Power line timebase

[Michael]

Yeah, I thought on the secondary side the noise level would be down quite a bit...plus just a simple 1N4003 in series with a good resistance 10k, 47k something like that. Some high freq filtering perhaps.

I'll look at it on a scope and create some noise myself....grab my power drill or something.

I think only something like a refrig would be a problem and it would depend on it's design as well.....and if it was on the same circuit.

For you real software gurus, I suppose I could maybe even just look for the 1 second during a shorter window of time? (and ignore everything else)?

...Hmmm

[Michael]

That didn't make sense...getting carried away.

It's the count that could get corrupt, so "when" I read it wouldn't make a difference.

(I have to be careful with this brain of mine...it's a loose cannon).

[skimask]

Yeah, I thought on the secondary side the noise level would be down quite a bit...plus just a simple 1N4003 in series with a good resistance 10k, 47k something like that. Some high freq filtering perhaps.

I'll look at it on a scope and create some noise myself....grab my power drill or something.

I think only something like a refrig would be a problem and it would depend on it's design as well.....and if it was on the same circuit.

For you real software gurus, I suppose I could maybe even just look for the 1 second during a shorter window of time? (and ignore everything else)?

...Hmmm

Why not combine old and new technologies for a solid timebase.

Have a PIC triggered off the mains freq, and to keep it from false-triggering due to a fridge kicking in or something, have the PIC wait at least 16ms (at 60hz) before it'll even think about accepting a new trigger...or something along those lines...

[Ingvar]

I suspect that the worst possible things would be old refridgerators and heaters(radiators) with mechanical thermostats. Loads of contactbounces. I remeber having problems with our fridge and it wasn't even on the same phase.

Digital filtering like Skimask suggests would improve but never get rid of the problem completley. Your clock will always be "fast" unless you do this right.

I also remeber that the mainsfrequency was considerably lower during daytime and higher at nighttime. The electrical producers compensated for the high load at daytime by increasing frequency at night. Over a 24 hour timeperiod there should be almost no error atall. Thought i'd mention it since you didn't like drift due to temperature.

You also have the option of a temperaturecompensated oscillator, Dallas(now Maxim) makes many but this one should probably be good enough ..... http://datasheets.maxim-ic.com/en/ds...z-DS32KHZS.pdf
...... not cheap but it solves most timekeeping problems.