On Tue, 02 Jun 2009 06:07:28 +1000, Bob Larter
wrote:

wrote:
On Tue, 02 Jun 2009 02:03:46 +1000, Bob Larter
wrote:

Sylvia Else wrote:
Don Klipstein wrote:

Cheaper still requires oscillators regulated by component tolerances
- and oscillators tend to have at least two components affecting
frequency, and finest tolerance of ones easily available at premium
prices is 1%, meaning low chance of achieving timing highly reliably
better than 2% in either direction unless either crystal or power line
time base is used.
I'd have thought getting the cycle to within 10% would be more than
adequate.
It would be. Washing machines used to use synchronous motors driving a
cam, which was far more accurate than necessary to do the job properly.

Failure of mechanical timers on appliances is VERY common, and usually
results in the appliance going to the landfill.

Sure, but it was the cam/switches that would fail, not the motor.


Oh, I've seen plenty with a motor that stopped. Regardless, mechanical
timers are a glaring weak spot in appliances.

Electronic controls, done properly, are far more reliable.

In theory, sure.

Yes, there
are some that are done properly!

I'm sure that there are, it's just that I haven't run into any.

Take a look at a Fisher & Paykel. When they designed it, they started
with a clean sheet of paper. They didn't just slap a few blinking
lights on a conventional washing machine.