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Float Sensor – where do the wires go June 8, 2010

Posted by rik94566 in aquaponics, arduino, Float Sensor.
Tags: , , , ,

Out of the box the float sensor comes with only 2 wires out the bottom.  My thoughts are that I need 3 wires to get the thing to work correctly.  Not only does the sensor only have 2 wires, but they are both black.   Most sensors I have  ordered or used in the past have always had a red and black wire to work with.  Such is electronics, never what you think it should be.  Not much documentation to help figure this wire situation out either.  I do know from the Instructable by Luke Iseman for the Garduino his sensors only use 2 wires.  Luke was also featured in Make: magazine’s ReMake America volume 18.     

Here is the link to this great project:      


If you look at step 4 this is where he does work with the media probe that he constructed.  You can look at the electrical drawing and figure it out.  I always have a hard time with these as I am new to electronics.  My background is horticulture not electronics.  I can read enough to see that he uses a 10K ohm resistor (1/4 watt will be fine) between ground (BLACK) and the signal (YELLOW) wire.  Good enough for me.  So I will work that into my working model.  You can get the resistor at Radio Shack for .99 cents.      


Here is how I wired up the float sensor to the terminal block on the base unit.      

Sensor wires to Terminal Block

Not knowing which black wire to use for which screw set, I just put them in the way I wanted and tested the results.  Then I switched them and tested again.  I could not tell any difference either way.  So any way you do it is right.  Knowing I needed the 10K resistor I put that in the location shown above.  This is IMPORTANT to get right. I connected one end of the resistor in the bottom terminal connector and then ran it to the middle terminal connector.  I then took one of the Black wires from the float sensor and placed it in the middle terminal connector.  The final connection was to place the unconnected Black wire from the float sensor to the upper terminal connector.  Then I was done with this task.  In the picture you can see that the bottom terminal connector only has a resistor in the connection.  That is because the other side will be where the Arduino ground wire will be placed (BLACK wire).   You can place either end of the resistor where you want them.  It does not matter as resistors restrict the flow of electrons both ways.   Make sure all screw connections are tight or the wires will fall out and you will be doing this again.   

Real application configuration

 Terminal blocks are not used in aquaponic tanks or grow beds.  So we need to see what this will look like in real situations.  The full directions on the connections are below.   

First connect a resistor to the BLACK wire (GND), next connect the YELLOW wire (COM) to either of the Float Sensor black wires, now connect the other Float Sensor black wire to the RED wire (VCC).  Next take the un-connected resistor end and connect to the YELLOW wire & black Float Sensor wire.  You are now wired up and ready to go.     

To make this water tight you will need to use heat shrink tubing over the connections.  If you do not know how to do that ask a friend or check the internet.  You can get heat shrink tubing at Radio Shack also.    It is also a good idea to solder all the connections.  I will be doing an Instructable about how to get the float sensor working and will put a step in to cover the heat shrink thing for everyone.  Right now not important.

Connection to Arduino from Terminal Block

 I am using a ScrewShield to demonstrate the connections better for you.  You can just stick the wire ends in to the correct pins and it will work just fine.  Make sure the wires are stripped of insulation before inserting them into the pins or terminal connectors.   

Connect BLACK wire into the GND pin.  Connect the RED wire into the 5V pin.  Next connect YELLOW wire  into the Analog 0 (zero) pin.  You are now wired up and ready to work with the sensor.   

When completed the connections will look like the picture below:   

Completed Connections



1. Eric - June 9, 2010

It’s a switch activated when water reaches certain level. You would need ultra sonic or other sensor if you want to know current water level.

The link in Garduino is a moisture sensor, maybe not the same purpose?

rik94566 - June 9, 2010

Thanks for pointing out this is a float switch and not a float sensor. It makes total sense to me now. You are right in the fact the float will only activate at a certain level that is good information. That is ok; because that is really I want it to do. I was using the Garduino case to show that I needed a resistor in the circuit. The Garduino moisture probe is being used for the same purpose as I am using the float switch for. It turns a water pump on and off. Once I get to a more advanced level I want to play around and learn how I could use the ultra sonic sensor you are talking about. Thanks so much for your help on this.


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