Pedro had a problem with his Venta Humidifier, although it has a nice "discrete" design it lacks one important feature: an external water level indicator. Pedro drafted a small specification of what he wanted, two indicators, one for "almost empty" and another for "empty", if possible when empty stop the motor i.e. cut the power.
I checked the price of a new one (just in case I ruined it beyond recognition) and after taking note of the 114€ price (and they weren't able to add a simple level indicator... shame on you product designers), I went to work.
My first idea was to use a buoy and a lever to externally indicate the level, but it appeared to be too fragile to store and to align the top of the Humidifier, then I though of building a buoy with a magnet and placing Reed switches on the outside of the case.
Having a small tube glued inside was very easy, I had to use hot glue as special PVC glue (in the picture) did not work with the case (clearly not PVC!!).
My original magnet was too heavy, it weighted about 7g and for that I needed about 7cm² of foam supporting it, too much!Then I tried 3 and 4 smaller magnets, about 1g each. Here is a picture of the magnet with the floater and the REED switch on top.
After having the level system I went out to design the electrical system. Initially I planed on using a normally closed reed switch for the power but a switch capable of cutting 230V 0.35A inductive load is impossible to find.
So I had to resort to an additional battery and a relay to invert the signal, the use of the battery made me use an extra power switch to turn off the detection circuit when the Humidifier is stored away.
Two normally open switches, one lighting a green LED when the level is almost at the bottom and a red LED lighting when the level of water is at the bottom and cutting the motor when this happens. The Relay contact is normally closed so that if the battery runs out or Pedro doesn't want it to operate just remove the battery and let it work as previous.
Here's is the finished "product", with the boxed closed and the LED visible.
Here's another picture, just to show the chaos during the creative process... :-)
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