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Thermochromic Temperature & Humidity Display

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I have been working on this project for quite some time. The original idea came to me after building a TEC controller demonstrator at work for a trade fair. To show the TECs heating and cooling capabilities we were using thermochromic paint that changes from black to transparent.

In this project I have taken the idea further and build a two digit 7-segment display using copper plates that are covered with thermochromic sheets based on liquid crystals. Behind every copper plate sits a TEC element that controls the temperature and thereby changes the color of the liquid crystal sheet. The numbers will show the temperature and humidity from a DHT22 sensor.

You may appreciate the irony of having a device that displays the ambient temperature by changing it's own temperature ;-)

Step 1: Making the Copper Plates

For the copper plates I used an online laser cutting service (see here) where I could upload the attached dxf files. However, since the shapes are not very complicated, laser cutting is not a must and there are probably cheaper manufacturing techniques (e.g. punching, sawing). In total, 14 of the segments, two circles and one dash are needed for the display. The thickness of the copper plates was 1 mm but could probably be decreased to 0.7 or 0.5 mm which would need less heating/cooling power. I used copper because the heat capacity and thermal conductivity is superior to aluminium but the latter should also work reasonably well.

ethansocks811 days ago
Wow. Just wow. This is super cool. Sure to get at least first prize.
calcot20 days ago
That is really, really cool!
Makerneer20 days ago
Cool project, thanks for sharing!
Really nice project. I want to replicate it. What was the approximate cost for this?
mosivers (author)  ibrahimmusba25 days ago
Thank you. I have to calculate the costs and will add them later to the instructable, it should be around 200 EUR.
DmitriyU226 days ago
Great display idea, but why you use expensive peltiers instead of simple heaters, as example you may make it on PCB? 2 UNOs also overkill, there are ways to extend one.
mosivers (author)  DmitriyU225 days ago
That is a good point, I also thought about just using heaters. However, the peltiers were not that expensive (~ 2 EUR/pc) and I wanted some quick way to change the color of the segments back to black. Also you could operate the display at ambient temperatures above 29°C where the color change starts.
mpcleverdon27 days ago
Great project , to keep it cool I though that a peltier would heat/cool depending on the +/- configuration so no fans would be necessary, surely it's possible to invert the voltage?
mosivers (author)  mpcleverdon26 days ago
Thank you. You are correct, the peltiers will heat or cool the copper segments depending on the polarity of the applied voltage. The fans are just used to prevent the backplate from heating up too much over time.
Vibrations27 days ago
Does anyone know how my backyard neighbors are tasing me? (sending an electric shock to me) and also putting vibration sensations on me. My husband cannot feel this. Can they do this through my iPad camera or iPhone camera. Please help me figure this out. My email is sassyjbh@bellsouth.net. I have filed a report with the sheriffs office. They say I need proof this is happening so I thought if I could figure out how they are doing this without direct or physical contact they would believe me. The guy behind me is a technical engineer with the Nissan company. They can also shock me while I am in my car, so maybe they are using radio frequencies, gps, WiFi?.?? Any help would be greatly appreciated! Judy Holliman

Gourdhead27 days ago
I'm wondering if this would work outside. It seems to me that the temperature around the display would have to be maintained constant in order to prevent it's displaying the wrong temperature.
mosivers (author)  Gourdhead27 days ago
If it gets too hot or cold outside the heating/cooling power of the peltiers will probably not suffice to completely change the color of the foil. One would also have to add a weather proof housing for the electronics.
This gave me an amazing idea! I´ll post photos when I make it. Very nice.
mosivers (author)  Helder Cabral27 days ago
I am excited to see, keep me posted.
BerenV27 days ago
Cool technology to use in a display! Have you heard of I2C PWM expanders such as the PCA9685? If you used those plus an I/O expander, you could run it all off only 1 Arduino, thus lowering the cost and complexity. Actually, come to think of it, the SX1509 is an awesome I/O expander that can also do more autonomous PWM stuff as well.
mosivers (author)  BerenV27 days ago
I have used the PCA9685 in a previous project. I will check out the SX1509 as well. Reducing the amount of components and wiring would be nice
curiosity3627 days ago
"In this project I have taken the idea further". There's no limit to the creative mind. Beautiful. Thanks for posting.
randofo27 days ago
This is very clever! Nice job :)
Wo1fMane28 days ago
That's awesome! It's mesmerizing, ironic and perfect.
Leomiracle29 days ago
Such a cool and hot project! Thumbs up!
Hersoft29 days ago
Wow, yes I know and used tecs but never thought of doing something like this.
Great job!
Loved the concept. Refresh rate is a bit low but works for the use case ;P
Honus1 month ago
That is really, really cool!
I love it! What a stunning display :D