25th August 2008 12:17 PM
Coop Build Coordinator
Thanks mike. I was not actualy building this clock But it looked like a good context for asking the question.
9th September 2008 04:40 AM
This one is software adjustable in case it runs slightly fast or slow.
9th September 2008 02:41 PM
What a horrible piece of code and it uses Timer0. If you do a search Mike (the OP) posted a very good method to adjust for crystal inaccuracies in software.
Originally Posted by Space Varmint
9th September 2008 02:49 PM
Personally I'm one of those types who tries to match the crystal frequency to the task at hand. Using the generic 4MHz or multiples thereof for everything always baffled me, after all crystals are about the same price and there are many common frequencies available. 19.6608MHz is a handy for both RTC & UART stuff.
10th September 2008 01:37 AM
Just use current limiting resistors on the segment lines and connect the transistor collectors to 12 volts and you can have whatever brightness you want.
If you want to keep it a one power supply project, use 12 volts as the power supply and generate the 5v with a voltage regulator (7805).
10th September 2008 07:07 AM
Hi Mike, WY6K,
Originally Posted by wy6k
Keeping in mind the 5v PIC pins, an NPN/PNP pair or N-FET/P-FET pair for the high side drivers does indeed work well with traditional multiplexed displays but it's a bit problematic for Charlieplexed displays.
Regards, Mike, K8LH
10th September 2008 07:18 AM
Unfortunately, that's about all that crystal frequency is good for (grin).
Originally Posted by blueroomelectronics
Using wierd crystal frequencies always baffled me but if you can show me how to accomplish any operation in exact 1 usec increments using one of those crystal frequencies then you'll have a convert (grin)...
10th September 2008 07:58 AM
I can see how a 19.6608MHz crystal is good for serial communications but how is it any better for a real time clock?
Last edited by Pommie; 10th September 2008 at 07:58 AM.
10th September 2008 08:30 AM
I can't see how it's any better for serial either, it works 100% perfectly with a 20MHz or 4MHz crystal - so how does getting an exact frequency match give any improvement?.
Originally Posted by Pommie
11th September 2008 12:26 AM
Ahhh. I see that now. In that case, you need another set of column transistors and invert the logic on the n-1 line? (I'm not really familiar with Charlieplexing, but I think I get it). MPU output drives base of NPN which pulls down the base of the PNP with it's emitter connected to 12 volts. Right?
Originally Posted by Mike, K8LH
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