[RETROFIT]: Detecting position of a dial

Hello Internet!

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My parents have an old dishwasher at our summer house of which recently broke its mechanism that stops the washing when completed. Everything else works perfectly and they cannot find the part anywhere they looked so they asked me to find a new one to suggest them to purchase. This goes way beyond my life theory. There is no way I will allow this to happen for something that stupid! I hope you understand my logic. I’m a maker not a stupid consumer.
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So let me go straight to the point. I want to interefere the least possible with the dishwasher, aka I don’t want to open it and try to unerstand much of its internals. There is a dial that completes 1 single spin like a clock of 360 degrees. Starts at pointing up (like 12:00 in clocks) and ends at the exact same spot once the cycle is completed. I have attached an image of something fairly similar. So my idea was to detect that exact positioning and take action probably in the form of a relay cutting mains supply to the dishwasher which is all is required.
My question to you is if you have any “method” to suggest. I am thinking of attaching some sort of metal conductors on both the moving dial and the body of the washer that will touch (hopefully precisely enough) and arduino will sense that to take action. I read hall sensors paired with a magnet are really not accurate at all. We are looking for a +/-1mm precision here or less.

So squeeze your minds and suggest me what you think will do the work please.

Thank you in advance

Well, if you're really a maker, then it should be no trouble to open the thing up and find the broken part.

Hall sensors are extraordinarily accurate. The real challenge is mounting it securely enough that just handling the knob doesn't bump the calibration.

What about just using a timer to switch the thing off. Start the timer when the wash program is started and then the timer cuts off power say 5 minutes after the normal end of the wash cycle?

...R

Robin2:
What about just using a timer to switch the thing off. Start the timer when the wash program is started and then the timer cuts off power say 5 minutes after the normal end of the wash cycle?

…R

The actual part that is broken inside it is replaced by a “professional” with a simple push button. I don’t have that broken part anymore. And this is where the real problem is. The push button does not get depressed once the cycle is completed so it continues from the beginning and once the water is in again you need to wait for the second cycle to continue :slight_smile:
About the timer, unfortunately as the dishwasher warms up the cold water, this is something that I cannot predict its duration hence the total time of the cycle varies and I need to stop it right on the correct spot.
:S