Make a Simple Hygrometer for 0$ !! (great for Your Childrens!)




About: Crazy and creative Industrial design student at Kielce Technology University.

Since I posted my last instructable about simple science (you can check it out here) it get 41,501 views, so I decided to post another one. And today you will learn how to make a simple hygrometer, Another project that is fun to make with kids, and it is educational as well.

If you're curious about how it works, check last step ;)

Step 1: You Will Need...

Here are the things you will need to make the hygrometer:

  1. Scissors
  2. Sharpie, or a pen
  3. piece of paper (preferably thicker than regular printing paper, i used 180g/m^3)
  4. piece of cardboard/thin plywood/something that you can pin the pin into
  5. ONE hair, preferablu longer than mine - about 5-7 cm long

I Highly recommend to use horse hair. It reacts better and more noticeably than human hair.

But unfortunately my horse was drinking beer in the pub.... so I used my hair. ;)

Step 2: OK! Now We Can Start Learning.

Try to draw an arrow on paper, it don't have to be big, look at mine arrow, it can be similar. Then you have to cut it out using scissors.

Remember! always be careful using scissors and don't let kids to play with them when you are not around.

Now the most important part, You have to make hole in arrow and make a pivot point. The hole need to be a little bigger than pin so the arrow can move freely. You can check it by twisting the pin - when arrow always point down no matter which way you turn the pin.

When you finish arrow pin it to the cardboard/plywood and check if the arrow spins freely.

Step 3: Tape the Hair to the Arrow and Cardboard.

Cut small piece of tape and stick it to the hair and then to the arrow. Pin the arrow to the cardboard and tape the other end of hair to it.

Basically you finished ;) But I have added some graphics to it, so it look quite better.

Step 4: But... How It Works?

Here is how it works:

Hair have special hidden ability to shrink when dry and expand when wet. Using this fact, when there are more moist in air the hair will be longer and the arrow will point more downwards. When the air is dry, the hair will shrink and move arrow upwards.

The longer the hair is the more visible is arrow movement. You can use horse hair to make it more visible, since horse hair reacts stronger on humidity changes and moves arrow more visibly.

It's a project great to make with children and show them some science ;) but you can use it to check the changes in air humidity in your room ;)



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    15 Discussions


    2 years ago

    I am doing a science project at school and this will help a lot so thanks!


    4 years ago

    I can see where you are going with this. However, I think the reading on your meter will be so small that it will be hard to see any difference at all :-/

    3 replies

    Reply 3 years ago on Introduction

    Attaching the hair closer to the pivot point (or alternatively extending the pointer beyond where it's already attached) would help with this. The further the pointer extends beyond the point of contact with the hair, the more noticeable small changes will be.


    Reply 4 years ago on Introduction

    We used to use longer hairs and wrapped them around a partly-straightened paper clip [or long thumbtack or map pin] pushed through a hole in thin wood or sturdy cardboard. Using a longer indicator needle [arrow] or arm of the paper clip allowed us to see smaller changes and allowed for rough calibration.


    Reply 4 years ago on Introduction

    Like I said, the longer is the hair, the more visible is change in lenght. Also, using the horse hair will give you better results than using human hair. The idea is probably older than me, so I am not surprised that there is a tutorial somewhere else ;) thank you for comment


    3 years ago on Introduction

    I used to make these when i was young. works really well, but i would make the arm longer with ofcourse the attaching point of the hair close to the center. That way you get better readings


    4 years ago on Introduction

    This brings back memories of doing this when I was a young
    boy, along with other basic science projects and demonstrations. Nice to
    see it's still being done. I remember experimenting with different color
    hair and hairs of different textures and thickness, but I no longer recall the
    results. Some parents trying this with their kids who think the only hair they
    have to use is their own, may actually have access to horse hair and not
    realize it. If their children play violin [or if they do], they may forget
    their bows are typically strung with horsehair, unless they switched to
    synthetic hair. Since broken hairs are common, the pieces can be used for
    your Instructable. I really appreciate that some of your projects are
    intended to be done with our children!


    4 years ago on Introduction

    You know, the problem with human hair is that it's normally oily. This keeps moisture out, which is normally good, but is a problem for a hygrometer.

    You should run the hair through alcohol or dishwashing liquid several times to get rid of the oil, and watch for oily fingerprints. This should give you a more responsive meter!

    (Idea from BBC's Rough Science)


    I wonder what is a good way to calibrate this. If you create your project when it is very humid, and you make your middle mark in humid weather. When the weather becomes dry you will think it is always dry.

    Ideally you would want to create your project when the air is neutral if you are going to start your arrow off in the middle.

    Or maybe you could create it in the steamy bathroom and start the arrow in the humid zone? Any thoughts?

    1 reply

    Reply 4 years ago

    Good question! I think that my answer will be "hey there is no need to calibrate! It's just to illustrate the nature of hairs". But calibration of this thing would be a big problem, you can read Wikipedia, and it says that It was very inaccurate way to measure humidity in air, also, steamy bathroom won't help I think because it take some time for hair to change it's lenght. Thank you for comment, good questions are the key to get more knowledge ;)


    4 years ago

    Hey - I am not a kid and I learned something new from this! When I WAS a kid my parents got me a series of science experiments, each in a little box. This reminds me of those - it was so much fun to discover something for the first time. This would be a great rainy afternoon project. Thanks!

    1 reply