkscreen.. good times.

IMG_4776

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