Introduction
This circuit is a repeater for GPS data. It is intended to connect to Garmin-38 (and similar) hand held GPS receivers that don’t have external antennas. The purpose for the repeater is to allow the GPS to be outside, exposed to the satellite view, and allow the user to see the data below decks at the navigation station.
Versions
Within the code there is opportunity to easily configure for a 16×4 display or a 20×4 display, as well as configure it for crystal speeds from 4 to 20MHz, and for nautical, metric, or statute speed display. Although the description below is for the 16×4 version, the 20×4 is quite similar.
Herb Young in Australia built a very nice boxed version of the repeater.
Features
The repeater displays several pages of data pertaining to both the GPS and the boat electrical system. A DB-9 jack is on the front panel for the purposes of connection of a laptop to upload and download GPS waypoint data, etc. This code is a good example of how to process serial data using the PIC16F87x hardware UART and the serial interrupt.
Specifications
- Power: 10-16VDC at ~150mA including GPS
- Analog: three inputs, 14.99VDC maximum displayed value
- Data: NMEA-0183 2.0 format (4800 baud, TTL level, RMB & RMC data sentences)
Operation
Apply power to the repeater. The following screen is displayed
- The three buttons cycle through the three pages, which are:
- Position (Latitude – Longitude – Speed – Heading)
- Waypoint (Waypoint name – Steering – Distance – Bearing)
- Battery voltages
- Pressing and holding the Position button for between one and three seconds toggles the background illumination on and off.
- Pressing and holding the Position button for four or more seconds resets the microprocessor (like power-on-reset.)
- Pressing and holding the Position button during power-up will display the Setup Page, described below.
Code:
// Change the following to change the clock frequency #define CRYSTAL_FREQ 16000000 // Change the following to change between 16 or 20 column display #define DISPLAY_COLS 20 // Speed units are "1" (nautical knots), "2" (metric kph), or "3" (statute mph) #define SPEED_UNITS 1 /**************************************************************************** GPS18.c This program receives NMEA-0183 data from a GPS and displays it. Meant for large display version still in 16F876. Three buttons Automicaly resets if main loop stops (not the best solution, still don't know why it's stopping) Next: don't display GPS screens unless GPS is active detect display needing reset preset data eeprom for first-time operation don't display init stuff if reseting from main loop +5 +5+5 | | | 20 15 2 ---------- ---------- ~SerIn -----18-| |-24-----11-|DB4 A Vdd | | |-25-----12-|DB5 | ADC0 ------2-| |-26-----13-|DB6 | ADC1 ------3-| 16F876 |-27-----14-|DB7 Vo| 3-- ADC2 ------5-| | | LCD | | | |-14------6-|EN | | XTAL--9-| |-15------4-|R/S | | XTAL-10-| |-28-FET-16-|K | | | | | RW Vss | | BUTTON 1---21-| | ---------- | BUTTON 2---22-| | 1 5 | BUTTON 3---23-| | | | | | | Gnd Gnd | | | | | |-11----------R/C----------- | | | | ---------- 8 19 | | Gnd Gnd ***************************************************************************/ #case #include < 16F876.h > #include < jonsinc.h > #device = *=16 ADC=10 /* allow RAM addresses over 255 */ #if ( ( CRYSTAL_FREQ < 4000000) || ( CRYSTAL_FREQ > 20000000 ) ) #error "CRYSTAL FREQ" not defined to between 8000000 and 20000000 #endif #if ( ( DISPLAY_COLS != 16 ) && ( DISPLAY_COLS != 20 ) ) #error "DISPLAY COLS" not defined to 16 or 20 #endif // RMC_TIME = 1 per clock megahertz, rounded #define RMC_TIME CRYSTAL_FREQ/1000000 #define LCD_D0 PIN_B3 #define LCD_D1 PIN_B4 #define LCD_D2 PIN_B5 #define LCD_D3 PIN_B6 #define LCD_EN PIN_C3 #define LCD_RS PIN_C4 #define RX_IN PIN_C7 #define BUTTON_1 PIN_B0 #define BUTTON_2 PIN_B1 #define BUTTON_3 PIN_B2 #define LCD_BACKLITE PIN_B7 #define LINE_1 0x00 #define LINE_2 0x40 #if DISPLAY_COLS == 20 #define LINE_3 0x14 #define LINE_4 0x54 #endif #if DISPLAY_COLS == 16 #define LINE_3 0x10 #define LINE_4 0x50 #endif #define CLEAR_DISP 0x01 #define EOF 0x00 #define COMMA ',' #define CR 13 #define SPACE ' ' #define PERIOD '.' #define DEGREE 0xdf #define DOLLAR '$' #define NULL 0 #define GPRMC_CODE 75 #define GPRMB_CODE 74 #define RX_BUFFER_SIZE 70 #define POSITION_SCREEN 1 #define WAYPOINT_SCREEN 2 #define BATTERY_SCREEN 3 #define HIDDEN_RMC 5 #define WARNING_MSG 0 #define NODATA_MSG 1 #define ACTIVITY_SYMBOL 0xFF #define MAX_VOLTS 15 #define EEPROM_CONTRAST 0 #define EEPROM_INITIAL 1 /* Set the following define to "YES" to display XOR'ed GPS sentence code */ /* such as GPRMC and the display will read out the value of 74. */ #define GET_GPS_CODE NO #separate void Display ( void ); #separate void LCD_Init ( void ); #separate void LCD_SetPosition ( unsigned int cX ); #separate void LCD_PutChar ( unsigned int cX ); #separate void LCD_PutCmd ( unsigned int cX ); #separate void LCD_PulseEnable ( void ); #separate void LCD_SetData ( unsigned int cX ); #separate void SkipField ( char cCnt ); #separate char GetField ( void ); #separate void InitRxBuffer ( char cCode ); #separate char GetRxChar ( void ); #separate void DisplayLatLon ( void ); #separate void DisplayWaypoint ( void ); #separate void DisplayLatitude ( char cLine ); #separate void DisplayLongitude ( char cLine ); #separate void DisplayHeading ( char cLine ); #separate void DisplaySpeed ( char cLine ); #separate void DisplaySteer ( char cLine, char cX ); #separate void DisplayWaypointName ( char cLine, char cX ); #separate void DisplayDistance ( char cLine, char cX ); #separate void DisplayBearing ( char cLine, char cX ); #separate void GetUtcAndMagVar ( void ); #separate long TrueToMag ( long iH ); #separate long FieldFiveToLong ( void ); #separate void DisplayAnalog ( void ); #separate void DisplayScaledVoltage ( long iV, char cScale ); #separate void DisplayArrival ( char cLine ); #separate void DisplayMessage ( char cMsgNum ); #separate void DisplayTemplateLatLon ( void ); #separate void DisplayTemplateWaypoint ( void ); #separate void DisplayTemplateAnalog ( void ); #separate void Delay5mS ( char cCnt ); #fuses HS, NOPROTECT, PUT, NOWDT, BROWNOUT, NOLVP, NOCPD #use standard_io ( A ) #use standard_io ( B ) #use standard_io ( C ) #use delay ( clock = CRYSTAL_FREQ ) #use rs232 ( baud=4800, xmit=PIN_C6, rcv=PIN_C7, ERRORS ) // XMIT must be assigned to enable hardward USART #priority RDA, RTCC, EXT static char cC [ 10 ]; // local buffer static char cTimeOut; static char cRxBuffer [ RX_BUFFER_SIZE ]; // Fifo static char cRxByteCnt; // Number of bytes in the recv fifo static char *cRxBufferWritePtr; // Pointers for the Rx buffer static char *cRxBufferReadPtr; static char cRxIsrState, cRxMsgTypeReceived, cRxMsgTypeDesired; static char cRxMsgReady, cReceiveFlag; static long iVar, iLastRange, iTimeOut; static char cVarDir, cScreenChanged, cAdcDone; static char cButtonPressed, cSkip, cButtonCount; static char cScreen, cSavedScreen, cRmcTimer1, cRmcTimer2; static char cToFrom [ 5 ], cIndicator, cIllumination, cRxErrorFlag; static char cDone, cContrast; /*******************************************************************/ #int_ad void AdcInterrupt ( void ) { /* Gets here when ADC is done conversion, sets flag */ cAdcDone = YES; } #int_timer1 void Timer1Interrupt ( void ) { /* Periodic RMC data timer, gets here every 204mS */ /* This routine forces RMC to run every 10 minutes to update */ /* magnetic variation */ if ( cRmcTimer1-- == 0 ) { cRmcTimer1 = 255; // 52 seconds @ 10.240MHz if ( cRmcTimer2-- == 0 ) { cRmcTimer2 = RMC_TIME; // triggers every 10 minutes cSavedScreen = cScreen; // save current screen type cScreen = HIDDEN_RMC; // force RMC to run } } } #int_rtcc void Timer0Interrupt ( void ) { // Gets here every 16.4mS at 8MHz, 8.2mS at 16MHz // Handles data timeout and switch debounce. // DATA TIMEOUT TIMER if ( cTimeOut != 0 ) { cTimeOut--; } // This timer is preset by the normal operating loop, unless the operating // loop stops looping, at which point iTimeOut finally decrements to zero // and resets CPU. if ( iTimeOut != 0 ) { iTimeOut--; } else { reset_cpu(); // force reset } if ( input ( BUTTON_2 ) == LOW ) // if button still pressed { cScreen = WAYPOINT_SCREEN; cSkip = YES; // skip out of anything in process cScreenChanged = YES; // repaint complete screen } if ( input ( BUTTON_3 ) == LOW ) // if button still pressed { cScreen = BATTERY_SCREEN; cSkip = YES; // skip out of anything in process cScreenChanged = YES; // repaint complete screen } // SWITCH DEBOUNCE if ( input ( BUTTON_1 ) == LOW ) // if button still pressed { if ( cButtonCount < 255 ) // hold at 255 { cButtonCount++; // otherwise increment } } else // if button is unpressed { if ( cButtonCount > 2 ) // filter out glitches { //If button press is greater than 3.3 seconds, cold reset if ( cButtonCount == 255 ) { reset_cpu(); } if ( ( cButtonCount > 57 ) && ( cButtonCount < 255 ) ) { if ( cScreen != HIDDEN_RMC ) // if not in the middle of getting magnetic variation { // cIllumination ^= ON; output_bit ( LCD_BACKLITE, cIllumination ^= ON ); } } // If button press is less than 0.5 second if ( cButtonCount <= 57 ) { if ( cScreen != HIDDEN_RMC ) // if not in the middle of getting magnetic variation { //if ( cScreen++ >= BATTERY_SCREEN ) // increment to next screen { cScreen = POSITION_SCREEN; // wrap } cSkip = YES; // skip out of anything in process cScreenChanged = YES; // repaint complete screen } } } cButtonCount = 0; // restart } } #int_rda void SerialInterrupt ( void ) { /* Reads incoming data from the USART and puts in in a rolling buffer ( but in this application, it should never roll.) If the buffer is full, this routine just discards the received byte. Not checking the LRC byte at the end of the NMEA-0183 sentence. */ char cChar; if ( rs232_errors & 0x04 ) // get framing error bit from Rx status reg { cRxErrorFlag = ON; } cChar = getchar(); // get char from UART, clear any errors if ( cRxByteCnt == RX_BUFFER_SIZE ) // is recv fifo full ??? { goto done; } switch ( cRxIsrState ) { case 0: { if ( cChar == DOLLAR ) // if start of NMEA0183 message { cRxByteCnt = 0; // reset byte count cReceiveFlag = OFF; // default to off cRxMsgTypeReceived = NULL; // set hashed value to null cRxIsrState++; // next state } break; } case 1: // five type characters to obtain case 2: case 3: case 4: case 5: { cRxMsgTypeReceived ^= cChar; // hash in msg type if ( cRxIsrState++ == 5 ) // if time to check message type { if ( cRxMsgTypeReceived == cRxMsgTypeDesired ) // if good { cReceiveFlag = YES; // enable receiving cRxBufferWritePtr = cRxBuffer; // reset to beginning of buffer } else // don't want this message { cRxIsrState = 0; // reset to look for next msg } } break; } case 6: { /* Case 6 skips the comma character following msg type */ cRxIsrState++; break; } default: // remainder of characters { if ( cReceiveFlag == YES ) // if this message is wanted { *cRxBufferWritePtr = cChar; // put char in fifo cRxBufferWritePtr++; // increment pointer if ( cRxBufferWritePtr == ( cRxBuffer + RX_BUFFER_SIZE ) ) // pointer past end ? { cRxBufferWritePtr = cRxBuffer; // set pointer to start of fifo } cRxByteCnt++; // Increment byte count if ( cChar == CR ) { cRxMsgReady = YES; // signal that message is ready cReceiveFlag = NO; // no more receive } } } } done:; } /*******************************************************************/
For more detail: GPS REPEATER/SYSTEMS MONITOR using PIC16F876