Hello ! English is not my first language so sorry if i make mistakes. I was wondering about the kind of clock inside washing machines when you set a program for later, mine allows me to chose between a delay of 3h, 6h and 9h by pushing a switch and there’s no screen. What’s the most efficient way to build it ?
In: Engineering
I’ve seen two reply’s that explain an oscillator based clock. This is one way to solve it, but it’s too difficult to pull off efficiently and cheaply for most applications. Things that only need to get time _kinda_ right like microwave ovens or your washing machine use a different trick.
Mains power is alternating current, that switches direction (or the polarity of voltage) 50 or 60 times a second (depending on your country). The microcontroller in your device counts these oscillations as a way to keep track of time. A skilled engineer can even pull it off without a microcontroller at all, which saves a whole lot of development time and money.
The only problem with this method is, that mains power only oscillates with _kind of_ 50 or 60 Hertz, which means that it is not uncommon for these clocks to be off by a few seconds or sometimes even minutes in a matter of weeks. That’s why you might need to adjust that damn microwave clock every few months or so.
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