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I have very little knowledge of PCBs and electronics, so bear with me.

I have a requirement where I have to read the temperature of an object. The thermocouple part has been figured out and currently we have a very simple setup with an Arduino Uno using a MAX6675 (thermocouple ADC) and displaying the temperature on a LCD.

Next step of the project is to to eliminate the LCD, try to design a custom PCB which contains the microcontroller, ADC (it doesn't have to be MAX6675) and accessories to send the data to a host PC or save the data in an SD card, whichever is feasible and the program for all of this.

The reason for a custom PCB is because the PCB has to be around 18mm in diameter as it will be mounted on the object whose temperature has to be measured. It needs only one input and output as we will be measuring just one temperature point with one PCB.

Is this all possible in a custom PCB and can it be made that small?

I am trying to educate myself and look for possible problems before I talk to PCB manufacturers.

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    \$\begingroup\$ Sounds like you are embarking on an interesting project. Alas, your question is too open-ended and broad to fit here. Stack Exchange sites are reserved for narrow, specific questions, not general advice. It does seem like you need to be talking to an experienced PCB design, not a board manufacturer. Also if you are going to mount the electronics on the thing being measured, a relative measurement device like a thermocouple won't be much help. Rather you probably want just the RTD or thermistor that a thermocouple would be referenced to if it were measuring something remote. \$\endgroup\$
    – Chris Stratton
    Commented Jan 22, 2018 at 8:37
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    \$\begingroup\$ Do you mean 18cm? Or did you mean to say mm? If it is 18cm in diameter, you will most likely find you have a HUGE amount of spare space on your PCB, I would consider that quite large! \$\endgroup\$
    – MCG
    Commented Jan 22, 2018 at 8:50
  • \$\begingroup\$ it is 18mm and I fixed the post. THank you for correcting me! \$\endgroup\$
    – Vish_evo
    Commented Jan 22, 2018 at 9:05
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    \$\begingroup\$ Look at Analog Devices for thermocouple to voltage, and at Maxim for thermocouple to digital ICs (though maybe they both do the other type as well now) \$\endgroup\$
    – Neil_UK
    Commented Jan 22, 2018 at 9:14
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    \$\begingroup\$ I think the 18mm diameter PCB is very feasible - that's about the size of the average smartwatch PCB. However for best results you'll want to subcontract the design, since it's quite hard for beginners to work at that size. If you're still learning PCB design do a version #1 without the size constraint and then see how to shrink it using small SMT or BGA parts. \$\endgroup\$
    – pjc50
    Commented Jan 22, 2018 at 11:01

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It is absolutely possible to fit that into a PCB that size, you can give it a quick try using an online PCB design service such as EasyEDA. What do you mean by 'a custom microcontroller'? If you are willing to do some SMD work, you could get an ATmega328P on the board, and a few passive components to make to work. Then you can either save data to an onboard SD card, or to a connected computer.

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  • \$\begingroup\$ I mentioned the work custom because we need to measure only one temperature point and send it to a PC or save it in an SD card and the PCB can be designed with the size constraint. Unlike the off the shelf boards like UNO R3. It has lots of I/Os and that many would take up more space in the board, if I understand the basics of PCB design correctly. \$\endgroup\$
    – Vish_evo
    Commented Jan 22, 2018 at 9:10
  • \$\begingroup\$ @Vish_evo I don't mean an off the shelf Arduino board, I mean the microcontroller found on the Arduino nano board, it's tiny, and it will fit on your PCB with room to spare. \$\endgroup\$
    – skillz21
    Commented Jan 22, 2018 at 9:16
  • \$\begingroup\$ Yes I understood that @skills21. I was just skeptical about this project due the size constraint of 18mm. I will do some research on the uC and go from there. Thanks a lot. \$\endgroup\$
    – Vish_evo
    Commented Jan 22, 2018 at 9:22
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    \$\begingroup\$ Oh sorry, I didn't see that you wanted 18mm.... in that case, if you really tried, you could probably squeeze the MAX chip and the ATmega328P on the PCB (of course, if it's double-sided), and the passive components, it would be really difficult to solder all of that but I think it would be possible... barely... Oh, you could go with something like an SMD ATtiny 85... that would give you a lot more space. \$\endgroup\$
    – skillz21
    Commented Jan 22, 2018 at 9:22
  • \$\begingroup\$ I read about Atiny 85 and the size specifications would be really really helpful for this project. \$\endgroup\$
    – Vish_evo
    Commented Jan 22, 2018 at 10:05

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