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Making a watch using a PIC Answered

I want to make a wristwatch using a PIC to control the watch. How would I keep the time using it? Would I need a crystal and if so, how would I interface it with the PIC (how would it communicate with the PIC)?



If you are trying to use a PIC to drive the LCD of a watch that you have, it will be more difficult than it is worth. You will need to find documentation on the LCD to interface to it properly, and if that is not available you will have to determine it yourself by reverse engineering.

If this is jus a project for fun or for a class, you may want to consider making a clock instead. Your processor will need to do the work or counting and managing the rollover of hours and minutes properly. Some PICs may have internal real time clock functionality that could take care of some of that. Many PICs have internal oscillators that could eliminate the need for any external crystal or oscillator, but these are less accurate (only about 1% accurate). But, if this is just to demonstate for a class or to learn for your own benefit, it may not matter to you if it drifts over time.

Definitely visit the microchip web site to review their processors and download free applicatin notes and datasheets.

The rest of the effort would be updating a display of some sort. LCDs with parallel or serial interface are common and there are many articles on this site and elsewhere on how to interface them to a microcontroller.

With the internal oscillator, how much would it drift over, say, a month? And how would I program the PIC to take the time from the internal oscillator or would I just tell it to wait and it would be a second (if you see what I mean)?

If I recall, the tolerance on the internal oscillator is 1% according to the datasheet. So, it could drift as much as 36 seconds per hour. Over a month it could then drift 7.2 hours. Thats pretty bad for any clock, but it all depends on your accurace needs. Using an external oscillator or crystal circuit with a PIC is easy, and they have good app notes on it.

If you don't have real time clock (RTC) hardware in the micro or an external RTC chip, then you will need to set up timing loops or interrupts in the software. For example you may set up a loop to do nothing for some small time increment like 1 second , and every time this loop completes the counts for seconds, hours, and minutes will have to be updated and managed as necessary and whatever display you use will have to be updated.

OMG I do better looking at the sky.
Scanning the manual, there was mention of soft adjustment.


Yeah, I think everyone would do better looking at the sky if it's 7 hours out :)
Soft adjustment? Would that allow me to use it accurately for a month or so and then just reset it?

Go to page 10 of the user manual that tells you about adjusting the clock speed.
Also ibles Best Answer look up you need
Apparently the clock can be adjusted well enough for timing of several monthly
moon cycles.

Secret advice about clock adjustment:
Wrist watches depend on stable temperature ( Of Your Body ) your wrist to make
any watch run more accurately. Ergo, you must wear the LCD thingy while you
are adjusting the clock timing.
Other wise it will probably change once you put it on.


Cool site, now jamie c53 can go LCD already programmed.

I bet you could make a really nice job with a mobile phone display now.

That was always such sci-fi - and now its nothing like as advanced as we can now manage.

Right.... Dick Tracy was a newspaper comics detective
famous for his wrist radio when I was a boy.

The PIC can be driven with a crystal, for its own clock source.

+1 Steve.
Now, jamie c53 pick a Pic to use and ask a question
about how to program an interrupt clock routine :-D
A 7segment LED digit is easiest to run for a numeric output
so pick the Pic carefully avoid OTP types.
Don't use the Microchip site ( for info only ! ).
Do use Digi-Key or Newark because their stock you can acquire.