我基于Si5351a模塊制作了VFO。為了提高頻率的精度，我借助了GPS PPS信號。

Si5351a是制作精確時鐘的好芯片。但由于其晶體振蕩器電路的原因，存在一定的頻率誤差。將其頻率與GPS PPS進行比較，可以得到兩者之差的校正值。該頻率校正值可用于VFO校正。

原理圖

代碼

// 2025.01.07 pps OK, Sw1.2 OK 91%/62%

// 2024.12.09 tiny4kOLED

// 2024.11.16 Refered and Changed for R909-VFO-GPS

// added correction FREQ display

// changed store condition correction

// GITHUB https://github.com/Nobcha/R909-VFO-GPS

// D2:PPS,D5:2.5M,D7:EN,D0/RX:GPS/TX,LCD1602

//

// gps-calibration-5351

//　https://github.com/csqwdy/gps-calibration-5351/blob/main/README.md

// 2022-03-06 Modified the encoder to work in signal change interrupt mode,

// Original was SQ1GU http://sq1gu.tobis.com.pl/en/dds

// include the library code:

#include <TINYGPS++.H>

// Change to OLED

#include

#include

#include

#include

#include

#include

#include

// The TinyGPS++ object

TinyGPSPlus gps;

Si5351 si5351;

#define control 2 // 1=button ,2=EP11 ,3=EP12

// Set up MCU pins

#define GPS_Enable 7

#define ppsPin 2 // GPS-PPS INT

#define re_sw A0

#define encoderPinA 4 // Signal change INT

#define encoderPinB 3 //

#define ledPin A1

#define func_sw A2 // SW1:<80, SW2:<250,

#define Freq2 1000000000ULL

volatile byte seqA = 0;

volatile byte seqB = 0;

volatile byte cnt1 = 0;

volatile byte cnt2 = 0;

volatile boolean right = false;

volatile boolean left = false;

volatile boolean button = false;

// configure variables

unsigned long XtalFreq = 100000000;

unsigned long XtalFreq_old = 100000000;

long stab;

long correction = 0;

byte stab_count = 44;

unsigned long mult = 0, Freq = 10000000;

int second = 0, minute = 0, hour = 0;

int zone = 9;

unsigned int tcount = 0;

unsigned int tcount2 = 0;

int validGPSflag = false;

char c;

boolean newdata = false;

boolean GPSstatus = true;

byte new_freq = 1;

unsigned long freq_step = 1000;

byte encoderOLD, menu = 6, band = 1, f_step = 1;

boolean time_enable = true;

unsigned long pps_correct_time;

byte pps_valid = 0;

byte correct_byte = 1;

float stab_float;

unsigned long button_on_time;

boolean oled_turn = 1;

boolean vfo_counter = true; // true vfo

boolean new_c_freq = 0;

boolean pps_error = 1;

int func_sw_value;

// prototype

void PPSinterrupt(void);

void timezone_on_oled(void);

void stab_on_oled(void);

void correct_freq(void);

void corr_on_oled(void);

void freq2_on_oled(void);

void step_on_oled(void);

void band_on_oled(void);

void time_on_oled(void);

void sat_on_oled(void);

void freq_on_oled(unsigned long);

void update_si5351a(void);

void correct_si5351a(void);

static void GPSproces(unsigned long);

void change_up(void);

void change_down(void);

void loglat_on_oled(void);

void vfo_fr_oled (void);

void date_on_oled(void);

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

// Timer 1 overflow intrrupt vector. Count 2.5MHz

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

ISR(TIMER1_OVF_vect)

{

mult++; //Increment multiplier

TIFR1 = (1 << TOV1); //Clear overlow flag

}

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

// Judge the rotating direction

// Signal change interrupt

本文編譯自hackster.io