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I'm a newbie here and would really appreciate all kinds of suggestions and answers from the experts here.

I am trying to make a small grey water recycling system project, and for the my primary filtration process tank, I will be using a combination of Metal Sieve and Cloth filter medium. The problem is, I will be making the system alert the user when filters are in need of changing and maintenance. enter image description here

I made a quick sketch of my idea on paint, and as you can see, I am planning to make my grey water collection tank to look that way.

I am thinking of using pressure sensor to sense the change of weight in the sieve and cloth part of the tank for a minimum amount of time so that the system will not confuse water flow weight vs. the weight of the debris on the metal sieve, but I'm thinking that the pressure sensor is not waterproof.

I'm also thinking of like the laser module, and when the light breaks at certain level, meaning there is too much debris that has to be removed. I also googled load cells or weight sensors, but I'm really sorry I'm new to this, I don't know what is the best sensor to use for my problem.

I'm thinking of a float switch a few inches on top of my metal sieve and cloth and when it does not go on a OFF state for a certain amount if time, then the sieve is clogged, but my tank could overflow..

I need something that, when the sieve is clogged, the tank will no longer accept grey water input to avoid overflow. It has to be submersible in water too :'(

Is there a type of sensor that is most suitable for my problem?

Thank you so much everyone. Have a nice day.

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  • I'm confused by your drawing. Where does the grey water enter the system? At the top? – Peter M Oct 26 '20 at 17:13
  • even though this is a very interesting project, it is not related to the Arduino – jsotola Oct 26 '20 at 17:29
  • @jsotola, I'm sorry, how is it not related to Arduino? I will be using Arduino to control everything, the pumps, the stuff that displays on the LCD, the switches and leds. – princessbubbles15 Oct 26 '20 at 17:45
  • @PeterM im sorry, yes the water comes from the top.. and then exits from the hose connected to the pump, which is the blue colored part – princessbubbles15 Oct 26 '20 at 17:47
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    perhaps you could shut off the inflow briefly and weigh the filter – jsotola Oct 26 '20 at 18:18
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I would tackle this not from the point of view of the filter, but from the point of view of the water itself.

The water will be impeded by the filter. As the filter gradually clogs that impediment will increase. The net result will be a slower flow of water through your filter.

There's a number of things you could do to detect that:

  1. Measure the incoming water flow rate and the outgoing water flow rate and calculate the difference.

This would mean having all the water flowing through two flow meters which would complicate your design as the filter will no longer be able to deposit directly into the tank. But when the difference in flow between the in and out sensors gets above a certain point (to be determined by you) then you can safely say that the filter is blocked.

  1. Measure the "backlog" of water. To do this the input portion of the filter will have to be sealed (or largely sealed). Again the filter will impede water flow, and the more it's clogged the more it impedes. Once the impediment becomes too high the water will start "backing up" up the input pipe as it can't get through the filter fast enough. At this time you can detect that rise in water level with a float switch.

You'd have a simpler design now, as the filter can deposit straight into the tank. Whether you want to detect the rise in water level in the incoming pipe itself or in the gap between the filter and where the pipe comes in depends largely on the size of your filter. With a large filter it may be better to have a smaller space at the top and measure in the pipe. That will "amplify" the level rise and make it easier to detect.

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  • "The net result will be a slower flow of water through your filter." Actually, IIRC, the result of constricting the area that water flows through will increase its speed but decrease its pressure. en.wikipedia.org/wiki/Bernoulli%27s_principle – nick012000 Oct 27 '20 at 5:14
  • @nick012000 I do electronics, not fluid dynamics. All I know is when my sink gets blocked it backs up and takes longer to empty. What mechanics that's due to I neither know nor care about, but it does happen. I can prove it. – Majenko♦ Oct 27 '20 at 11:09
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Have you considered a Differential Pressure Sensor, They can be gotten for a few dollars complete with the basic electronics and drift compensation on board. Try looking for: nxp pressure sensor for a start. These will interface to the Arduino A/D. I use an absolute one for barometric pressure and a differential to measure the air pressure my fish pond, this tells me if the air line is open or broken.

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  • You could probably improve this answer by discussing Bernoulli's Principle and explaining why there's a drop in pressure. – nick012000 Oct 27 '20 at 5:16
  • I am measuring differential pressure not flow. That is a common method of measuring filters to determine when they are due to be changed and or cleaned. The Metal Sieve and Cloth filter medium is the filter. – Gil Oct 28 '20 at 16:28
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It seems to me what you want to detect is when the filter starts backing up and the flow of water out of the filter can't keep up with the in-flow. That will let you turn off the in-flow before the tank overflows.

So put a float switch or other level sensing switch on the space above the filter. Set it so it trips when the water standing on top of the filter gets close to the top of the tank. If the filter gets clogged and the water can't flow through fast enough, the water level on top of the filter will start to rise, and when it gets high enough, the level sensor will trip and your Arduino can shut off the flow of gray water into the filter tank.

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