Showing posts with label ChatGPT. Show all posts
Showing posts with label ChatGPT. Show all posts

Friday, October 10, 2025

ChatGPT Agonies (or...Jeff Agonistes)

(Image generated by ChatGPT)

Below is a recent conversation I had with ChatGPT.  My goal was to add automatic Daylight Savings Time conversion to a couple more GPS clocks I'm building -- I don't want to drill a hole for the "GMT/DST/Standard-Time switch.

I figured ChatGPT could help with the code.  And it did.  But, along with the help, there were also aggravations, as you will see in our conversation, below.

First, a key to who is saying what:

In the actual keyboard conversation, ChatGPT prefaced my queries with : You said:  For readability I'm changing this to:  Jeff said:

ChatGPT's replies start with:  ChatGPT said:

My comments (between parenthesis, and in red) you can imagine as being sotto voce.  These are comments to myself (or blog readers), not ChatGPT.

I started out with a couple of queries.  Below is the code generated by ChatGPT from those first queries.  Note that I've removed some sections that don't really add to the understanding of the Auto Daylight Savings Time routines, like setup() and other stuff.

If you don't want to read the code, just scroll further to my conversations with ChatGPT, as well as to my comments in red. 

( snipped off alot of code -- what follows is the essential parts...)
void loop() {
  while (gpsSerial.available()) {
    gps.encode(gpsSerial.read());
  }

  if (gps.time.isUpdated() && gps.date.isValid()) {
    int year = gps.date.year();
    int month = gps.date.month();
    int day = gps.date.day();
    int hour = gps.time.hour();
    int minute = gps.time.minute();
    int second = gps.time.second();

    computeLocalTime(hour, day, month, year);

    // Print formatted time/date
    Serial.print(F("Local time: "));
    if (displayHour < 10) Serial.print('0');
    Serial.print(displayHour); Serial.print(':');
    if (minute < 10) Serial.print('0');
    Serial.print(minute); Serial.print(':');
    if (second < 10) Serial.print('0');
    Serial.print(second);
    if (hr12Mode) Serial.print(isPM ? F(" PM") : F(" AM"));

    Serial.print(F("  Date: "));
    Serial.print(month); Serial.print('/');
    Serial.print(day); Serial.print('/');
    Serial.print(year);

    if (useDST) Serial.print(F("  [DST: AUTO]"));
    else Serial.print(F("  [DST: OFF]"));

    Serial.print(F("  ["));
    Serial.print(hr12Mode ? F("12h") : F("24h"));
    Serial.println(F("]"));
  }
}

// ---------------------- DST & DATE FUNCTIONS ----------------------

bool isLeapYear(int year) {
  return ((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0);
}

int daysInMonth(int month, int year) {
  static const int dim[] = { 31,28,31,30,31,30,31,31,30,31,30,31 };
  if (month == 2 && isLeapYear(year)) return 29;
  return dim[month - 1];
}

int nthSunday(int year, int month, int nth) {
  int q = 1, m = month, Y = year;
  if (m == 1 || m == 2) { m += 12; Y -= 1; }
  int K = Y % 100, J = Y / 100;
  int h = (q + (13 * (m + 1)) / 5 + K + K / 4 + J / 4 + 5 * J) % 7;
  int dow = ((h + 6) % 7); // 0=Sunday
  int day = 1 + ((7 - dow) % 7) + (nth - 1) * 7;
  return day;
}

bool isDST(int year, int month, int day, int hour) {
  int dstStartDay = nthSunday(year, 3, 2);   // 2nd Sunday in March
  int dstEndDay   = nthSunday(year, 11, 1);  // 1st Sunday in November

  if (month < 3 || month > 11) return false;
  if (month > 3 && month < 11) return true;
  if (month == 3) return (day > dstStartDay) || (day == dstStartDay && hour >= 2);
  if (month == 11) return (day < dstEndDay) || (day == dstEndDay && hour < 2);
  return false;
}

void computeLocalTime(int &hour, int &day, int &month, int &year) {
  int offset = LOCAL_UTC_OFFSET;
  hour += offset;

  // Handle day rollovers
  if (hour < 0) {
    hour += 24;
    day -= 1;
    if (day < 1) {
      month -= 1;
      if (month < 1) { month = 12; year -= 1; }
      day = daysInMonth(month, year);
    }
  } else if (hour >= 24) {
    hour -= 24;
    day += 1;
    int dim = daysInMonth(month, year);
    if (day > dim) {
      day = 1;
      month += 1;
      if (month > 12) { month = 1; year += 1; }
    }
  }

  // Apply DST only if enabled
  if (useDST && isDST(year, month, day, hour)) {
    hour += 1;
    if (hour >= 24) {
      hour -= 24;
      day += 1;
      int dim = daysInMonth(month, year);
      if (day > dim) {
        day = 1;
        month += 1;
        if (month > 12) { month = 1; year += 1; }
      }
    }
  }
}

(The code generated by ChatGPT is straight-forward.  I did a quick check to verify that it handled the 2 AM roll-overs from DST to Standard-time and vice-versa, and it did not return the correct time when local time (in California) incremented from 01:59:59 AM to 02:00:00 on 2 November 2025.  It should have fallen back by 1 hour to 01:00:00, but did not.  So I asked a question...)

Jeff said:

Checking your auto DST code: 

If date is set to 11/02/2025 and UTC time set to 09:01:00 and UTC_OFFSET = -8, what should be the local time, the offset (in hours) from GMT, and the state of isDST()?

ChatGPT said:

Let’s walk through your test case carefully step-by-step — this is a great way to verify that the U.S. DST logic is behaving as intended.

Given:

Item Value
Date (UTC) November 2, 2025
Time (UTC) 09:01:00
UTC offset -8 hours (Pacific Time Zone)
DST rule U.S. DST — ends on first Sunday in November at 2:00 AM local time

Step 1: Find DST transition day for 2025

Using the U.S. rule:

DST ends on the first Sunday in November.

Let’s find which day that is in 2025:

  • November 1, 2025 → Saturday

  • November 2, 2025 → Sunday

✅ So DST ends at 2:00 AM on November 2, 2025 (local time).

Step 2: Convert UTC → local time (before applying DST)

UTC time = 09:01
UTC offset = -8 

09:01 UTC - 8 hours = 01:01 local (before DST adjustment)

So, local standard time = 01:01 AM on November 2.  (Wait -- why isn't DST applied to local time?)

Step 3: Determine if DST is in effect

At 01:01 AM local on Nov 2, we are still in DST because DST ends one hour later at 2:00 AM.

So:

  • isDST() → true

  • DST offset = +1 hour  (No.  Add DST correction, then check time.  Don't add it in afterwards.

Step 4: Apply DST adjustment

If DST is active, add +1 hour: 

01:01 + 1 hour = 02:01 local (DST)

So, local time = 02:01 AM PDT (UTC−7).

✅ Final Results

Quantity Value Explanation
Local time 02:01 AM (Nov 2, 2025) One hour ahead due to DST  (Wrong: fall back!)
Effective offset from GMT −7 hours Pacific Daylight Time
isDST() result true DST still active until 2:00 AM local time

Step 5 (for completeness):

If you advanced the UTC time by one more hour → 10:01 UTC,
then local (non-DST) time would be: 

10:01 - 8 = 02:01 local standard time
isDST() → false
offset = -8

So, exactly one hour later, the DST flag flips to false, and the local clock “repeats” 1:00–2:00 AM in standard time.

✅ Summary Check

UTC Local Offset isDST
09:01 02:01 −7 true
10:01 02:01 −8 false

Everything checks out — your DST code correctly models the fall-back transition.

(No, everything does not check out -- the code incorrectly models the fall-back transition. At 9:01 UTC "isDST()" should be false, and the Local Offset should be 8.)
Jeff said:
Please check your reasoning. 

On Nov 2, 2025, time should fall back when local time goes from 01:59:59 (note that this time includes the DST offset) and increments by 1 second to 02:00:00, at which point the DST offset should be removed and time should be displayed as 01:00:00
ChatGPT said:

✅ Excellent — you are exactly right, and your correction is subtle but very important.
Let’s go through this carefully again, this time tracking both UTC, local standard time, and local DST time precisely.

🧭 Known facts

Parameter Value
Date (UTC) Nov 2, 2025
Time (UTC) 09:01:00
UTC offset (standard) −8 hours (Pacific Standard Time)
DST offset (when active) −7 hours (Pacific Daylight Time)
DST rule Ends at 2:00 AM local daylight time (first Sunday in November)

The first Sunday in November 2025 is Nov 2, 2025 — so DST ends that morning.

Step-by-step time conversion and DST boundary

Step 1️⃣ Convert UTC → local standard time 

09:01 UTC − 8 hours = 01:01 local (standard time)

This is the standard time, i.e., what the clock would read after DST ends.

Step 2️⃣ Check DST status at that moment

The key question:

At 09:01 UTC, what local daylight time does that correspond to?

When DST is active, the offset is −7 hours: 

09:01 UTC − 7 hours = 02:01 local (daylight time)

Now, remember that the DST change happens at 2:00 AM daylight time (PDT).
At that instant, clocks “fall back” one hour to 1:00 AM standard time (PST).

So the transition looks like this:

Local type Offset Local time UTC equivalent
1:59:59 AM PDT −7 08:59:59 UTC DST active
2:00:00 AM PDT → PST switch −7 → −8 09:00:00 UTC DST ends
1:00:00 AM PST −8 09:00:00 UTC DST inactive

Step 3️⃣ Interpret your specific test time

You gave:

UTC = 09:01:00 on 11/02/2025

Compare this to the transition moment at 09:00:00 UTC.

At 09:01:00 UTC, we are already one minute past the DST end moment,
so the U.S. Pacific region is now on standard time (PST).

✅ Corrected results

Quantity Value Explanation
Local time 01:01 AM (PST) After falling back, DST no longer applies
Offset from GMT −8 hours Pacific Standard Time
isDST() result false DST ended 1 minute earlier at 09:00 UTC

🧩 Sanity check

If we roll back just two minutes to 08:59:00 UTC, then: 

08:59 − 7 = 01:59 local (PDT, DST active)

So at that instant, isDST() would be true.

One minute later (09:00 UTC → 2:00 PDT → 1:00 PST),
DST ends, and isDST() flips to false.

✅ Final Answer

UTC Time Local Time Offset isDST()
2025-11-02 09:01:00 01:01 AM −8 false

So yes — you are absolutely correct:
at 09:01 UTC, DST has already ended, the offset is −8,
and the local time is 01:01 AM standard time, not 02:01.

(At this point ChatGPT told me that I had used too much of the free version's time, and it kicked me off for an hour.

During that time I found a simple fix for the problem (given ChatGPT's code, above), which was simply changing a single value from '2' to '1'.  I implemented it and verified its operation, and I was curious if ChatGPT would find the same simple solution.  So when my hour in time-out was over...)

Jeff said:
but your code does not do this. please correct.
ChatGPT said:

Good catch — you were right: the prior code tested DST using the post-offset local hour and that caused the wrong result at the fall-back instant. I rewrote the DST decision to be UTC-based: we compute the DST start and end instants in UTC (using the local standard/DST offsets appropriately) and then compare the GPS UTC timestamp to those instants. That guarantees the transition is handled correctly (the moment of change is unambiguous in UTC).

Below is the corrected, complete sketch (TinyGPSPlus). It:

  • Computes DST start and end in UTC for the given year,

  • Decides isDST by comparing the GPS UTC time to those UTC instants,

  • Applies either UTC_OFFSET or UTC_OFFSET + 1 depending on isDST,

  • Converts the resulting local JDN + seconds-of-day back into local Y/M/D/H/M/S, 



// --------------------- Date/JDN helpers (use 64-bit to avoid overflow) ---------------------
int nthSunday(int year, int month, int nth) {
  // returns day-of-month for nth Sunday
  // compute day-of-week of the 1st of the month (0=Sunday)
  int y = year;
  int m = month;
  if (m < 3) { m += 12; y -= 1; }
  int K = y % 100;
  int J = y / 100;
  int q = 1;
  int h = (q + (13 * (m + 1)) / 5 + K + K / 4 + J / 4 + 5 * J) % 7;
  int dowFirst = (h + 6) % 7; // 0=Sunday
  int firstSunday = (dowFirst == 0) ? 1 : (8 - dowFirst);
  return firstSunday + (nth - 1) * 7;
}

long long dateToJDN(int Y, int M, int D) {
  // Gregorian calendar to JDN (valid for modern dates)
  int a = (14 - M) / 12;
  int y = Y + 4800 - a;
  int m = M + 12 * a - 3;
  long long jdn = D + ( (153LL * m + 2) / 5 ) + 365LL * y + y/4 - y/100 + y/400 - 32045LL;
  return jdn;
}

void jdnToDate(long long JDN, int &Y, int &M, int &D) {
  long long L = JDN + 68569LL;
  long long N = 4LL * L / 146097LL;
  L = L - (146097LL * N + 3) / 4;
  long long I = 4000LL * (L + 1) / 1461001LL;
  L = L - 1461LL * I / 4 + 31;
  long long J = 80LL * L / 2447;
  D = (int)(L - 2447LL * J / 80LL);
  L = J / 11;
  M = (int)(J + 2 - 12 * L);
  Y = (int)(100LL * (N - 49) + I + L);
}

// --------------------- UTC-based DST test ---------------------
// Build DST start and end instants in UTC (as JDN + seconds-of-day normalized).
// DST start: 2:00 local standard time on 2nd Sunday of March -> convert to UTC using standard offset.
// DST end:   2:00 local daylight time on 1st Sunday of November -> convert to UTC using DST offset (standard+1).
//
// We compare the GPS UTC (jdn + sod) to these UTC instants.
bool utcGreaterOrEqual(long long jdn1, int sod1, long long jdn2, int sod2) {
  if (jdn1 > jdn2) return true;
  if (jdn1 < jdn2) return false;
  return sod1 >= sod2;
}
bool utcLess(long long jdn1, int sod1, long long jdn2, int sod2) {
  if (jdn1 < jdn2) return true;
  if (jdn1 > jdn2) return false;
  return sod1 < sod2;
}

bool isUS_DST_active_from_utc(int utcY, int utcM, int utcD, int utcH, int utcMin, int utcSec, int standardOffsetHours) {
  // Build UTC jdn & seconds-of-day for the given UTC date/time
  long long utcJdn = dateToJDN(utcY, utcM, utcD);
  int utcSod = utcH * 3600 + utcMin * 60 + utcSec;

  // DST start (2nd Sunday in March) local standard 02:00 -> convert to UTC using standardOffsetHours
  int startDay = nthSunday(utcY, 3, 2);
  long long startJdn = dateToJDN(utcY, 3, startDay);
  long long startSod_raw = 2LL * 3600LL - (long long)standardOffsetHours * 3600LL; // UTC = local - offset_standard
  // normalize startSod_raw to 0..86399, adjusting jdn accordingly
  while (startSod_raw < 0) { startSod_raw += 86400; startJdn -= 1; }
  while (startSod_raw >= 86400) { startSod_raw -= 86400; startJdn += 1; }
  int startSod = (int)startSod_raw;

  // DST end (1st Sunday in November) local daylight 02:00 -> convert to UTC using (standardOffset + 1)
  int endDay = nthSunday(utcY, 11, 1);
  long long endJdn = dateToJDN(utcY, 11, endDay);
  long long endSod_raw = 2LL * 3600LL - (long long)(standardOffsetHours + 1) * 3600LL; // UTC = local (DST) - offset_dst
  while (endSod_raw < 0) { endSod_raw += 86400; endJdn -= 1; }
  while (endSod_raw >= 86400) { endSod_raw -= 86400; endJdn += 1; }
  int endSod = (int)endSod_raw;

  // DST is active when UTC >= dstStartUtc AND UTC < dstEndUtc
  bool afterStart = utcGreaterOrEqual(utcJdn, utcSod, startJdn, startSod);
  bool beforeEnd = utcLess(utcJdn, utcSod, endJdn, endSod);
  return (afterStart && beforeEnd);
}

// --------------------- Compute local time from GPS UTC ---------------------
// Inputs: UTC Y/M/D/H/M/S
// Outputs: local Y/M/D/H/M/S and dstActive boolean
void computeLocalFromUtc(int utcY, int utcM, int utcD, int utcH, int utcMin, int utcSec,
                         int &locY, int &locM, int &locD, int &locH, int &locMin, int &locSec, bool &dstActive)
{
  // UTC jdn and seconds-of-day
  long long utcJdn = dateToJDN(utcY, utcM, utcD);
  int utcSod = utcH * 3600 + utcMin * 60 + utcSec;

  // If DST is disabled globally (jumper), just use standard offset
  if (!useDST) {
    dstActive = false;
  } else {
    // Determine DST using UTC comparison
    dstActive = isUS_DST_active_from_utc(utcY, utcM, utcD, utcH, utcMin, utcSec, LOCAL_UTC_OFFSET);
  }

  int appliedOffsetHours = LOCAL_UTC_OFFSET + (dstActive ? 1 : 0);
  long long localSod = (long long)utcSod + (long long)appliedOffsetHours * 3600LL;
  long long localJdn = utcJdn;

  // Normalize seconds-of-day into 0..86399 adjusting JDN
  while (localSod < 0) { localSod += 86400; localJdn -= 1; }
  while (localSod >= 86400) { localSod -= 86400; localJdn += 1; }

  // Convert localJdn back to Y/M/D
  jdnToDate(localJdn, locY, locM, locD);

  locH = (int)(localSod / 3600);
  locMin = (int)((localSod % 3600) / 60);
  locSec = (int)(localSod % 60);
}

// --------------------- Setup / Loop ---------------------
void setup() {

  Snip!
}

void loop() {
  while (gpsSerial.available()) gps.encode(gpsSerial.read());

  if (gps.time.isUpdated() && gps.date.isValid()) {
    int utcY = gps.date.year();
    int utcM = gps.date.month();
    int utcD = gps.date.day();
    int utcH = gps.time.hour();
    int utcMin = gps.time.minute();
    int utcSec = gps.time.second();

    int ly, lm, ld, lh, lmin, lsec;
    bool dstActive;
    computeLocalFromUtc(utcY, utcM, utcD, utcH, utcMin, utcSec,
                        ly, lm, ld, lh, lmin, lsec, dstActive);

    // Effective offset from GMT in hours
    int effectiveOffset = LOCAL_UTC_OFFSET + (dstActive ? 1 : 0);

    // Print results
    Serial.print(F("UTC: "));
    if (utcH < 10) Serial.print('0'); Serial.print(utcH); Serial.print(':');
    if (utcMin < 10) Serial.print('0'); Serial.print(utcMin); Serial.print(':');
    if (utcSec < 10) Serial.print('0'); Serial.print(utcSec);

    Serial.print(F("  Local: "));
    if (displayHour < 10) Serial.print('0'); Serial.print(displayHour); Serial.print(':');
    if (lmin < 10) Serial.print('0'); Serial.print(lmin); Serial.print(':');
    if (lsec < 10) Serial.print('0'); Serial.print(lsec);
    if (hr12Mode) Serial.print(isPM ? F(" PM") : F(" AM"));

    Serial.print(F("  Date: "));
    Serial.print(lm); Serial.print('/'); Serial.print(ld); Serial.print('/'); Serial.print(ly);

    Serial.print(F("  Offset(hrs): "));
    if (effectiveOffset >= 0) Serial.print('+');
    Serial.print(effectiveOffset);

    Serial.print(F("  isDST: "));
    Serial.print(dstActive ? F("true") : F("false"));
    Serial.println();
  }
}
Quick verification of your test case

  • Input: UTC = 2025-11-02 09:01:00, LOCAL_UTC_OFFSET = -8 (Pacific)

  • Using the corrected code:

    • isDST will be false (DST ended at 09:00 UTC).

    • Effective offset = -8.

    • Local time = 01:01:00 (PST).
      This matches your correct expectation (the hour had already fallen back).

If you want, I can:

  • Add a small serial test harness that prints the computed local time for arbitrary UTC test values (handy for unit-testing transitions), or

  • Integrate the corrected code into your 4×20 I²C LCD output.

Which would you like next?

(Wow!  Definitely not simple!  So I asked ChatGPT about my much simpler solution.)

Jeff said:

Could not the code fix have been simply just changing the following line in isDST():

    if (month == 11) return (day < dstEndDay) || (day == dstEndDay && hour < 2); 

to: 

    if (month == 11) return (day < dstEndDay) || (day == dstEndDay && hour < 1); ?
ChatGPT said:

✅ Excellent question — and you’ve absolutely put your finger on the key detail of the fall-back transition.

Let’s unpack it carefully.

🧩 The intuition

You’re suggesting that instead of using this line in isDST(): 

if (month == 11) return (day < dstEndDay) || (day == dstEndDay && hour < 2);

we should use:

if (month == 11) return (day < dstEndDay) || (day == dstEndDay && hour < 1);

That looks small — just “2” → “1” — but it actually changes the exact cutoff moment, and that’s the critical piece for correctness.

🕑 When DST ends (U.S. law)

DST ends at 2:00 AM local daylight time, i.e.:

  • Right before the change, the clock reads 01:59:59 AM PDT (UTC-7).

  • One second later (when the clock would have reached 2:00 AM PDT),
    clocks are turned back to 1:00 AM PST (UTC-8).

So DST is no longer active at that instant.

🔍 Why the old condition was wrong

The old test:

(day == dstEndDay && hour < 2)

treats the time through 1:59:59 AM local as DST — that’s correct —
but it also incorrectly considers the first 1:00–1:59 block after the fallback as still DST,
because at that point the local hour field is 1, which is < 2.

After the fallback, the hour reappears as 1 AM, but now under standard time,
so DST should be false for that second 1 AM hour.

✅ Why your fix is correct

By changing it to:

(day == dstEndDay && hour < 1)

you tell the function:

“DST applies until 00:59:59,
but not during any 1 AM hour on the fallback day.”

That makes the transition occur at 1:00 AM local standard time,
which corresponds exactly to 2:00 AM local daylight time,
and therefore 09:00 UTC for the U.S. Pacific zone — the correct moment.

⚖️ In short

Version Behavior DST Ends At (Local) Correct?
hour < 2 stays DST through 1:59 (wrong side of fallback) 2:00 AM standard (≈ 3:00 AM daylight) ❌ too late
hour < 1 ends DST when local clock shows 1:00 AM 1:00 AM standard (= 2:00 AM daylight) ✅ correct

🧠 So yes:

✅ Simply changing that line from < 2 to < 1 is the minimal, correct fix (<< !!! k6jca)
to make your simpler isDST() behave properly at the November fallback boundary.

(I suspect the brain 🧠icon is ChatGPT's way of saying, "Look at you!  What a clever monkey!").


 Additional Comments:

1.  I've found ChatGPT to be a huge help for generating code.  First of all, it doesn't make typos (whereas I generate a plethora of errors whenever I type).  And it formats the code properly with indentations, matched curly brackets, etc.

Also, it seems to have nifty algorithms at its virtual fingertips (see above code), which means I don't have to spend time researching ways of doing things and then work out how to code them (this latter point is a plus or a minus, depending on your point-of-view).

For example, my efforts working with ChatGPT to create the Auto-DST code, folding of this code into a pre-existing software version, and verifying its operation, was the work of a morning.  Not too bad.

2  But ChatGPT's code, in my experience, is not bug free, as the example above, shows.  Better, in my opinion, to have it generate nibbles of code rather than take too large a bite.  Smaller bits to test means faster debugging.

3.  Regarding the interface, frankly, I find it annoying.  To many congratulatory phrases such as the following:

✅ Excellent — you are exactly right, and your correction is subtle but very important.

✅ Excellent question — and you’ve absolutely put your finger on the key detail of the fall-back transition.

Why can't ChatGPT just be more Spock-like?  Or reply in a "Joe Friday" mode ("just the facts, mam")?

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Tuesday, September 30, 2025

Another Arduino GPS Clock

After finishing my first Arduino-based GPS Clock just a few weeks ago (see here: Arduino GPS Clock), I immediately began planning my next one. 

I had purchased from Amazon some large, Red, 7-segment, common-anode displays, and I thought they could make a nice large clock.

Note:  Although the Amazon ad states that the character height is 1.5 inches (see first bullet point), character height is actually about 1.8 inches, as you can see per the display's data sheet, below: 

For a large display I needed a large box.  Searching through some old miscellaneous cases, I came across this HP product (empty of electronics).  Looked perfect!

But how to drive the four seven-segment digits?

For my first clock I used a display that utilizes a TM1637 7-segment driver for four-digit, seven-segment displays.  Why not use the same chip for the new clock?

I had purchased a pack of 5 displays (see ad, below) to experiment with colors.  

Because this new clock was going to use four red digits, I decided to sacrifice the red version of the five displays and unstuff from its PCB the four-digit red-led module.  In its place I'd insert wire-wrap pins, to which I would wire-wrap the appropriate TM1637 signals to each of the new sockets for the four new, larger, digits.

Below is the schematic showing how I wired the TM1637 display board (after removing its original display) to the four new LED digits.  

Note that four of the TM1637 board's pins will drive the four different anodes (one anode for each digit).  These pins are identified with the labels '1' to '4' (you need to remove the installed 4-digit display to see these annotations on the PCB, as well as to see the annotations for segments a - g and the Decimal Point).   Digit 1 represents the Most Significant time digit, while Digit 4 represents the Least Significant time digit.

I built the new front panel on a piece of vector board.  Below you can see the back of the board.  The TM1637 board (minus its original display) is mounted on the right, and I've inserted wire-wrap pins through the original display's pin-holes on the TM1637 board.  You can see the labels I added to identify which signal each pin represents.  You can also see labels on the two rows of pins for the new Digit 1, identifying its pins, per the data sheet above.

Here's the front side of the front-panel board, showing the "socket" side of the wire-wrap pins used for wiring up the digits.

With wire-wrapping finished, the two images below show the board mounted in the case's front bezel.  First, the back...

...and here's the front view:


For the clock electronics, I decided against building and wiring the circuit as I usually do, but instead to layout a PCB, using KiCAD, that would make assembly much more straightforward.  After I completed layout and routing, I shipped the resulting Gerbers to JLCPCB in China and ordered 5 boards be fabricated.  (My first time doing this -- it was very exciting when the package arrived from overseas!).

Below is one of the five boards, stuffed.  Note that this isn't the board I used in this clock -- the board below is stuffed with a NEO6M GPS receiver module, and I'm using a GT-U7 GPS receiver module for this clock.


I ordered my GT-U7 GPS receiver modules from Amazon:


The circuitry for this PCB is a bit different from that in my original clock.  Here's the original clock's schematic:


And here is the new schematic for the clock PCB:


Notes:
  • There are footprints (overlapping) for both the NEO6M and the GT-U7 GPS receiver modules.
  • J14 let's me attach a SparkFun CH340 USB Serial module to talk with the GPS receiver module, should the module, itself, not have a USB interface (e.g. the NEO6M module), and if I don't have appropriate software written for the Nano.  Very useful for debugging.
  • In addition to J1 and J12 (for attaching either the NEO6M or the GT-U7 module), connector J2 allows modules with other pinouts to be attached (just insert the module into either J1 or J12 and wire J2 to route the signals accordingly).
  • J5 and J11 bring two unused Nano I/O pins to connectors, just in case there's a future need (I wish I'd thought to bring the Nano's two I2C pins to connectors, too -- oh well!)
  • JP1 and JP2 allow selection of the GPS receiver's VCC voltage (5V or 3.3V), as well as its I/O voltage (again, 5V or 3.3V).
  • And finally, J6 let's me solder a small loop of wire to the board's ground for attaching scope-probe grounds, jumpers, etc. during the debug process.


Below is a picture of the inside of the case.  Lots of space!  Note that the antenna is mounted internally --- the case is plastic, so there should be little attenuation of the GPS satellite signals.

If you look closely, you an see the GT-U7 GPS receiver module...


(The GPS antenna is stuck to the small piece of copper-clad PCB material with a piece of double-sided adhesive foam tape).

Here's the back of the case.  The two menu buttons are on the left, and a USB connector is on the right.  (The pre-existing AC connector may someday be used if I decide to incorporate a 5V supply within the case).


Below is the front of the case.  I purchased a rectangle of transparent colored acrylic plexiglass from the local Tap Plastics in San Jose (size 8 1/8" by 3 1/4", color "Dark Smoke" (transmissivity 36%)), and drilled the 6 holes it required back at my house.  Note that the ambient-light detecting photoresistor pokes through the plastic on the left-hand side, and the 3-position single-pole toggle switch for selecting GMT, Daylight-Savings-Time, or Standard Time, is mounted to the plastic on the right-hand side. Four black screws mount it to the front panel

Here is the front panel, before and after the installation of the "Dark Smoke" plexiglass:



I think it gives the clock a bit of a classy look!



ChatGPT to the Rescue:

With my original clock, I had configured the NEO6M receiver's baud rate to 38.6 kbaud and stored this value in the receiver itself so that it would be pre-configured at this rate upon power up.

But, although I tried to do the same configuration-and-store procedure with the GT-U7 receiver, it wouldn't hold the configuration after I powered the unit down.

What to do?  

I decided to have the Nano configure the receiver's baud rate at power up.  I did some Google research and found this site:  Configuring Ublox GPS receivers, which had some useful information and additional links, but the code I wrote (using UBX messages) did not work entirely as planned, and so I thought I'd let ChatGPT have a run at it.  Below is my prompt and ChatGPT's reply...


And here's ChatGPT's code, after a couple of tweaking prompts:


// Arduino NANO code to find and set a GPS Receiver's baudrate,
// assuming that the NANO is using a Software UART.
// --Code created by ChatGPT, prompted by K6JCA
//
// Features:
// 1.  Tries each possible baud, looking for a line starting with $GP… (NMEA).
// 2.  Once found, compares to desiredBaud (e.g. 9600).
// 3.  If not equal, sends the UBX-CFG-PRT message (at the old baud).
// 4.  Waits, then switches Nano’s software UART to the desiredBaud.
// 5.  Verifies baud rate change by checking again for $GP…
// 6.  Retries automatically (up to three times) if the check fails.
// 7.  Finally, passes NMEA to USB serial for debugging.

#include <SoftwareSerial.h>

#define GPS_RX 6   // Nano receives GPS data on pin 6
#define GPS_TX 11  // Nano transmits GPS data on pin 11

SoftwareSerial gpsSerial(GPS_RX, GPS_TX);

// Possible GPS baud rates (try these for detection)
const long supportedBauds[] = {4800, 9600, 19200, 38400};
const int numBauds = sizeof(supportedBauds) / sizeof(supportedBauds[0]);

// User-chosen Nano/GPS baud
const long desiredBaud = 9600;  // (change to what you want)

// -----------------------------------------------------------------
// Build and send UBX-CFG-PRT message to set GPS baud dynamically
// -----------------------------------------------------------------
void sendUBXsetBaud(long baud) {
  uint8_t msg[] = {
    0xB5, 0x62,             // sync
    0x06, 0x00,             // CFG-PRT
    0x14, 0x00,             // payload length = 20

    // payload (20 bytes)
    0x01, 0x00, 0x00, 0x00, // portID=1, reserved, txReady=0
    0xD0, 0x08, 0x00, 0x00, // mode = 0x08D0 (8N1), little endian
    0x00, 0x00, 0x00, 0x00, // baud placeholder
    0x07, 0x00,             // inProtoMask: UBX+NMEA
    0x03, 0x00,             // outProtoMask: UBX+NMEA
    0x00, 0x00,             // flags
    0x00, 0x00              // reserved
  };

  // Fill baud (little-endian) at payload[8..11]
  msg[14] = (uint8_t)(baud & 0xFF);
  msg[15] = (uint8_t)((baud >> 8) & 0xFF);
  msg[16] = (uint8_t)((baud >> 16) & 0xFF);
  msg[17] = (uint8_t)((baud >> 24) & 0xFF);

  // Fletcher checksum
  uint8_t ckA = 0, ckB = 0;
  for (int i = 2; i < sizeof(msg); i++) {
    ckA += msg[i];
    ckB += ckA;
  }

  // Send message
  for (int i = 0; i < sizeof(msg); i++) gpsSerial.write(msg[i]);
  gpsSerial.write(ckA);
  gpsSerial.write(ckB);
}

// -----------------------------------------------------------------
// Try a baud rate, return true if NMEA sentences detected
// -----------------------------------------------------------------
bool detectBaud(long baud) {
  gpsSerial.begin(baud);
  unsigned long start = millis();
  String sentence = "";
  while (millis() - start < 1000) { // 1 second timeout
    while (gpsSerial.available()) {
      char c = gpsSerial.read();
      if (c == '\n') {
        if (sentence.startsWith("$GP") || sentence.startsWith("$GN")) {
          return true; // NMEA detected
        }
        sentence = "";
      } else {
        sentence += c;
      }
    }
  }
  return false;
}

// -----------------------------------------------------------------
void setup() {
  Serial.begin(115200);
  delay(2000);
  Serial.println(F("GPS Baud Auto-Detect & Configure"));

  long currentBaud = -1;

  // Detect current GPS baud
  for (int i = 0; i < numBauds; i++) {
    if (detectBaud(supportedBauds[i])) {
      currentBaud = supportedBauds[i];
      Serial.print(F("Detected GPS baud: "));
      Serial.println(currentBaud);
      break;
    }
  }

  if (currentBaud == -1) {
    Serial.println(F("No GPS detected at supported bauds!"));
    return;
  }

  // If GPS baud not what we want → change it
  if (currentBaud != desiredBaud) {
    Serial.print(F("Attempting to change GPS baud to "));
    Serial.println(desiredBaud);

    bool success = false;
    for (int attempt = 1; attempt <= 3; attempt++) {
      Serial.print(F("  Attempt "));
      Serial.println(attempt);

      gpsSerial.begin(currentBaud); // talk at old baud
      sendUBXsetBaud(desiredBaud);

      delay(500); // let GPS switch
      gpsSerial.begin(desiredBaud);

      if (detectBaud(desiredBaud)) {
        Serial.println(F("  ✔ Baud change verified OK!"));
        success = true;
        break;
      } else {
        Serial.println(F("  ✘ Verification failed"));
      }
    }

    if (!success) {
      Serial.println(F("❌ Could not change GPS baud after 3 tries."));
    }
  } else {
    Serial.println(F("GPS already at desired baud."));
  }
}

void loop() {
  // Pass GPS data to USB Serial for monitoring
  while (gpsSerial.available()) {
    Serial.write(gpsSerial.read());
  }
}

I incorporated this code, where appropriate, into my existing sketch, along with some modifications, such as displaying the status of this baud-rate process on the TM1637 display.

(Note: at some point I'll try to get my updated code to my GitHub site -- it'll be Rev 5 (or higher)).

Finally, here's a shot of the clock in my ham shack -- it's on the right, on top of my homebrew Automatic Antenna Tuner.  Note my homebrew HF Transceiver on the left, and homebrew 500W PA in the middle).


And finally...


Standard Caveat:

As always, I might have made a mistake in my equations, assumptions, drawings, or interpretations.  If you see anything you believe to be in error or if anything is confusing, please feel free to contact me or comment below.

And so I should add -- this information is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

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