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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 ;-)

3 pcs, 150x150 mm liquid crystal sheet (29-33°C) (see here).
17 pcs, copper plates, 1mm thick (dimensions see below)
401 x 220 x 2 mm aluminium plate (grey/black anodized)
401 x 220 x 2 mm acrylic plate (white)
18 pcs, TES1-12704 peltier element
9 pcs, TB6612FNG dual motor driver
6 pcs, Arduino Nano
2 pcs, 40x40x10 mm cooling fan
18 pcs, 25x25x10 mm heat sink
12 V, 6 A power supply
DHT22 (AM2302) temperature and humidity sensor
6 pcs, 40 mm long PCB standoffs
In addition, I used this thermally conductive epoxy which was rather cheap and has a long pot life. A drill and dremel tool was used to make the necessary holes in the aluminium and acrylic plates. Holder for the arduinos and motor driver PCBs were 3D printed and attached with hot glue. Also, I used lots and lots of dupont wires to make all the connections. Furthermore, this PCB with screw terminals came in very handy to distribute the 12 V power supply.

Attention: Apparently, many of the TB6612FNG boards do have the wrong capacitors installed. Although all sellers specify the board for motor voltages up to 15 V, the capacitors are often only rated for 10 V. After I blew the capacitors on my first two boards, I desoldered all of them and replaced them with proper ones.”

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