STOPWATCH: PIC16F877A Questions

[helloiamkat]

Hi. I am planning to create a stopwatch using switches (to signal the start and end of the watch) and PIC16F877A. I plan to use C++ for my programming.

I have a question though, how fo I choose the oscillator? I mean, should I consider this since I want the timer to be like real time??

Also, what other factors should I consider?

I have been doing some reading and I figured I need to use Timer1 for my project.

Thanks! Will be waiting for your replies.

 

[amraldo]

C will be more suitable.
For real time, it is better to use an external RTC chip with the PIC or use a PIC with internal RTC.
The oscillator can be internal or external, I guess no problem with taht.
--
Amr

 

[helloiamkat]

With RTC do you mean DS1307 or DS1302? A friend suggested I should look into those.

 

[amraldo]

These are good options.
--
Amr

 

[betwixt]

A DS1302/1307 will be of no use if the timing accuracy has to be very accurate. Their counting intervals are too long.

I would suggest using timer interrupts to generate 10mS intervals then counting them in software. It would be more accurate than an external timer IC and uses less (none!) extra components.

Brian.

 

[amraldo]

Can it count 10 ms precisely?
--
Amr

 

[betwixt]

At 20MHz clock speed, the '877A timer can count internal clock cycles at 5MHz (= 200nS). Counting as slow as 10mS is VERY easy!

The DS130x ICs can only count in increments of one second, that's 100 times less precise.

Brian.

 

[amraldo]

My question is it wont be precise 10 ms.
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Amr