About 20 years ago, a friend of mine came to me saying that he had to repair a customer’s  water level control made out of electromechanical relays which was falling apart.  He understood that the original control relied on conductivity of water. The customer didn’t want any type of float switch so he had to stick to the way it was meant to work.

He could start the pump whenever water fell below the “low” level electrode and pump would stop once it reached the “high” level electrode but, as water was consumed and its level barely dropped just below “high”, his circuit would re-start the pump just to stop it as soon as “high” electrode was touched by water again. This process kept going on and on until he switched power off. His circuit was oscillating which was not good for a 5 HP water pump or any pump at all.

He needed help. At this point I asked him that instead of working with relays, wouldn’t it be nice if the control were electronic which would probably be less expensive, more reliable and have a longer life?

 I intended to build a kit for Club Jameco out of how I remembered this control worked and this is what this instructable is all about. 

*** Disclaimer: This kit is meant to operate with equipment such as line operated water pumps or motor starter relays and/or contactors at lower control voltages. Line voltage is dangerous and if mishandled can cause injury or death. If you are not familiar or have not worked with line operated equipment, have a licensed electrician do the power wiring for you. This kit is meant to be educational in nature and can be used with line operated equipment if National Electric Code guidelines are followed. ***

Step 1: Proposed Control Slide Show

The slide show included in this instructable shows the basic operating theory behind this control. It assumes that the pump is a small plug-in pump. This control has a small 12V coil relay whose contacts are rated at 10A 120V. You can select any relay to suit your water pump's power source.

Step 2: Suggested Circuits for Bigger Pumps.

120Vac Pumps

The first schematic shows how to adapt the water level control to bigger pumps still rated at 120Vac. You would have to get a Power Relay part number AD-PR40-1C-120A from Automation Direct dot com. This is a SPDT (Single Pole Double Throw) relay, which means it has only two sets of contacts and three terminals for one line only. One set of contacts is NO (Normally Open) and the other one is NC (Normally Closed) with one terminal common to both. The circuit shows the Normally Open contact.


This Power Relay coil is rated at 120Vac so our controller will be able to switch it on/off safely. The contacts of this Power relay are rated at 40A 300Vac. This is more than enough for pumps up to 1HP at this voltage.

240V Pumps

To switch on 240Vac pumps, you would need a relay with two sets of contacts such as Automation Direct Part Number AD-PR40-2A-120A. This relay’s coil is also rated at 120Vac so our water level control can switch it on/off at rated voltage. The second schematic shows how a pump up to 2HP can be wired for proper operation.


These relays should be placed in an enclosure for safety.

Step 3: The Schematic

This schematic was originally drawn using CadSoft EAGLE software for PCB design.  As it seemed hard to read it has been modified for clarity.  A small step-down 120Vac:12Vac transformer rated at 250mA feeds the on-board power supply through terminals X1-1 and X1-2. The transformer provides the low voltage required for the control plus galvanic isolation between control circuitry and the mains. In order to keep parts number at a minimum, a CMOS CD4001 circuit was used so only one supply voltage is needed for both, control circuitry and relay.

In addition to what was shown in the slide show, this control circuit includes two LEDs, one green LED to show when pump is running and a red LED to show when control is in pump protect mode. The green LED comes on every time the relay comes on. This LED –and its current limiter resistor- is in parallel with the coil of the relay. If red LED is on, pump and green LED will stay off even if pump is required to come on. Once red LED goes out then pump and green LED may come on if needed. 

The circuit formed by transistors Q1 and Q2 is designed to turn on the red LED (Pump Protect) whenever there is no water between pump protect electrode and ground electrode at pump reservoir. Q1 comes on as soon as water level drops below pump protect. Q1 base current is too small, less than 1 micro Amp. Q1 and Q2 are wired as a Darlington pair so Q2 can turn on the red LED when required.  Once there is water between pump protect and ground electrodes, Q1 turns off causing red LED to go out.

IC1-B gate works sort of an AND gate. This means, whenever main tank needs to be filled up and pump protect is false, this gate turns on transistor Q3 which will turn on the water pump.


Step 4: The Printed Circuit Board

I like designing electronic gadgets as a hobby. However, any time I had to build one, I did it with general purpose prototyping boards using the point-to-point soldering technique.

I had never done any PCB before, so, I had to learn how to make my own. I learned from this instructable:


Eagle files for this controller are included in this step. By the way, the PCB shown in this instructable is the first PCB I ever made.

When etching time came, I chose what looked to me as an environmentally friendly method, see:


If building your own PCB or doing point to point soldering on prototyping boards is not your thing, you can click on the following link to buy this water level control as a kit from Jameco which includes everything you need except the transformer:


Step 5: Parts List



3x - 2.2M ohm 1/4W (R1, R2, R3)

1x - 4.7K ohm 1/4W (R4)

1x - 120K ohm 1/4W (R5)

2x - 470 ohm 1/2W (R6, R7)

1x - 15K ohm 1/4W (R8)



1x - 330uF 63V (C1)

1x - 220uF 25V (C2)

1x - 1uF 63V (C3)



5x - 1N4004 (D1, D2, D3, D4, D5)

1x - CD4001 (IC1)

1x - 7812T (IC2)

1x - Green LED (LED1)

1x - Red LED (LED2)

2x - 2N3904 (Q1, Q3)

1x - 2N3906 (Q2)




1x - 12V coil Relay (RLY1)                                         Jameco P/N: 144186

4x - 2 Terminal connector (X1, X2, X3, X4)           Jameco P/N: 2094485*

1x - Printed Circuit Board                                        Eagle files included in step 3

1x - 14pin IC Socket
1x - 120V/12V @ 250mA transformer  or AC-to-AC wall adapter, Jameco P/N:2076543

*This P/N was replaced to match PCB pin spacing. Old P/N was 2094506


Step 6: Assembly

Solder in passive components first, this includes resistors and electrolytic capacitors paying attention to polarity marks. Next, solder in power supply components such as diodes and voltage regulator paying special attention to polarity as well. Use a clip-on heat sink between solder joint and the body of semiconductor as shown in pictures.

Install the 14-pin IC socket and solder it in place. Use just enough solder for each pin to keep adjacent pins from shorting together with excess solder. Note the position of the notch on one side.

Using an external +15V DC Power Supply (or two +9V batteries in series) and a couple of alligator clips, connect the (+) output of this power supply to the anode of D1 and the GND output of the power supply to the cathode of D4. Measure voltage between pins 14 (Vdd) and 7 (gnd) of the IC socket which should be +12V +/- 2%.


If this voltage test proves successful, proceed to next step.

Step 7: Finish Assembly

Install 2N3904 NPN transistors into Q1 and Q3 positions making sure all terminals go into their corresponding holes. Attach the clip-on heat sink before soldering each lead with the right amount of solder and wait at least 20 to 30 seconds before moving to next lead of same device. Do the same with 2N3906 PNP transistor on Q2 position. Install the green LED into the LED1 position. The shorter lead is the cathode and should go where the cathode lead is marked on the PCB. If LEDs are reversed they won't turn on. Attach clip-on heat sink to the lead you will solder first, wait 20 to 30 seconds before soldering the anode. Do the same with the red LED into the LED2 position.

The remaining terminal connectors come with two terminals each. Install one connector each into X1 and X4 positions and solder in place with the terminals facing to the edge of the PCB. The terminal connectors used come with a sliding lip on one side and a groove on the other. Take the remaining two connectors and put them together by sliding one connector's lip into the other connector's groove so they stay attached and insert them into X2 and X3 positions and solder in place with terminals also facing to the edge of the PCB.


Install the relay into RLY1 position and solder it in place. This completes the assembly of the controller board. In order to have the controller ready for testing, insert CD4001 into IC socket.


Step 8: Final Testing

Place your assembled controller board on an insulated surface such as a file folder or notebook on your workbench to avoid shorting the solder joints with any lingering conductive material still sitting on your work surface. Get a couple of one foot 24AWG segments of wire and strip the ends. Insert one wire's end into the terminal marked as "Ground", then insert the another wire into the terminal marked as "Pump level protection" leaving the other ends loose without touching one another.


This is a test with the same DC power supply used in step 6. Connect it the same way to power up the circuit. At this point, the CD4001 should already be inserted into its socket. Once power is applied to the board and assuming everything was properly assembled, the red LED should come on. If you put together the two stripped ends of the wires previously attached, the red LED should go out and the green LED should come on and one click should be heard coming from the relay. Separating the wires' ends should turn off the green LED and the red LED on while hearing another click from the relay as it de-energizes. This proves the circuit is working.


Get yourself a small shallow container and fill it up with water. With the circuit still energized, the red LED on and the two wires not touching to each other, dip both stripped ends into the container with water. The red LED should turn off and the green LED should turn on with one click heard from the relay. Remove the wires from the water and the green LED should go out, the red LED should turn on with a click heard from the relay. If this goes as outlined, then it is working properly.


AC transformer test:


Now it's time to test that the controller will work with 12VAC coming from the 120V/12V 250mA transformer. Connect the transformer's 12VAC leads into the connector marked as 12VAC IN. Plug the  transformer's primary through an extension cord into a wall outlet and the board should perform the same as with the DC power supply. If this is the case, then it's time for next test.


Water Pump test simulation:


Get another pair of wires of about the same length as the wires already connected to the controller board, strip their ends and insert one in the "Low level" terminal and the other in the "High level" terminal. With the pump protection and ground wires already dipped into the water container, the green LED should be on. Dip the "low level" wire end into same water and the green LED should still be on, then dip the "High level" wire also into same water container and the green LED should go out with a click heard from the relay. This simulates that the pump filled up the water tank. To simulating water consumption as water level goes down, remove the "High level" wire from the water container and nothing should happen. Then, remove the "low level" wire from the water container and the green LED should turn on and the relay should energize the water pump and the cycle will repeat.

If tests were successful, the controller can now be used in the real world. Before doing it, get yourself a suitable enclosure so no hot voltages are exposed. The electrodes in the water tank can be placed vertically from the top of the tank down into the water. To avoid corrosion, it is recommended to use stainless steel electrodes for longer life. If electrodes go through the wall of the tank, seal properly to avoid leaks.





Hi Lado115,<br><br>Based on your comments, would waves affect the high level sensor, or the low level sensor?<br><br>I believe maybe the high level sensor could stop the pump sooner because of water filling up the tank. How high would the waves be? Would the differential of actual water level be too high with respect to sensor? I don't think it would be. However, if that's your request I believe I can come up with something.<br><br>If it's the low level sensor the one that could be affected which would stop the pump sooner, please let me know.<br><br>Rlarios<br>
<p>Dear <a href="https://www.instructables.com/member/rlarios" rel="nofollow">rlarios</a> greeting of the day, Thank you for the the such a awesome circuit design . Dear sir i want to make some delay around 3 second on base tank sensing probe of this circuit what can i do for it kindly help me waiting for your replie</p>
Hi Lado115,<br><br>Thanks for your comments.<br><br>Where exactly would you like to introduce the delay and why?<br><br>Regards<br><br>Rlarios<br>
<p>Hello sir,thank you for your quick regards.The reason that i'm asking you for the delay in base-tank sensors is that i took the waves formed in base tank for whatever the cause,into consideration.And i think such waves could affect the relay switch by switching it on and irregularly.So i hope you could make some arrangements on this issue.Looking forward to hearing from you ASAP!</p><p>Sincerely yours</p><p>James decoy Lado </p>
<p>Dear <a href="https://www.instructables.com/member/rlarios" rel="nofollow">rlarios</a> greeting of the day, Thank you for the the such a awesome circuit design . Dear sir i want to make some delay around 3 second on base tank sensing probe of this circuit what can i do for it kindly help me waiting for your replie</p>
<p>hi sir can you share with me the eagle files? so that i will not have to make the whole schematic and just modify the existing one that you have ? </p><p>thank you <br></p>
<p>Hi:</p><p>Great project. We have some large (six feet high) poly tanks at the cottage we use to store water. Will the pobes work on tanks this large? What is the maximum distance between the probes?</p><p>Thanks</p><p>Jeff</p>
Hi there Bundolo,<br><br>Two years ago, one reader had a kit installed to control a 1,600 gal tank located under a deck (6.5' height). The tank was used for irrigation somewhere in Oregon.<br><br>I haven't tested what the maximum distance between high level electrode and ground could be. I guess that's something I'll test during this coming weekend.<br><br>Thanks for your comments Bundolo.<br><br>Rlarios<br>
Thanks Rlarios<br>we'll be trying out several approaches for monitoring the tanks this summer. We'll try your method, and also monitoring the tanks with a sensitive pressure sensor, and an ultrasonic method. Ultmately I want to be able to monitor them remotely, they're about 250m away from the cabin, so exploring methods of doing that as well. Should be a fun project. when I get it all put together I'll put it on Instrucables. Any suggestions welcome.<br>Jeff
hi, thx for the great toturial. I've redesigned the circuit and make it more compact. just removed the voltage regulation part and re order other parts. it's working now in my aquarium with titanium sensors. thx again.
Please sir send circuit diagram <br>prajapatianand7878@gmail.com
Anand7878,<br><br>Check step 3 of this instructable. Circuit schematic diagram is shown right there.<br><br>Rlarios<br>
Dear Anand7878,<br><br>Circuit diagram is shown in the instructable.<br><br>Or, do you mean something else? <br><br><br>Regards<br><br>rlarios
Great work HamedI2!<br><br>I will really appreciate if you could share a link about those titanium sensors.<br><br>Thanks, sir.
<p>hi i was wondering can this circuit be used in reverse? i need to turn on the pump when tank is full and stop the pump when a certain threshold is reached </p>
Hi there Tycss,<br><br>Yes, it can work in reverse. If you are in a hurry, check the instructions I gave to &quot;Murray&quot; about three years ago on how to modify the circuit to do what you just asked.<br><br>I said back then I would write about these simple changes in the instructable, and I never did. Shame on me. I hope I don't forget this time.<br><br>Cheers!
Please sir i want to make it please send me circuit diagram on my whatsapp or email<br>prajapatianand7878@gmail.com<br>Whatsapp:-+919737020883
<p>Hi rlarios, i want to say thank you for sharing this wander full instructable and I have a question, hope you can answer.</p><p>Can this circuit work in 5v? I have tons of 5v phone chargers, would be perfect for me :)</p>
Hi Mark 62726,<br><br>Thank you for your comments.<br><br>You can have the CD4001 operate off 5V. You would need a 5V coil relay with contacts rated at least at 1A at 120Vac, and instead of the rectifier diodes and 7812 voltage regulator, you could use your 5V phone charger.<br><br>rlarios<br>
<p>I want to make a printed PCB. So what can I do. I checked your cadsoft eagle file but it is doesn't seem to work on my cadsoft eagle so what can I do. Pls send me PCB design in PDF format so I can print it and itche it on PCB.</p>
<p>Hey, I made the water level controller , it worked alright when i tested it in buckets, but after installing it in underground and overhead tanks, it dosent seem to work , it simply keeps the pump switched on although all the levels are submerged.</p><p>what possibly could be the problems ?</p><p>Please help me with it . </p><p>I can provide images if you need them.</p>
Hi there DarshP5,<br><br>Please provide pictures showing all electrodes in overhead tank which is the one that controls pump operation. <br><br>rlarios<br><br>
<p>First I tried using a aluminium strip , but the circuit dint work , so i used a metal Screw as i had tested with metal screws in the bucket, i have posted the pictures of them all , the black and blue wires are the ground , green is the lower level and the red one is the upper level , and the blue one is the pump protect. (dont worry the pump protect and the ground wires are submerged in the underground tank.) and the other wires are as shown in the picture. Any Help Would Be Appreciated . :) thanks<br></p>
<p>DarshP5,</p><p>Wires wrapped around screws the way it's shown in pictures won't work properly. Crimp round terminals to wires ends and fasten terminals to either stainless steel or galvanized bolts using nuts and washers for a secured connection so they can be used as electrodes. </p><p>I believe you can find these bolts, nuts and washers at home depot or your local hardware store.</p><p>Let me know how this works. If you're still stuck with it at least we know electrodes won't be a problem. </p><p>rlarios</p>
<p>hey , sorry for the late reply.</p><p>i found out the problem , it was a small cut in the ground trace of the PCB , i fixed it, but now the circuit is acting weird , as it turns on the pump as soon as the water goes below the upper level. and then, the pump protect seems not to work and infact the circuit only works only when they are out of water. Its confusing ! please help :)</p>
DarshP5,<br><br>Show me a picture of solder side of your PCB.<br><br>rlarios<br>
<p>Sure, here it is </p>
First clean flux residue with a cotton swab soaked in alcohol. Make sure board is clean on component side as well.<br><br>Let me know if it still doesn't work so we continue debugging your control board.<br><br>rlarios
<p>Is this circuit is operate on AC current?</p>
<p>it depends on what you mean by that. Circuit operates on dc and I've seen some varying low voltage can be used and then rectified in order to be detected. </p><p>There are other circuits out there that operate off ac power using relays, in case you're interested look them up on YouTube. </p><p>rlarios</p>
<p>What to do to circuit to operate it on DC....</p>
<p>See comments below. </p>
<p>please can you send me the grafcet explain the operation of this project ???</p>
<p>please can you send me the grafcet explain the operation of this project ???</p>
<p>I put the cd 4001 in with pin 1 towards r1. Is that correct?</p><p>Better pictures would be nice for those of us who are color blind and too old to read tiny things.</p><p>Big question is can I substitute float switches for the top and bottom sensors to ground?</p><p>I could guess the 12 v dc needs to be on until the water lowers and breaks the circuit for the bottom sensor, and rises and finally breaks the circuit for the top one.</p><p>or vice a versa - My floats can go either way.</p><p>Going to use this to run a vegetable hydroponic garden on the balcony of my appt. About half of the time their roots will be submerged. </p><p>Have heard that plants are highly reactive (grow faster) to voltages - would like to run two test - one with the roots being grounded and the top of the plant with a weak dc positive charge, and another with the inverse. (will be an interesting test)</p><p>can I do that with this circuit? At least one of them?</p>
<p>Dear MikeL50,</p><p>Please review attached image. This DIP (Dual In-line Package) has an index mark on one end. Hold the IC so this mark is at your left, then the first pin below this mark is pin 1. Hand sketched drawing will show the pinout of this IC seen from the top.</p><p>Float switches (N.C.: Normally Closed) can be wired as shown in same picture as well. By the way, the attached picture was changed as previous one was not drawn correctly. </p><p>Hope this helps, let me know if you need anything else.</p><p>Regards</p><p>rlarios</p>
<p>MikeL50,</p><p>By the way, I forgot to confirm that CD4001 pin 1 goes to one end of R1 just as you said. The other end of R1 goes to +12V.</p><p>rlarios</p>
<p>Saq,</p><p>Replied though email and not sure if it will show up here in the forum or not. Try clicking the download pdf link, if not, go to the Jameco kit link below. Theory and schematic are in their docs I believe. Good stuff there. </p><p>Kid</p>
<p>can u mail me circuit diagram of this project.</p><p>shaikhsaqlain10@gmail.com</p>
<p>I built a radon mitigation system for my well water. This controller worked great!</p>
<p>hi, its a cool project, is there any way that i could get the pcb design?</p>
<p>Nice one! I have built a similar one on a bread board and tested by keeping it running for about an hour. Ionization leads to deposits on the leads/terminals inserted in water. Won't this affect performance over time and hence, required cleaning of such inserted leads periodically? If yes, is there any way to avoid this?</p>
Hi rlarious I'm back ;)<br>I was just thinking can we replace the transformer from that circuit<br>i.e, can we directly use the 12v dc adapter supply for the circuit<br><br>Can u plz tell me which components should be removed for that or how will the circuit be look like after doing that<br><br>I think those 4 diodes, 7812 voltage regulator should be removed but what about the capacitor<br>Plz help me out soon
<p>Remove capacitor as well. If wires from DC supply are longer than 3 inches, install a 0.1uF cap.</p><p>One more thing, make sure your DC PS is isolated from the mains by means of a transformer.</p><p>Good luck.</p>
Could you plz upload an image of the new schematic for the dc adapter, as I'm having some trouble with it right now<br>Thanks once again.
<p>The DC adapter you intend to use should have an isolation transformer inside. This means, there must not be any electrical connection between mains and the adapter's output such as is the case when these adapter's rely on auto transformers. The +12V DC and ground wires from your adapter would go to the +12V rail and ground line of the circuit, respectively. Forget about the 0.1uF capacitor. This is simple, just two wires from your adapter to the control.</p><p>rlarios</p>
One more thing shall i remove all the capacitors , 4 diodes, and 7812 regulator
<p>Remove D1, D2, D3, D4, C1, C2, and 7812 voltage regulator. Leave C3 installed.</p>
this design for water level control is the best i have seen in terms of simplicity of design and dedication to control limits. How can i get about 25 pcs of the pcb used in the design?, as other components is already available here.
Stevobaba411,<br><br>Unfortunately, the only source for ready built kits is jameco:<br><br>http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2169109_-1<br><br>Thanks for your comments.<br><br>rlarios<br>

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