Looks like I’m not finished with my cooling project just yet. I’m going to change the board to handle two independent fans, and get the whole thing on a single board. The problem is that I really need to exhaust the hot air out from the back of the TV unit, so that cool air is dragged in through the front. I think I’ll need at least two 120mm fans to get enough air through.

I’ll use what I’ve learnt so far, and add a few more useful bits and pieces. First thing is to display the temp on startup for 3 seconds. Easy.

During the reboxing, I connected the power to test again, and got that puff of smoke from the Nano that augers bad news all around.

Now I just get the power light and nothing else, so I think that Nano has had it! I’m hoping it was the rubber band pushing a wire on the board into another one causing a short, as I had done no work on the boards themselves. I’ll only know when I program a new Nano and put it in the board, I suppose…

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To connect to the Bubble Display module, I mounted it on a piece of Veroboard, with the rails cut between the 2×6 pins. I left one row of extra holes on each side, and mounted some 90 degree header strip there, exposing the 12 pins at right angles to the display. I then took two length of 6 strand ribbon cable, put 6 way Molex connectors on for plugging into the display. But on the other end of the ribbon, I put 12 individual connectors on, this way, it was easy to match the bubble pin number with the correct shift register and pin at the board end. I do need to find some nice soft flexible cable though, all the stuff I seem to have is really stiff, and doesnt like being bent at certain angles!

I love it when things work first time. This wasn’t one of those occasions though! I had a problem where all of the output pins of the 2nd shift register were always high, meaning no digits on the display. It took some work with the voltage tester, but it was tracked down to a minute piece of stray solder, bridging two strips on the veroboard.

So the project is complete, barring the enclosure (currently the two boards are being held together by an elastic band with a piece of hard plastic in between!). So when I find a suitable sized enclosure, I’ll transfer it into there, but in the meantime, I’ll put up the board layout for the extra board, and the full code, once I add some comments.

There are just 2 points of connection between the original board and the new bubble display board. A twin connector to the ground and 5V on the bottom right, and a triple for the data, clock and latch. Fortunately there were three unused outputs from the Nano with unused rails. That’s the 2nd red box at the top.

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Here is the first step for part two of my cooling project. It uses just 3 outputs to drive a pair of shift registers, and ultimately a 4-digit bubble display!

Currently the display toggles between displaying 24.5C and 1496 (the RPM)… Why? Because those are the two hard coded values I’ve picked in my function calls!

Given its only 3 pins, my plan is to put it all on a different bit of Veroboard, and connect it to the original board with a plug! Exciting stuff 🙂

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Well, rather than struggle with a tool not designed for the job, I threw away any thoughts of doing the stripboard in MS Word. Instead I downloaded the demo of a bit of prototyping software called LochMaster 4.0. It natively does stripboard, and you can even flip the board to see the solder points and cut strips underneath! I’ve now purchased the software, as I think it’s going to be pretty handy.

Anyway, this is the top of the board, the Vin of the Nano is bottom right. The power connection to the red and black rails on the right is 12V. The 5V green rail is taken FROM the Nano, you don’t supply it.

Additional parts :

  • C1 – 0.1 uF cap to make the 3.3V reference voltage smooth.
  • D1 – Small diode to prevent back EMF from the fan. A 4001.
  • D2 – Small 5V LED (this and the resistor are actually entirely unnecessary, as the on-board LED would probably be enough)
  • T1 – The transistor at the top is for switching the fan on and off. I think its a BC337

Regarding the pin strip headers, the top (4-way) is for the PWM fan. The S pin is the RPM pin, and the P pin is the PWM signal pin to the fan.

The bottom 3-way header is for the TMP36 thermistor. Since I wanted to have this at the end of a cable, so I could position it where I wanted, I made it a header.

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This is the back of the board, showing the places where the strips need to be cut.

Code is to follow, when I’ve commented it and tidied it up. I’ll mark the Nano pins on my next project. You should be able to work it out from the circuit and the code though.