How about doing the correction in software based on measured temperature and a look-up table? This seems a lot less power hungry than a crystal oven. Harold On Tue, 10 Feb 1998 20:52:23 +1300 Russell McMahon writes: >Observation reveals that, if you trim a digital wrist watch >crystal oscillator carefully you can get long term >accuracies of well under 1 second per day drift. This is a >low cost 32 KHz crystal which hasn't been chosen for its >precision! This is a lot better than the specifications for >the crystal that the manufacturer would claim. Importantly, >even if it drifts, my experience is that it drifts >consistently and in the same direction. Of course, in a >professional design you are obliged to do a worst case >calculation based on the manufacturer's worst case specs >:-). The watch has the advantage of being attached to a very >good "oven" (your wrist, maintained at about 98 degrees F). >An article for a "micropower crystal oven" appears in >Electronics and Wireless World, August 1997 page 660. The >circuit uses 2 '555 oscillators which apply a variable mark >space signal to a heater resistor with the overall mark >space being controlled by feedback from an NTC thermistor >located with the crystal in the "oven" compartment. Power >consumption is not specified but can be minimised by running >the oven at "just" higher than the highest external >temperature liable to be experienced. More insulation will >require less wattage (and produce a slower thermal >response). > _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]