Arduino/Genuino STANDARDMOD

An instructive 10 MHz OCXO Shield

✈ The used Quartz Crystal

✈ Circuit Description

✈ The Oscillator • NB3N502 from ON Semiconductor

NB3N502 Block Diagram, Drawing courtesy of ON Semiconductor

This Oscillator was chosen, because it is a useful device and yes, because it was in our treasure-box. It allows the easy generation of almost any carrier without any programming. We did some investigation earlier on this circuit here.

"The NB3N502 is a clock multiplier device that generates a low jitter, TTL/CMOS level output clock which is a precise multiple of the external input reference clock signal source. You can use any crystal in the range of 5 − 27 MHz". The PLL can easily be configured by just two pins. The table below shows the clock multiplying settings. And yes, for an OCXO you should use only NP0 Capacitors.

NB3N502 Clock Multiplying Settings, Table courtesy of ON Semiconductor

✈ Stability • Accuracy • Long Term Stability • Allan Deviation

The design is based on a circuit designed by my colleague, Dipl. Ing. Peter Märki. You mayst find details on the heating circuit on the NCCR "QSIT - Quantum Science and Technology" website.

What is this Ageing stuff anyhow ?

In terms of electronic circuits, this means that one or more parameters change slowly with age. For a crystal oscillator, this means, that the frequency changes with time when external factors to the oscillator such as environment and power supply are kept constant. Ususally the frequency will rise.

What is this Allan Deviation ?

This is the standard method of characterizing the frequency stability of oscillators in the time domain, both short and long term. The following test-setup was used. Results to be seen in the "Performance" section.

If you want to set up such a test-bench, choose a counter with a small resolution. See the influence here. Target is in the 1... 10 Picosecond range. The lower, the b€tter :-)

✈ Test Sketch for Arduino/Genuino UNO

/* ///////////////////////////////////////////////////////////////////// 
ARDUINO/Genuino (MEGA2560) Sketch for "OCXO 10 MHz"
https://www.changpuak.ch/electronics/Arduino-Shield-STANDARDMOD.php
Software Version 1.9, 
23.07.2019, Alexander Sse Frank, 
//////////////////////////////////////////////////////////////////////*/

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SH1106.h>
#include "AD9835.h"

AD9835 dds(
        3, // FSYNC
        5, // SCLK
        4, // SDATA
        2, // FSEL, NO HAVE
        A2, // PSEL1, NO HAVE
        A1, // PSEL0, NO HAVE
        40000000 // MasterClockFrequency
    );

float SetPointTemp = 75.0 ;         // TEMPERATURE
unsigned int SetPointDAC = 48510  ; // INTEGER  
float CurrentTemp = 0.0 ;

float HeatPower = 0.0 ;
float HeatPowerVolt = 0.0 ;
boolean Reliable = false ;

int BEEPER = A2 ;
int BUTTON = A3 ;
int HeatPowerPin = A0 ;
int TMP101 = 0x4A ;

int DAC8571 = 0x4C ;

unsigned long XTAL = 10000000 ;   // THE QUARTZ IN USE
unsigned long NB3N502_MULTI = 4 ; // AS SELECTED BY J2 (S1) AND J3 (S0)
unsigned long DDS_CLOCK = NB3N502_MULTI * XTAL ;  // 40 MHz
unsigned long FREQ = 9997428 ;    // DESIRED REFERENCE CLOCK
unsigned long REF_MUL = 0x0000 ;  // WE DON'T USE THIS
 


// OLED 128x64 with SH1106 Controller
// E.G. DM-OLED13-625
#define OLED_MOSI  9
#define OLED_CLK   8
#define OLED_DC    11
#define OLED_CS    12
#define OLED_RESET 10
Adafruit_SH1106 display(OLED_MOSI, OLED_CLK, OLED_DC, OLED_RESET, OLED_CS);

#if (SH1106_LCDHEIGHT != 64)
#error("Height incorrect, please fix Adafruit_SH1106.h!");
#endif


void setup() 
{
  delay(999);
  pinMode(BEEPER, OUTPUT);
  digitalWrite(BEEPER, LOW); 
  pinMode(BUTTON, INPUT_PULLUP);

  // DEFINE INPUT
  pinMode (HeatPowerPin, INPUT_PULLUP);
  // INIT OLED
  display.begin(SH1106_SWITCHCAPVCC);
  // SHOW STARTUP SCREEN
  display.clearDisplay();
  display.drawLine(0, 14, 128, 14, WHITE);
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0,0);
  display.println("**** STANDARDMOD ****");
  display.setTextSize(1);
  display.setCursor(0,21);
  display.println("A 10 MHz OCXO");
  display.setCursor(0,33);
  display.println("BASED ON THE AD9835");
  display.setCursor(0,45);
  display.println("(C) ETH QUANTUMOPTICS");
  display.setCursor(0,57);
  display.println("BUILT 24.07.2019");
  display.display();
  
  delay(9999);
  
  // POST #1 -----------------------------------------------------------
  digitalWrite(BEEPER, HIGH); 
  delay(1999);
  digitalWrite(BEEPER, LOW); 
  // -------------------------------------------------------------------
  Wire.begin();        // I2C
  Serial.begin(9600);  // SERIAL
  // INIT TMP101 - SET RESOLUTION TO 12 Bits
  Wire.beginTransmission(TMP101);
  Wire.write(0x01);    // Configuration Register
  Wire.write(0x60);    // R0 and R1 = 1
  Wire.endTransmission(); 

  UpdateDAC();

  dds.begin();
  dds.setFrequencyHz(0, FREQ);
  dds.selectFrequencyRegister(0);
  dds.enable();
}



void UpdateDAC() 
{
  unsigned long msb = (SetPointDAC & 0xFF00) >> 8 ;
  unsigned long lsb = SetPointDAC & 0xFF ;
  Wire.beginTransmission(DAC8571);
  // CONTROL BYTE
  // Write temporary register and load
  // DAC with data
  Wire.write(0x10);
  // MSB 
  Wire.write(msb);
  // LSB 
  Wire.write(lsb);
  Wire.endTransmission();
}

void UpdateHeatPower() 
{
  // VOLTAGE
  HeatPowerVolt = map(analogRead(HeatPowerPin),0,1023,0.0,19.9);
  HeatPower = HeatPowerVolt * HeatPowerVolt / 0.16666666666666  ;
}

void UpdateCurrentTemp() 
{
  Wire.beginTransmission(TMP101);
  Wire.write(0x00);
  Wire.endTransmission();
  Wire.requestFrom(TMP101,2);
  int temp_hi = Wire.read();         
  int temp_lo = Wire.read();        
  int temp = (( temp_hi << 8 ) | temp_lo ) >> 4 ;
  CurrentTemp = (CurrentTemp + temp * 0.0625) / 2.0 ;
}


void UpdateOLED() 
{
  display.clearDisplay();
  display.drawLine(0, 12, 128, 12, WHITE);
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0,0);
  display.println("**** STANDARDMOD ****");
  display.setTextSize(1);
  display.setCursor(0,17);
  display.print("CURRENT  : ");display.print(CurrentTemp,2);
  display.println(" C");
  display.drawCircle(99, 18, 1, WHITE);
  display.setCursor(0,29);
  display.print("SETPOINT : 75.00");
  display.println(" C");
  display.drawCircle(99, 29, 1, WHITE);
  // display.println(" V");
  display.setCursor(0,41);
  display.print("HEATING  : ");display.print(HeatPower,0);
  display.println(" mW ");
  display.setCursor(0,53);
  display.print("STATUS : ");
  if (abs(CurrentTemp-75.0) < 0.6) display.print("RELIABLE");
  else display.print("OUT OF SPEC");
  delay(100);
  digitalWrite(BEEPER, LOW);
  display.drawLine(0, 63, 128, 63, WHITE);
  display.display();
}


// ///////////////////////////////////////////////////////////// 


void loop() 
{
  UpdateCurrentTemp() ;
  UpdateHeatPower() ;
  UpdateOLED() ;
  Serial.println(CurrentTemp,3);
  delay(999) ;
}


// ///////////////////////////////////////////////////////////// 
// END OF FILE.
// ///////////////////////////////////////////////////////////// 

✈ Performance

✈ Credits • Note of Thanks

✈ Share your thoughts