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 A few questions
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By: Anonymous: Brent () on Friday, January 27 2012 @ 11:49 AM PST (Read 1390 times)  
Anonymous: Brent

I just received my kit and optional Chronodot and haven't put it together yet, but I've been reading through the assembly instructions, and a few questions have popped into my head.

Even though I can't imagine why it would matter electrically, why is R11 an 1/8 watt resistor when all the others are 1/4 watt? Is it to avoid confusion with other resistors by making it a different size for the benefit of those unfamiliar with the color codes?

In a couple of closeup pictures on your website, I noticed that the AVR installed on the board was actually an ATmega328P Cool, not the ATmega168 supplied with the kit. After successfully building and testing my kit, my intent is to remove the '168 from the board (I'll be installing a socket during assembly Wink) and put in a '328P (properly programmed with the Arduino bootloader) in order to develop some custom firmware. Do you foresee any problems with using a '328P in place of the '168?

Can you please give me an overview of how the firmware makes use of the Chronodot. I don't see any connection from the 32 KHz or square-wave outputs of the Chronodot to the AVR, so I assume everything is being done over I2C. So is the Chronodot being continuously polled waiting for the next second to occur, or is it periodically polled to resynchronize the "standard" timekeeping code that exists in the firmware?

Thanks in advance,
Brent





       
   
By: Windell (offline) on Friday, January 27 2012 @ 12:41 PM PST  
Windell

why is R11 an 1/8 watt resistor when all the others are 1/4 watt? Is it to avoid confusion with other resistors by making it a different size for the benefit of those unfamiliar with the color codes?

Yes, that's it exactly.

Do you foresee any problems with using a '328P in place of the '168?

No, it can be used as a direct substitute.

So is the Chronodot being continuously polled waiting for the next second to occur, or is it periodically polled to resynchronize the "standard" timekeeping code that exists in the firmware?

The bulbdial comes with a very good 20 ppm crystal oscillator-- much nicer than the 50 ppm types normally found on "Arduino class" hardware. This manages almost all the timekeeping. The Chronodot is polled once per minute over I2C, and a correction is issued only when the time is off by more than two seconds-- something that will happen no more than a few dozen of times per month, in typical use.


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By: Anonymous: Brent () on Friday, January 27 2012 @ 01:05 PM PST  
Anonymous: Brent

Thank you for all that good info, and so quickly at that. I can already envision a plug-in Chronodot emulator board sporting a GPS receiver to take it to the next level Wink.

I forgot to mention previously what a nice kit I think this is. It's fun to look at, even unassembled Big Grin.

Best regards,
Brent





       
   



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