Check frequency
in [Basics]
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From: Jasen Betts on 17 Dec 2009 02:29 On 2009-12-16, ClueLess <clueless(a)wilderness.org.invalid> wrote: > Hi all > > I have a requirement to exactly adjust the frequency of a > microcontroller system (8051) that works with the 32768 Hz watch > crystal. > > I am not an electronics engineer but a hobby type. I will thank you to > please let me know how the system can made to work exactly at the > above frequency. Trimmers are provided. my understanding is that you > need an oscilloscope to do this. In that case what kind should I go > for? Os is there a simpler methods? Set the device up to count cycles between input pulses and feed it the 1 Hz pulse train from a GPS, trim until you get close enough to 32768
From: Phil Allison on 17 Dec 2009 03:21 "Jasen Betts" <jasen(a)xnet.co.nz> ** Sheep shagger extraordinaire. > Set the device up to count cycles between input pulses and feed it the > 1 Hz pulse train from a GPS, trim until you get close enough to 32768 ** The crystal will be 32.768 kHz out of the box. Idiot. ..... Phil
From: John Fields on 17 Dec 2009 14:41 On Thu, 17 Dec 2009 12:58:38 +1100, "Phil Allison" <phil_a(a)tpg.com.au> wrote: > >"John Fields" > >> For this application an oscilloscope will be useless and you should use >> a frequency counter. > > >** Shame how even the cheapest DSOs have built in frequency measurement to >5 decimal places. > --- Shame how analog scopes, which is (since he didn't say "DSO") what he was talking about, don't. JF
From: John Fields on 17 Dec 2009 14:52 On Thu, 17 Dec 2009 19:21:12 +1100, "Phil Allison" <phil_a(a)tpg.com.au> wrote: > >"Jasen Betts" <jasen(a)xnet.co.nz> > >** Sheep shagger extraordinaire. > > >> Set the device up to count cycles between input pulses and feed it the >> 1 Hz pulse train from a GPS, trim until you get close enough to 32768 > > >** The crystal will be 32.768 kHz out of the box. --- Actually, out of the box it'll be a little high. --- > Idiot. --- A dog smells his own farts first, yes? JF
From: John Fields on 17 Dec 2009 15:09
On Thu, 17 Dec 2009 13:26:31 +1100, "Phil Allison" <phil_a(a)tpg.com.au> wrote: > >"ClueLess >> >> I have a requirement to exactly adjust the frequency of a >> microcontroller system (8051) that works with the 32768 Hz watch >> crystal. >> >> I am not an electronics engineer but a hobby type. I will thank you to >> please let me know how the system can made to work exactly at the >> above frequency. Trimmers are provided. my understanding is that you >> need an oscilloscope to do this. In that case what kind should I go >> for? Os is there a simpler methods? > > >** To get the frequency exact, you need resolution better than 1 Hz --- I don't think so. If you've got a 32768 Hz crystal in an oscillator and you want to measure the output frequency to an accuracy of, say, +/- one part in 32768, then if you use a 1 second timebase to accumulate cycles it has to have a resolution of +/- 30.51757... �s --- > -one >way is to use a frequency counter that can be set to count for 10 seconds - >giving you 327 thousand odd counts on the display. --- True. --- >Picking up a signal voltage from the crystal without disturbing it is a >problem too - most counters would stop the oscillations if directly >connected. --- Using a 10 megohm scope probe to connect the counter to the driven side of the crystal, IME, won't stop it, but it will pull it. --- >Time for a Reality check: > >Just how " exact " do you really need it ?? > >A watch crystal will be within about 30ppm (or 1 Hz ) with no adjustment. > >To get better accuracy, you will need at a dual trace scope and a quartz >clock that keeps good time. > >Dunno why you are playing with uPs when you have no scope. > > >.... Phil > > JF |