On Dec 31, 2008, at 4:57 PM, Forrest Christian wrote:
>

> You might want to pick up an EasyPIC5 board from mikro-e, or their us
> distributor circuit-ed.   Plus, start with the free Mikro-Basic or
> Mikro-C compiler, both can be upgraded to the full version if needed
> later.  I might be inclined to point you toward BASIC, although if you
> can get your head around C, that would work as well or better.

I have been looking at Mikroelektronika's products for some time.  I  
have their free C compiler, and have wondered about the development  
boards.  (Interestingly, you can order the EasyPic5 directly from the  
Mikroe website for about $20 cheaper than from Circuit-Ed.)  The  
EasyPic5 looks like a good value.  However, since I have a pretty  
extensive junkbox, I wonder if a product like this would enhance my  
learning.  I already have the majority of any needed components that I  
can assemble on a solderless breadboard for experimenting and  
learning.  I'll admit to liking 'toys' though, and having everything  
on one board might be convenient.   Of course, like everyone else, I'm  
a bit more conservative in spending money nowadays.
>
> Most "line powered" clocks are actually timed from the 60 hz line.

I've always liked this option.  I have found line-based clocks to be  
as accurate if not more so than most crystal controlled clocks.  My  
understanding is the 60Hz line in the US / Canada is spot on, and I  
imagine the 50Hz throughout Europe is likely just as stable.  Some  
other countries, however, apparently do not have as reliable a power  
source, and xtal control is a better option.

>  If I was implementing a clock, I would take a ~6VAC transformer,  
> run the
> unfiltered AC through a resistor, and then a couple of clamp diodes  
> (aka
> reverse biased diode to VCC and to GND), and then into the T1CKI pin.
> In this way, each cycle of the AC line can increment the 16 bit  
> timer 2,
> and then it keeps track of how many 60hz "ticks" (might be 120Hz
> depending on how you wire it up) since the timer was reset.   It looks
> like the t1cki pin is schmitt triggered on the 'f887 datasheet I'm
> looking at, so this should be safe to do.   Once you have a counter
> counting cycles, then you can go from there.   Timer 1 may also be
> interesting.  I'd look strongly at the Microchip Clock app note  
> someone
> else mentioned.

I did not know how to do this previously!  I've always seen external  
xtal control.  I never thought that the line frequency itself might be  
buffered and used as an external oscillator.

>  Mikro-E actually has an addon board which has a
> Philips PCF8583, which is ready to go..   Other RTC chips might be
> better suited to your app, but this would get you going.
>

You are certainly a good spokesman for Mikro!   :-)

I'l give some serious thought to purchasing the EasyPic5 board.

Thanks!

Joe

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