[time-nuts] Car Clock drift - the lowly 32kHz tuning fork

Morris Odell vilgotch at bigpond.net.au
Tue Apr 11 03:21:40 EDT 2017

> Most wristwatches do not have any temperature compensation. If worn, the wristwatch is pretty close at the 25°C (the human body is a quite good and temperature stable oven). The difference only starts to > show when the watch isn't worn for long periods of time.

That explains my experience with the first microcontroller based clock I built years ago. I used a commercial module with a micro and some accessories including a watch crystal for timing. It's on a window ledge facing west in Australia where the temp varies during the year by 40°C. It was always a bit fast and I spent a lot of time checking my code to make sure I was dividing it by the right amount. I eventually tamed it by programming a short pause at 3:00 am. I'm sure the temp of the watch crystal is very rarely 25°C!!


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