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Free Idea: Smart Home and Water Softeners

You may remember that some years ago I had a water softener installed, and I can report I’m very happy with it. The one part that has been a bit more annoying is that there is no obvious reminder when it’s time to go ahead and put in new salt blocks — most softener use some version of salt, the one I’m using uses 4Kg blocks as the preferred method, though you could use tablets as well. Since the consumption of the salt depend both on the hardness of the water supply and how much water we consume (which in turn depends on how much time we spend at home), it’s hard to put a hard and fast rule of how often to go and put the salt in.

And, because things are widely different in different parts of the world, I need to point out that I’m talking about a twin-tank water softener that is about the size of an early ’00s PC chassis, not the large tank the size of an immersion heater boiler that is commonly used in parts of the world (such as the USA) where space is not at as much of a premium as it is in a dense city like London. I would put a picture but the one company that has a clear picture of the sizing is the one company that ticket me the wrong way when I was looking to get one installed, and I don’t want to bring them more customers.

Anyway, the two blocks of salt fit in the front of this “chassis”, and they are consumed from the bottom, where they lay in the water. I was originally worried about dust and other contaminants around the device, but it turns out this is not the same water that is put in the loop, it’s only used to handle the process that undoes the limescale built up in the softener’s tanks.

To try to measure whether you need to put in new salt, you don’t measure the water level, but you rather measure the height of the block of salt: once it goes below a certain level you can “queue up” the next block on top of it. But when I thought how to do this, I realized that the most obvious ways (drill a hole on the cover, use a time-of-flight sensor) would not work for me, since I’m leasing the softener (as I’m also renting the flat, it didn’t make sense to buy the softener, as we might need to move out and not be able to set it up again after we move.)

The second best thing I can think of is to use load cells: since the softener is (for physical reasons) on top of a shelf, and we do not leave anything on top of it, the weight of its combined system is almost entirely affected by the blocks of salt themselves. Unfortunately I don’t believe this is going to be as simple as getting two load cells and setting a threshold, as I expect the sensor to be very noisy, not just for the times we would go and much around the softener, but also because my understanding of the cleaning cycle is that it loads and then discharges water, making the overall weight of the system quite variable.

Thus, my general idea of how to handle this is to put two load cells under the front of the softener (and a matching spacer on the back, as the device needs to stay level to operate), and measure for an extended amount of time to best decide what formula to apply to the readings: I somehow don’t expect that a five minutes average is particularly helpful, but neither is the 95th percentile. I guess to actually know what to use I would need data and experimentation, and I have yet to do that.

Part of it is the lack of time, but also in part a bit of analysis paralysis: in the closet my softener is I don’t have easy access to power. For the windows’ motor, I actually draw the power from the motor itself (it’s designed for it, for external controls), but I don’t want to use the same power supply to read the load cells. I have been thinking of playing around with supporting rechargeable cells (16850 most likely) in my acrylic lamp board for the sake of experimenting and re-using for this particular project (as well as my Tetris fix), but I have not gotten anywhere close to get anything ordered.

Practically speaking, the easiest option to start with is using a 20Ah USB powerbank, as it should last plenty for at least the experimental recording to figure out whether this is even a feasible option. After all why expend more energy and money on a project that might not even work at all? But there is another option here that I’m interested in considering: using a Bosch drill battery.

The reason why I’m thinking of that is that I have a battery-operated Bosch drill – yes I know it’s not as trendy as Makita nowadays, but I’m old school, don’t hold it against me – and I rarely ever use it. But giving batteries I already own a good use sounds like a generally good plan. But this again is something I have not explored, though I would really appreciate it if someone wanted to try — or point me in the direction of someone who already did.

Comments 2
  1. Being in the US, I’ve been thinking about this for awhile. My plan was a distance sensor that would send me an alert when the level gets low. I already bought the ultrasonic distance sensor, I just need to get around to writing up something for one of my CHIP computers and figure out a way to clip it to the top of the salt chamber. It’s a little easier for me since the storage chamber for the salt is just a big tub with a plastic lid, I can hang something on the lip.

    Maybe this will be the push I need, lol!

  2. Do you need to measure it, or just know when it’s time to add salt?
    Set up a horizontal laser, and photoresistor. Then have a microcontroller wake up once an hour to shoot a short blip, to see if there’s a salt block still in the way.

    I dunno, I’m sure there are better ways. Hell, have a physical switch close by salt no longer blocking it, powering a circuit that transmits right then. Zero battery use while there’s enough salt.

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