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My dream device is a way to quickly make tea. I can use most of the parts from a Mr. Coffee tea maker but the last part is a way to start the flow of water, measure say, 1/2 a gallon and then stop the flow. It can't be hard . . . ice makers do it all the time. How does an ice maker do it?

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  • \$\begingroup\$ Ice makers measure the amount of ice in the ice bucket, not the amount of water used. Is there an analogy for your device? \$\endgroup\$ Mar 23 '11 at 1:04
  • \$\begingroup\$ The ice maker in my freezer appears to use bucket level to decide its ok to empty the tray of frozen cubes, and a timer to control the amount of water to fill the tray knowing that the volume won't vary by much as long as the orifice is relatively constant in size. \$\endgroup\$
    – RBerteig
    Mar 23 '11 at 7:57
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    \$\begingroup\$ Not the ice bucket . . . the part BEFORE it goes in the ice bucket. From what I can tell it looks like it adds a certain amount of water and doesn't have a "full tray" indicator. \$\endgroup\$
    – tooshel
    Mar 23 '11 at 16:56
  • \$\begingroup\$ Check out this tutorial for an arduino flow meter : diyhacking.com/measure-water-flow-rate-and-quantity-arduino \$\endgroup\$
    – user43266
    May 22 '14 at 15:39
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I'd use a load cell to measure the weight of the container, and turn off the water flow when the contents reach half a gallon.

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  • \$\begingroup\$ I thought about something like that but I wanted to keep the "logic" simple. If I measure the weight then when I want to "make tea" I have to call for water, wait for the weight, turn off water, start brew process or something like that, whereas if I could measure 1/2 a gallon it could start adding water and start the brew process at the same time. \$\endgroup\$
    – tooshel
    Mar 23 '11 at 17:00
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    \$\begingroup\$ What's to stop you starting the heat as soon as there is enough water to prevent overheating, and continue to poll the load cell? (I think a timed inflow would serve just as well, but the concept is the same in either case). \$\endgroup\$
    – JRobert
    Mar 23 '11 at 18:31
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Some coffee machines detect water level using a magnetic float inside the glass/plastic tank and a hall-effect sensor outside it.

Hobbyist supplier futurlec.com has in interesting-looking range of flow sensors, also.

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You might consider an ultrasonic flow meter.

But, I'd either use a calibrated timer or prefill a chamber of known volume on demand (using a sensor to show when it's full), then empty the chamber into the cup.

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    \$\begingroup\$ A flow meter will be less accurate than a measurement of volume; it will suffer from the same problems you'll get when trying to do dead-reconing with an accelerometer. \$\endgroup\$ Mar 23 '11 at 1:03
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    \$\begingroup\$ Using a holding tank to pre-measure a volume of water is the way that commercial coffee makers such as those found in offices work. \$\endgroup\$
    – longneck
    Mar 24 '11 at 0:53
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Put the vessel that is receiving the hot water on a sprung base, and attach a microswitch to the base that is pressed down as the vessel fills with water that cuts the power to the pump (or heater if your using steam pressure to transfer the water) when the base is pushed down far enough.

You'll have to fiddle around with the sprung base and switch to get it to trip at the moment that it has been filled to the desired level.

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Cheap appliances typically use a water regulator and a timer. Some water inlet valves include the pressure regulator, so you can buy one part and get both the regulator to give you a consistent flow, and a solenoid to turn the flow on and off.

You could try one similar to this.

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Most appliances use timers or level switches as mentioned before. To answer your specific question, you can use one of these.

I haven't tried one yet, but the price is so low (flow sensors tend to be expensive!!) I can't resist.

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Proteus Industries makes electronic flow meters. They came to mind because I once helped swap one out in a high powered laser exciter; one was used to detect if the flow of water cooling the system was inadequate, and would shut down power.

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