> You may get precise time signals from "radiostations > of precise time signals" for example. Here in the states there are receivers that receive a signal of 60 KHz directly that are usd to keep/correct time. Of course, GPS is another obvious choice for either correct time or time correction (using 1 Hz time "pulses" from receiver). As Mike pointed out, keeping simple un-ovenized, free-running crystal oscillaters "on-frequency" is a considerable design task itself. (Each and every crystal exhibits slightly different characteristics over temperature and time that MUST be offset in a variety of ways - not to mention requirements for periodic calibration at say, yearly intervals, that are meant correct for component and crystal aging.) RF Jim ----- Original Message ----- From: "Mike Singer" To: Sent: Monday, August 12, 2002 7:36 AM Subject: Re: [OT]: What Test Gear to measure xtal frequency to 1Hz > Peter Crowcroft wrote: > . > . > > We are using a 12.000MHz crystal in a timer circuit. It has 2 > > x 33pF load capacitors and the xtal is under the IC socket > > so the tracks to the uC are 0.15" only. > > We want to measure the osc frequency to within 1Hz so we can > > adjust the load cap in one leg. Can someone tell us what test > > gear we need to be able to do this? > . > . > Peter, > given your "12.000MHz crystal in a timer circuit" capable > of keeping 1Hz stably, you need nothing more, but > precision timer or clock, I think. > Count your timer ticks for a long enough precise time > period and you'll get the osc frequency. > Then you may use one of your so precalibrated timer > circuits to fill periods of next your timers in order to > speed up measuring process. > You may get precise time signals from "radiostations of > precise time signals" for example. > Keeping 1Hz stably at 12.000MHz crystal is not a simple > task. look at Microchip's DS00588B.PDF. > > Mike. > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.