A float switch is a device which detects a fluid level (such as water) and activates a set of contacts which may be further integrated to a control circuit for restricting the fluid flow behavior.

Why a Float Switch


The advantage of a float switch is that it works without a direct contact with the water making the procedure free from all sorts corrosion or mechanical degradation problems,

I have discussed a host of different water level controller circuits in this blog, however all have incorporated a direct contact with water for sensing the levels and for activating the connected control circuits.

It means all the previous circuits could be vulnerable to a long term degradation due to corrosion or oxidation effects.

The present design helps to tackle this issue by describing a non-contact water sensing technique through a float switch mechanism.

The Concept


The idea is actually very simple, here we have a plastic pipe which has a sealed reed switch positioned somewhere within its length where the intended sensing may be required and a plastic ring carrying a permanent magnet secured around the plastic pipe such that the ring slides across the entire length of the pipe freely.

The sliding action of the ring around the pipe should easily take place with the water pressure, meaning the pipe ring must be light enough and should rise or fall in response to the water level conditions, in other words it should float in water, clinging to the pipe since it's secured around the pipe (the pipe running through the center of the ring).

Construction Details


The materials that would be required for making the proposed float switch circuit are as given under:

  • 1 inch diameter PVC pipe, length depending upon the water tank depth or as per the user parameter.

  • A suitable plastic ring (1 inch thick) having a central hole diameter slightly more than the outer diameter of the pipe.

  • A reed switch, quantity will depend on the type of water level sensing application.

  • 1 mm dia enamelled copper wire, 5 meters approximately or more depending on the tank depth.

  • Epoxy seal, for sealing and securing the outer wire terminals from the pipe and to make the pipe water tight.

The image below shows  a typical reed switch unit. As can be seen it's a tiny (not more than an inch long) glass encapsulated device which encloses a pair of ferromagnetic ( such as iron) open contacts, while the outer terminals being made up of a non-magnetic metal such as copper or brass.

The inner contacts being responsive to a magnetic field, instantly reacts to a magnetic field or lines of magnetic flux when bought at a relatively close proximity resulting in closing of its internal contacts which causes a short or a connectivity across the outer leads.



We use the above explained reed switch in the pipe for detecting the water level conditions via the magnetic ring float either for activating its contacts or vice versa.

Procedure for making a home made float switch device


As shown in the figure below, the length of the super enameled copper wire is appropriately measured and soldered with the reed switch ends as indicated in the diagram below.

The wire ends are sealed with epoxy sealant at the mouth of the pipe so that the pipe becomes watertight and also the wire ends get tightly secured. The free ends must be cleaned, tinned with solder and used for further integration with the control circuit.

In the figure below, the assembly suits a tank overflow controller system since the reed switch is positioned at the top of the pipe, near the brim of the tank, similarly more number of such reed assemblies could be used across the different lengths of the pipe for getting the reading and control over the relevant levels of water.

The Design Set up




Making the plastic float could be a little complex, as it will require a thick plastic piece to be fabricated such that it consists a hole which is just enough to the pass the plastic pipe smoothly and freely through it.

The upper/inner rim of this plastic float must allow a magnet insertion, this could be done either by drilling a vertical hole through it and snug fit a rod shaped magnet, or make a U shape slot over the upper surface of the float and embed an identically dimensioned U shaped magnet over it.

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