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If you need a stable time base for something such as a clock project have a look at this DIY 1Hz Time Base project from The Hackers Bench. I see that the board that was used is one from our friends at Gadget Gangster. “In principal this circuit is extreemly simple. You build a crystal oscillator, and then you divide it’s output down to 1Hz. The crystal we’re going to use here run at 32.768 KHz ( 32768 Hz ). These are commonly called clock, or watch crystals. The significance of the value is that you can successively divide 32768 by 2 and eventually you will get to 1. There are other values that will do this (all multiples of 32768), but this value is very common. That means the crystal is cheap and easy to find.” |
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May 14th, 2011
Nifty. It’d also be awesome if the 4027 pins were brought out on a header; then you’d have a 1Hz-32KHz time base, selecting the clock speed you want by which pin on the header you use.
May 14th, 2011
I don’t mean to poo poo the work here but this is probably not a time base you would want to use for a clock with any “real” accuracy. I notice on the website there is no mention of performance i.e. deviation from “real” time. I have found through research and experimentation using crystals is not that easy to achieve out of the box accuracy and as such the need to calibrate is paramount. A typical 32.768kHz “watch” crystal will have a frequency tolerance of +/- 20ppm which would be +/-1.7 S/day. That is assuming the crystal load capacitance is correct and not pulling the frequency. Stray capacitance, cap ESR, even rosin left by soldering can add to the error; and of course temperature. I would be interested to see some performance numbers out of this timebase.
May 19th, 2011
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