[sdiy] Timing : How close is close enough?

[Matthew Smith]

Quoth Tom Arnold at 2009-02-04 09:45...
...
> I know this could devolve into a religious debate, but I'm curious what
> people really think *is* close enough.  I mean, when you set that 909 to
> 130bpm, has anyone bothered to see how close it really is?  And yeah, I
> realise that the point of building a timing module like this is so it
> provides master timing for Everything so even if its off everything is off
> by the same amount.
> 
> Anyhow, this is the kinda stuff I lay awake at night thinking about...

Me too, but not that often ;-)  I'd certainly use a microcontroller and 
would probably be setting the frequency/BPM using a set of BCD switches 
(means you need no display.)

If you wanted "fairly good" you could use a decent quality crystal for 
the uC clock.  If you wanted "really good", you could have a 
higher-accuracy timing source firing an interrupt pin, which would then 
drive the counter that does the business.  There are plenty of ovenised 
quartz oscillators on eBay, or you could find a GPS module that puts out 
a GPS-disciplined 1Mhz signal.  (I think that the Trimble Thunderbolt 
has one of these.)

Slightly more down to earth, if a 32,768Hz clock would give you the 
required resolution, you could drive your interrupt pin with something 
like a Dallas DS32KHz, which is a temperature-compensated quartz oscillator.

Cheers

M

-- 
Matthew Smith
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