Locate and syncronize timestamp

I have a raspberry without a real time clock which is creating minutelly files. To calculate the estimated time i have as indication the time that i pluged it off. I created a script like this:

    
    last_record='08_05_10_57';           % Correct time and date
    last_record_raspberry='13_03_14_33'; % Not correct time and date
    
    tmp_last_record = str2double(split(last_record(1:length(last_record)),'_'));
    tmp_last_record_raspberry = str2double(split(last_record_raspberry(1:length(last_record_raspberry)),'_'));
      

    month = tmp_last_record_raspberry(2)-tmp_last_record(2);
    day = tmp_last_record_raspberry(1)-tmp_last_record(1);
    hour  = tmp_last_record_raspberry(3)-tmp_last_record(3);
    minutes  = tmp_last_record_raspberry(4)-tmp_last_record(4);
       
    
    earthquake_record='07_05_19_45';     %I want to fix/locate this time with the corresponding file
    earthquake_record= str2double(split(earthquake_record(1:length(earthquake_record)),'_'));
        
        earthquake_record_raspberry=earthquake_record;
    earthquake_record_raspberry_day=earthquake_record_raspberry(1)+day;
    earthquake_record_raspberry_month=earthquake_record_raspberry(2)+month;
    earthquake_record_raspberry_hour=earthquake_record_raspberry(1)+hour;
    earthquake_record_raspberry_minutes=earthquake_record_raspberry(2)+minutes;
    earthquake_record_raspberry=[earthquake_record_raspberry_day;earthquake_record_raspberry_month;earthquake_record_raspberry_hour;earthquake_record_raspberry_minutes]

which corrects/locates the day and month of the raspberry with the real, but for minutes and seconds i have some problems e.g. 11:-19 instead of 10:41..

Can anyone help me?

Answer 1

[Steven Lord]

Rather than splitting the strings representing dates and times into vectors of numbers and trying to perform date and time arithmetic yourself, convert them into datetime arrays and let MATLAB do the arithmetic.

last_record='08_05_10_57';           % Correct time and date
last_record_raspberry='13_03_14_33'; % Not correct time and date

Based on your code this is arranged as day_month_hour_minute.

dt1 = datetime(last_record, 'InputFormat', 'dd_MM_HH_mm')

dt1 = datetime
   08-May-2024 10:57:00

dt2 = datetime(last_record_raspberry, 'InputFormat', 'dd_MM_HH_mm')

dt2 = datetime
   13-Mar-2024 14:33:00

What's the difference between the two dates?

difference = dt1-dt2

difference = duration
   1340:24:00

Let's change that format to days, hours, minutes, seconds.

difference.Format = 'dd:hh:mm:ss'

difference = duration
   55:20:24:00

Or to take into account leap year, etc. take the calendar difference.

difference2 = caldiff([dt2, dt1])

difference2 = calendarDuration
   1mo 24d 20h 24m 0s

If you have tabular data, you could use the datetime array as the RowTimes of a timetable array and use retime or synchronize on it.

[Ancalagon8]

This part did the job, so difference2 indicates the "error" of the last file.

dt1 = datetime(last_record, 'InputFormat', 'dd_MM_HH_mm')
dt1 = 08-May-2024 10:57:00

dt2 = datetime(last_record_raspberry, 'InputFormat', 'dd_MM_HH_mm')
dt2 = 13-Mar-2024 14:33:00

difference = dt1-dt2
difference2 = caldiff([dt2, dt1])
difference2 = 1mo 24d 20h 24m 0s

Assuming I want to detect a specific file e.g. at 07/05 19:40:

earthquake_record='07_05_19_45';
dt3 = datetime(earthquake_record, 'InputFormat', 'dd_MM_HH_mm')
dt3 = 07-May-2024 19:45:00

how to correct dt3 with difference2?

[Steven Lord]

I'm not 100% certain I understand what you're asking, but if you're asking how you can determine whether dt1 or dt2 was closer to dt3:

last_record='08_05_10_57';           % Correct time and date
last_record_raspberry='13_03_14_33'; % Not correct time and date
dt1 = datetime(last_record, 'InputFormat', 'dd_MM_HH_mm')

dt1 = datetime
   08-May-2024 10:57:00

dt2 = datetime(last_record_raspberry, 'InputFormat', 'dd_MM_HH_mm')

dt2 = datetime
   13-Mar-2024 14:33:00

earthquake_record='07_05_19_45';
dt3 = datetime(earthquake_record, 'InputFormat', 'dd_MM_HH_mm')

dt3 = datetime
   07-May-2024 19:45:00

abs(dt3-dt1) < abs(dt3-dt2)

ans = logical
   1

or

[~, location] = min(abs([dt1, dt2]-dt3))

location = 1

[Ancalagon8]

No, please let me make it more clear:

With difference2 I can calculate the error between dt1 (real time) and dt2 (wrong time from rasberry).

Now when I have another date and time (dt3-real time) and knowing difference2, I need to calcuiate the corresponding time (dt4 - wrong time from rasberry). Maybe something like

dt4 = dt3- differnce2

will do the work?

[Steven Lord]

The difference between two datetime arrays is a duration or a calendarDuration. You can add either of those to a datetime or subtract them from a datetime to get another datetime.

dt = datetime('now')

dt = datetime
   09-May-2024 16:43:40

du = days(1)

du = duration
   1 day

cdu = caldays(1)

cdu = calendarDuration
   1d

tomorrow1 = dt + du % datetime + duration = datetime

tomorrow1 = datetime
   10-May-2024 16:43:40

tomorrow2 = dt + cdu % datetime + calendarDuration = datetime

tomorrow2 = datetime
   10-May-2024 16:43:40

yesterday1 = dt - du % ditto for subtraction

yesterday1 = datetime
   08-May-2024 16:43:40

yesterday2 = dt - cdu

yesterday2 = datetime
   08-May-2024 16:43:40