Arduino PID Temperature controller

Using Arduino Project Guidance
#1

Hi everyone, I just want to say that I'm very new to all this, and only recently found out about Arduino. It's all very exciting and exactly the kind of project I want to start.

So on to my project...I want to create a more refined version of a standard PID temperature controller similar to the only design I can find anywhere. (Check out: PID Controllers : Auber Instruments, Inc., Temperature control solutions for home and industry)

Those are made in the US but there are ton from China. Anyways, they all look the same and aren't the most user friendly. What I would like to do is use a rotary encoder and Graphic LCD to create a simple user interface where you can select a temperature via the encoder and set it by clicking the encoder. The LCD would show the current temperature as well as the SET temperature. The temperature would be picked up by a K type thermocouple and I would want the Arduino to control a nichrome heating element that uses 120V and 3amps.

I don't want to use a separate power supply to the arduino than to the heater. That's the part I'm most stuck on. Mos of the choosing stuff I'm thinking I can figure out. I've gotten separate components to work on the Arduino so I think I will be okay on that. But I haven't quite figured out all the parts I need and exactly how to wire everything.

What I have now:
Arduino Uno
Max 31855k Thermocouple amplifier
Rotary encoder
Graphic LCD
Four digit 7-Seg displayLCD (hoping it will be simpler to start with)
Thermocouple K
10a Solid State relay

I really hope I can get some answers from those more experienced or any one with a similar project. Also sorry if my post doesn't make sense in parts, I typed this all from my phone since my laptop is currently inoperable lol.

#2

As with any project, the best way to start is to break the project up into small projects that will each have an end result.

as I see one way of doing your project,
start with the temperature. get the UNO to read the temp and convert it to a value you want.

once you have an input, add the output. the SSR is not hard to use and you can interface the reading and output.

next might be the display. you have lots to display, raw reading, engineering units (deg F or C) output high or low....... a graph of temperature over time....

add the encoder. one suggestion is to only read it as it is moving and do not buffer the inputs. that way a 'spin of the dial' does not have the value running past where it should be.

at that point, you would have the entire project operational on your bench.

once you have your project working with store bought boards like the UNO, you can start to look at a custom board and enclosure.

to look at the power supply before you got any of the rest working is the cart before the horse. only once you have it working will you really know parts selection to determine the actual power consumption and then power demand on the supply.

I would offer that you might be able to shoe-horn a wall wart into the enclosure to create a nice package.

I would also offer that for a better control, you will want a more sensitive analog input than 10bit. someone told me years ago that you should be measuring at least 10 times more accurate than you want to control. so if your thermocouple reads 0-1,000 degress and your I/O is 10 bit, you have one degree per step. with an error of +/- one step. so from the start, your measuring has a window of 2 degrees. if you try to measure within 2 degrees, your system will be unstable. if you could read 10 steps per degree, your sensitivity would be high enough to control within 2 degrees.

the final power supply problem will be something that will reveal itself once you have the rest of the system working. if you try to choose one now, you may find it is half the size it needs to be or twice as large. enclosure selection might be different and so on.

#3

Thank you so much for your reply, Dave. I agree with starting with individual components and working on smaller projects before bringing them together. I am already starting to do this be getting smaller components to work such as an led and the rotary encoder (to change brightness of LED for now). I will now attempt to get the display to work and display the temperature the thermocouple is reading.

The power supply problem is something I had only recently thought about. I've seen many similar projects with heating elements and a thermocouple or temp sensor. But they seem to use two supplys, a USB for the arduino and whatever is needed for the heating element, or the issue does not get addressed.

I did think about taking apart a wall wort, but I was hoping I could buy a specific component that could do this, I just don't know what it is called.

#4