This is a simple rain sensor circuit which can be built by a school grade student very easily and can be used for displaying its relatively useful feature, probably among his friends or in a science fair exhibition.
Using IC 555 as the Comparator
The circuit is basically rigged using IC 555 as a comparator and is typically configured to sense the low resistance through water across its relevant inputs.
Let’s try to understand how to build a simple rain sensor circuit using the IC 555:
Referring the figure, we see a rather simple design made around a single active component which is the IC 555.
Other than the IC, the circuit just includes a few cheap passive components like resistors and capacitors.
We are familiar the two important modes of operation of the IC 555, which are the astable and the monostable multivibrator mode, however the IC is laid down in a rather unusual fashion, quite like a comparator.
How it Works
As shown in the figure, sensing terminals are received across the positive and pin #2 of the IC via R1.
When water (due to rain fall) comes across the above inputs, a low resistance is developed here. The preset P1 is suitably adjusted such that any type of water across the sensing inputs triggers the IC appropriately.
The sudden low resistance at pin #2 of the IC acts like a pulse which exceeds the potential at pin #2 more than 1/3 of the supply voltage.
This activation instantly makes the output of the IC go low, ringing the connected buzzer. The buzzer circuit is comprehensively explained here, if you wanted to build one.
As long as the sensing input stays immersed under water, the output continues with the above situation.
However the moment, water is removed from the specified input terminals, the potential at pin #2 reverts to less than 1/3 of the supply voltage, making the output go high, back to its original position, switching off the buzzer.
The above operation effectively indicates the commencement of a rain fall when the sensor is appropriately placed for the detection.
The charge inside the capacitor C1 keeps the buzzer ringing for some period of time even after the water from the sensing inputs is completely removed.
Therefore the value of C1 must be appropriately chosen, or may be completely eliminated if the feature is not required.
Making the Sensor Unit.
The explained rain sensor circuit obviously needs to be placed indoors, therefore only the sensor terminals are required to be positioned outdoors through long connecting flexible wires.
The figure shows a simple way of making the sensor unit.
A small plastic of around 2 by 2 inches is used and a couple metal screws are fixed over the plate. The distance between the screw should be such that no residual water is able to stick or clog between them and water formation across it is detected only as long as the rain fall persists.
The wires from the screws should be carefully terminated to the relevant points on the circuit. The circuit must be hosed inside a suitable plastic enclosure along with the buzzer and the battery.
Parts List
R1 = 1M, R2 = 100K,
P1 = 1M preset, can be replaced with a 1M fixed resistor
IC = 555, C1 = 10uF/25V,
Simple Rain Sensor Circuit using a Single Transistor
If you think the above circuit a bit over complex, then perhaps you could implement the design using a single transistor and a resistor, as shown in the following image:
The working of the above circuit is rather simple. When water droplets or rain droplets fall on the sensor device, made using screw heads, the water bridges across the screw heads allowing small electrical current to pass across the metal, triggering the base of the transistor. As soon as this happens, the transistor begins conducting and amplifies the conduction across its collector/emitter terminals.
This results in the switching ON of the connected buzzer which now begins buzzing or beeping indicating the commencement of rain outside, and warning the user regarding the same.
Alternate Rain Sensor/Alarm Circuit Using the IC LM324
An alternative version of a rain alarm circuit can be seen below using a single IC LM324
Rooh says
Thanks Sir. Circuit works well on the breadboard.
Swag says
you are welcome Rooh, glad it worked for you!!
JOHNBELL says
Can I use this with 12V power circuit to ride in a vehicle, to drive the windshield wiper
Swagatam says
yes that's possible, just replace the buzzer with a relay and use the relay contacts with your wiper motor switch
Anonymous says
Hi,
I was studying your diagram for the first circuit using IC 555 and I noticed that pin 6 is right where pin 3 should be when I consult the diagram that came with my IC 555. In the above comments you mention that pin 3 is not labeled by mistake. Perhaps you have simply mislabeled pin 3 and not labeled pin 6. Please correct me if I am wrong.
Swagatam says
Hi, thanks for your interest….. however all connections in the above design are correct, pin3 is connected with the buzzer. The design has been tested number of times with perfect results.
Anonymous says
Good day,
I am a physics student building an automated door for a telescope and it needs to be able to detect rain and snow. Can this circuit be adapted to test for snow?
Swagatam says
Good day,
You can try measuring the resistance of snow one inch apart, if it's around 300k then this circuit would do the job for snow too.
Anonymous says
Thank you very much!
Anonymous says
I just want to ask if the materials thay are needed in this rain detector are expensive? What is the range of the price? Thanks
Swagatam says
All the components are extremely low cost.
uzair shaik says
awsome bro it worked
Swagatam says
congrats bro!
Anonymous says
can i follow ur step s in making mine
Austin Hamon says
I stumbled across this project while looking for a rain detector. I have a garage door on the roof a building that I open to allow it to cool. When it rains I need it to close and the garage door controller has a connector for a rain detector. I was going to hook the garage door controller up instead of the buzzer. My only question is, how would you calculate the capacitor size needed to keep it closed for x amount of time? I was hoping to keep the door closed for 15 minutes after it stopped raining. Thank you for posting this
Swagatam says
capacitor size will need to be figured out through trial and error.
the controller might need a (+) response for actuating, in that case you may have to interchange the positions of the sensor plate and P1.
Austin Hamon says
Awesome. Thank you for the help
Swagatam says
You are welcome!
Anonymous says
Hi swagatam thankyou for sharing your knowledge with electronic hobbyist. Can I use relay in place of buzzer to activate wiper of the car please reapply me
Swagatam says
yes, surely it can be done in that way.
sskopparthy says
do this circuit work?please tell me.
Swagatam says
yes it works
sskopparthy says
thank you sir.I tried it,it worked and it helped me save my mango pickle which was kept out to dry,it was nearly 4.5kilo grams!thank you very much sir
Swagatam says
very interesting:)
Tabish Hassan says
Hey do you apply the exact circuit???
sskopparthy says
Yes same circuit and it worked flawlessly…
Zul Fikri says
can you help me…. what type capacitor you used??? electrolytic or ceramic???
Swagatam says
In which circuit? in 555 it's electrolytic
Anonymous says
Hey, nice project. But just one question… On what leg in the 555 IC is the buzzer connected to?
Swagatam says
Thanks!, it's on pin#3, not shown by mistake….
Anonymous says
Sir,
I've got this project but they have used ic-lm324n, which is a four quad amplifier, can you elaborate the use of this ic. I've to submit this project for boards
Swagatam says
You will get it tomorrow, I'll let you know when it's published.
Swagatam says
The required circuit has been updated in the above article….
Amit Wasnik says
hey friend,
Its really a nice circuit but in case I need a digital circuit not an analog one. I mean, using '74' ICs. I have infact the circuit design for it (specifically 7400) but I need a rain sensor as a component. I am now trapped because it is not available in small scale market. So my query is that can I use such plastic made sensor, or else can you explain how resistors are selected on the drop of water on the screws? Please help.
Swagatam says
Hi,
Basically all rain sensor circuits depend on the detection of rain water resistance across the given two metallic points. This resistance is not a critical value, can be anywhere between 150K and 400K depending upon the water purity. The resistor value which needs to be selected in series with the sensor metal is also not critical, a minimum value may be selected say a 1K resistor, or anything close to it will do.
The sensor may be made as per ones own preference, the proximity of the two metals must be selected such that rain water can bridge the gap. The base can be any material which is a bad conductor of electricity.
keval thacker says
sir, i want to make automatic wiper system. so i want sensor that sense water on glass. plz help me.
Swagatam says
You will find it soon in this blog, so stay connected…thanks.
Anonymous says
can you please send it to me at v.arvind1998@gmail.com
Anonymous says
thanxx dude u helped me a lott 🙂
Anonymous says
can i use any other thing accept dis plastic for my sensor or tell me where can i find dis kind of sensor plz reply me soon
Anonymous says
if you don't mind kindly send it to my email smashkid21@yahoo.com
Anonymous says
thank you very much.I am a beginner and i really want to make this project. But since i am not too familiar with the components and its connections, will you please help me understand the circuit by identifying its connections.. i mean where to connect the positive and negative terminals and one thing, I was bit confused where is the output or the pin 3 of the 555 timer is connected. I am very much interested with this project. I really need your help. Im planning to make it for my project..
Felex says
ok, this one looks easier. thanks alot. where gonna buy those components and try it, and if there's any problem we it, we just gonna inform you, and about the sensor, can we use a plastic plate? is it no foil at all? i just confuse. thank you soo much!
Felex says
sounds clear to me. thanks alot. 1 of this days maybe i already done it. thanks for your help.
Anonymous says
hi..we are interested on this project can you help us to elaborate well on how to make the sensor terminals? or can you show us some picture? please. thanks.
Anonymous says
Hi, my name is Rubby and am doing something on automobile circuit to detect rain and close please can you help me.This is my email address rubbyaworka1@yahoo.com. Thank you
Swagatam says
Please explain me the whole design requirement, I'll try to hep.