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blanham wrote:I'm trying to build an atomic clock using a CMAX CMMR-6 module from digikey and an arduino. This module outputs the raw WWVB data. Does anyone have experience decoding this data with Arduino?Yes. I have a sketch which listens to WWVB and decodes it, then uses the Arduino internal clock to synthesize its own time code which is then put onto one of the digital out pins. The internal clock keeps on running even when WWVB is not received. I use this exact receiver, in fact.
/**********************************************************************
* Clock WWVB Data Decode Frame Reject by capt.tagon
*
* WWVB receiver input on digital pin 2
**********************************************************************/
#define wwvbIn 2 // WWVB receiver data input digital pin
#define ledRxPin 4 // WWVB receiver state indicator pin
#define ledFramePin 6 // Data received frame indicator pin
#define ledBitPin 5 // LED data decoded indicator pin
#define ledMarkPin 7 // Data received mark inicator pin
// variable changed by interrupt service routine - volatile
volatile byte wwvbInState; // store receiver signal level
byte prevWwvbInState; // store previous signal level
unsigned int prevEdgeMillis; // store time signal was read
byte bitVal; // bit decoded 0, 1, Mark or Frame
boolean badBit = 0; // bad bit, noise detected
byte markCount = 0; // mark count, 6 pulses per minute
boolean prevMark = 0; // store previous mark
byte bitCount = 0; // bits, 60 pulses per minute
boolean frameError = 0; // set for frame reject
unsigned int errorCount = 0; // keep count of frame errors
void setup() {
pinMode(wwvbIn, INPUT);
pinMode(ledRxPin, OUTPUT);
pinMode(ledFramePin, OUTPUT);
pinMode(ledBitPin, OUTPUT);
pinMode(ledMarkPin, OUTPUT);
attachInterrupt(0, readLevel, CHANGE); // fire interrupt on edge detected
Serial.begin(9600);
lcdInit();
}
void loop() {
if (wwvbInState != prevWwvbInState) {
pulseValue();
prevWwvbInState = wwvbInState;
}
}
/******************************************************************
* pulseValue()
*
* determine pulse width 200ms = 0, 500ms = 1, 800ms = mark
******************************************************************/
void pulseValue() {
unsigned int edgeMillis = millis(); // save current time
if (wwvbInState == 1) { // rising edge
prevEdgeMillis = edgeMillis; // set previous time to current
}
else { // falling edge
int pulseLength = edgeMillis - prevEdgeMillis; // calculate pulse length millis
badBit = 0; // clear bad bit detected
digitalWrite(ledMarkPin, LOW);
digitalWrite(ledFramePin, LOW);
if (pulseLength < 100) { // less than 100ms, noise pulses
badBit = 1; // bad bit, signal pulse noise
}
else if (pulseLength < 350) { // 800ms carrier drop mark
// two sequential marks -> start of frame. If we read 6 marks and 60 bits
// (0-59), we should have received a valid frame
if ((prevMark == 1) && (markCount == 6) && (bitCount == 59)) {
bitVal = 3;
frameAccept(); // data decoded, accept frame
digitalWrite(ledFramePin, HIGH); // frame received, ready for new frame
markCount = 0; // start counting marks, 6 per minute
prevMark = 0; // set bit counter to one
bitCount = 0; // should be a valid frame
frameError = 0; // set frame error indicator to zero
errorCount = 0; // set frame error count to zero
}
else if ((prevMark == 1) && ((markCount != 6) || (bitCount != 59))) {
errorCount ++; // increment frame error count
frameReject(); // bad decode, reject frame data
digitalWrite(ledFramePin, HIGH); // apparent frame, wrong mark and bit count
markCount = 0; // bad start of frame set mark count to zero
prevMark = 0; // clear previous to restart frame
bitCount = 0; // set bit count to one
frameError = 1; // and indicate frame error
}
else { // 10 second marker
bitVal = 2;
markCount ++; // increment mark counter, 6 per minute
digitalWrite(ledMarkPin, HIGH); // mark received
prevMark = 1; // set mark state to one, following mark indicates frame
bitCount ++; // increment bit counter
}
}
else if (pulseLength < 650) { // 500ms carrier drop one
bitVal = 1;
digitalWrite(ledBitPin, HIGH); // bit indicator LED on, one received
prevMark = 0; // set mark counter to zero
bitCount ++; // increment bit counter
}
else { // 200ms carrier drop zero
bitVal = 0;
digitalWrite(ledBitPin, LOW); // bit indicator LED off, zero received
prevMark = 0; // set mark counter to zero
bitCount ++; // increment bit counter
}
if (badBit == 0) { // reject noise
timeDateDecode();
}
}
}
/******************************************************************************
* readLevel() {
*
* Pin 2 INT0 Interrupt Handler Reads pin state - flashes signal indicator LED
******************************************************************************/
void readLevel() {
wwvbInState = digitalRead(wwvbIn); // read signal level
digitalWrite(ledRxPin, wwvbInState); // flash WWVB receiver indicator pin
}
/******************************************************************************
* timeDateDecode()
*
* Decode function to extract BCD from data stream
******************************************************************************/
void timeDateDecode() {
// Display bit values to terminal screen, output delimited data stream with
// colons at mark and new line at frame start. DEBUG ROUTINES
if (bitVal == 3) {
Serial.print("<- Frame Decode\n : ");
}
else if (bitVal == 2) {
Serial.print(" : ");
}
else {
Serial.print(bitVal, DEC);
}
}
/******************************************************************************
* frameAccept()
*
* Accept function for completed frame decode
******************************************************************************/
void frameAccept() {
// future BCD decode here
}
/******************************************************************************
* frameReject()
*
* Reject function for bad frame decode
******************************************************************************/
void frameReject() {
// Display Frame Reject message, mark count bit count and sequential number
// of frame errors. DEBUG ROUTINES
Serial.print("\n ->Scratch<- Bad Data - Marks: ");
Serial.print(markCount, DEC);
Serial.print(" Bits: ");
if (bitCount < 10) {
Serial.print("0");
}
Serial.print(bitCount, DEC);
Serial.print(" Frame Errors: ");
if (errorCount < 10) {
Serial.print("0");
}
Serial.println(errorCount, DEC);
}
/*****************************************************************************
* Time display functions
*****************************************************************************/
// LCD routines to initialize LCD and clear screen
void lcdInit() { // using P H Anderson Serial LCD driver board
Serial.print("?G216"); // configure driver for 2 x 16 LCD
delay(300);
Serial.print("?BDD"); // set backlight brightness
delay(300);
Serial.print("?f"); // clear screen
Serial.print("?c0"); // set cursor off
}
epedersen wrote:Do you have the schematic of your project, I am trying to get one of the c-max devices working with your code and I am having troubles.Here's a schematic for the interface between the CMax CMMR-6P-60 board and the Arduino that I'm currently using.
Any assistance would be appreciated.
Thanks.
jesrandall wrote:I have in fact worked with this exact module. Signal sensitivity is good, however, you will have to add additional components to the digikey module. Several capacitors and an inductor are lacking in the completed version. This allows the user to fine tune the device since capacitor tolerances are often low and can be costly depending on how sensitive you need it to be.Please provide a schematic... Is this for filtering and smoothing the power?
jesrandall wrote:Now, since you are building a clock. Here's something to look out for. When I first designed it I used a multiplexing display to keep prices low. But, the multiplexing frequency SEVERELY interfered with the atomic radio reception. I then proceeded to the next logical step, spread spectrum clocking. This WILL dramatically improve reception, but you still must use all possible precautions to keep noise down. Mount the entire module and ferrite antenna away from the multiplexing display. I was building a large size clock with 7 watt power so the noise was very prominent. Spread spectrum, in theory (mathematically) can reduce effective power transmission on a given frequency to ZERO, but in practical terms this cannot be achieved.Multiplexed LED displays... I remember using an old TI-30/33/55 (not sure on model no?) calculator as a receiver live check. If you didn't hear the buzz... Any websites to educate myself on spread spectrum clocking/multiplexed displays?
epedersen wrote:Do you have the schematic of your project, I am trying to get one of the c-max devices working with your code and I am having troubles.Indicator LEDs
Any assistance would be appreciated.
Thanks.