Low Water Indicator For Coffee Maker Couldn’t Be Simpler


The coffee maker which [Donald Papp] uses every morning has a water reservoir on the back that can last for several days. This means he forgets to check it and from time to time will return to find that nothing has brewed. He decided to add a low-water indicator to the machine. His approach is about as simple as it gets and we admire that accomplishment.

If it were our project we’d probably try to complicate it in one way or another. The use of a microcontroller and ultrasonic rangefinder (like this tank level indicator from a February links post) would be overkill. No, [Donald] boiled down the electronics to a homemade switch, a blinking LED, and a battery. The switch is a flexible piece of metal attached to a plastic cap using some monofilament. The cap goes in the reservoir and floats until the water gets too low, it then pulls on that metal, completing a circuit between the battery and the LED. That’s it, problem solved.

Now he just needs to plumb the coffee maker into a water line and he’ll really be set.

31 thoughts on “Low Water Indicator For Coffee Maker Couldn’t Be Simpler

  1. The simplicity is great! Far more reliable than an overpowered system, and as he said: “it is pretty much impossible to use less power than it does right now” :D

    1. Just use a float, a straw (long stick, whatever) and a small hole drilled in the top, when you can’t see the straw sticking out of the hole refill the reservoir. Now that’s low powered!

      1. Or just get a float valve and never worry about it again as it will self fill the water tank.

        But I like your floating straw idea better. Far more elegant and should have been a part of the design by the coffee maker.

      2. That looks like a pretty deep reservoir, TBH that idea sounds likely to break off and often get in the way, imagine trying to use this underneath a low clearance cabinet or even in-front where the doors are likely to knock stuff.

        Seeing as how this is already an electronic device, tapping into the mains(with an appropriate form of safety and isolation) would be pretty useful, no batteries to change ever!

  2. Needs more arduino ;) simple setup, appears to work fine.

    I mentioned this in the other thread. If hes going to plumb it, just use a floating ball valve and hot gue it in place. that way the water will always be at a constant level

    1. Two raspberry pi’s and a set of lasers and camera boards. use the lasers to illuminate the bottom and cameras to read the diffusion of the water and calculate level. A second one just for redundancy. Then you can make it tweet that the water is low and send you an email with a photo of the water tank, with a sad face.

    1. Simpler vs. easier comes into play, there! The machine pictured has a steel case and an opaque reservoir. Replacing the reservoir with something clear might be one thing but also cutting witness holes or something in the steel casing of the machine… well, a transparent reservoir might be simpler in theory but it’s sometimes *easier* to just make an indicator. :)

  3. Although I gave it up (no palpitations) I wouldn’t want stale exposed to air water in a fresh brew. Serve it up fresh, water included. Holding tank designs are for restaurant use where another batch is an hour away, and you’re busy.
    I still have my curb freebee de-poded Melita cone and filter equipped push-button automatic pumper. Pour your cup of water in, get it back moments later minus a little volume. Best cup I ever made. Fresh.

    1. “Holding tank designs are for restaurant use where another batch is an hour away”

      Ahhh so that’s why every consumer home espresso machine in the world has a holding tank right? ;-)

      Seriously though air contacting water is the least of your problems. Air contacting your beans or your grind on the other hand are far more serious.

      1. We had a water heater that stank at work. I read in Popular Science that if you turn your water heater up to 147 F. it will kill what causes the blacking stink.
        No more stink. Effing experts telling us to turn down heaters to 120F. sucks.
        But at one time I thought of turning it down to just hot enough to wash hands in right out of the separated faucets, it’s in a warehouse. Glad I didn’t. Legionnaires can grow in that environment.
        Home models follow existing design. Home models don’t get thorough cleaning and disinfecting. We had a home model Bunn at work, I worked on it more than once. Looking back at it …YUCK!
        The next killer bug might come from the filthy area behind the faucet of someone who uses tryclosan type antibacterial soaps on just some of their stuff.
        Standing water bugs me weather it is in the bathroom or kitchen. Classic experiment; tap water in glass open to world, examine under microscope. Time. Bugs and plants.
        Home roasting the ultimate machine for sure.

      2. The home brewers don’t have a holding tank with heated water like the restaurant brewers. They have a tank that’s meant to be filled with cold water and used within a day. If you keep water standing in your coffee brewer for weeks you’re doing it wrong.

  4. “Start a brew without enough water to finish it, and your brew is ruined”

    not only that but depending on the quality of the machine you can even ruin the machine.

    cheap coffee makers lack a sensor that may detect the tank is empty and you may burn up the heating element.

    “It uses tiny amounts of power – the CR2023 coin cell used for power will chemically expire before it is ever actually exhausted”

    you can use a lithium cell witch can have a shelf life of years or even better use a current limiting resistor and you can tap into the main power.

    if the coffee maker is one of the better kind that has a pump built in that pumps the water into a 8 ounce heating element it will have some electronics that you can tap into the 5 volt supply and power the led safer

    http://n8tomlin.blogspot.com/2013/02/keurig-disassembly-pics.html shows the insides of the keurig coffee maker and that tin can with the 2 wires going into it in the first 2 pictures is the heating element and i have scrapped out some similar coffee makers and there are 2 sensors (thermister for controlling the electronics and another that shuts off but resets when it cools + usually some thermal fuse that blows if the others fail).

  5. Am I the only one wondering what on earth is going on with the indicator light? I almost feel like there’s got to be some rads getting thrown off on there. Don’t neon indicators do that?

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.