LCD Vacuum Sensor

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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Nicolas Krause
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Re: LCD Vacuum Sensor

Post by Nicolas Krause » Wed Apr 28, 2021 10:50 pm

It's been awhile since I've updated this project, but I've completed my exams and have a bit of break before summer term starts. I received the updated PCB a month or so ago, and have in my spare time assembled it. I'm in the process of completing the program for the device. I just confirmed today that the connection from the LCD to the microcontroller works as I was able to write basic character values to the screen. I've completed a cable to connect to the vacuum thermocouple gauge itself. But the next few steps are as follows.
  • Confirm power to thermocouple
  • Obtain measurement from ADC
  • Write measurement to screen
  • Complete program and confirm it all works together.
signal-2021-04-28-164420.jpeg

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Nicolas Krause
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Re: LCD Vacuum Sensor

Post by Nicolas Krause » Sun May 09, 2021 11:29 pm

Just by way of a quick update, the program is mostly completed and written using fixed point numbers for calculations. The core conversion function is demonstrated in the code below. While testing the final elements of the program I identified an error on the circuit board that required a third revision. I've corrected the schematics and gerber files have been sent off to the boardhouse. When the replacement board arrives I can put it all together and hopefully be finally done!

Code: Select all

: CONVERT ( MEASUREMENT -- PRESSURE)
	\ a word to convert the value from the circuit into a pressure value.  
	\ firstly I take the very small value from the TC Gauge, and jam it into an amplification circuit.
	\ The range on the amplification circuit is 0 -> 71.2 * Vmax. Here Vmax is 14mV so max input is 
	\ This function currently assumes a 6343 or KJL 1518 type TC tube.
	\ It implements an exponential function of the form y = 7,000,000 * x^(-2.032) 
	\ Where x is in the input measurement and y is the output in mTorr

s>df \ convert measurement value to fixed point
\ raise x to power -2.032
log2 2,032 f* \ take the log base 2 of x, multiply by our power
pow2 \ take the power of 2 to get rid of the log base 2
1,0 2swap f/ \ gotta divide our value into 1
7000000,0 f* \ put our scaling value for x on the stack and multiply
mfloor \ convert to integer by taking the nearest whole number 

;

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Nicolas Krause
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Re: LCD Vacuum Sensor

Post by Nicolas Krause » Wed Aug 18, 2021 4:04 am

Again a quick update, I'm now on the 4th revision of the board and the amplification circuit is working as intended. I might have to tweak some values in code but I can now solder in the screen and hopefully confirm the complete program works as intended.

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Richard Hull
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Re: LCD Vacuum Sensor

Post by Richard Hull » Wed Aug 18, 2021 7:10 pm

You are well along your way to getting this project done. I intend to point out in the radiation forum which is about the only purely electronic forum we have that a firm grip on mathematics is a must for any person seeking to implement a microprocessor based implementation of any instrument or interpretive adjunct to older gear.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Nicolas Krause
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Re: LCD Vacuum Sensor

Post by Nicolas Krause » Sun Sep 12, 2021 9:27 pm

Happy to report everything is working as expected. The shot below shows a test voltage source attached to the whole board and gauge. I have a small cable to finish soldering now, but the tough bit is done! I may have to tweak some values in code, but happy to be at this point. I may soon test the device on my chamber with just the backing pump going.
IMG_1756.JPG

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Richard Hull
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Re: LCD Vacuum Sensor

Post by Richard Hull » Sun Sep 12, 2021 9:40 pm

No matter how good we get at coding. Unforeseen errors, idiot mistakes and the real world typically demand tweaking, especially when we think we have it done perfectly. Tweaking can turn out to be an on going process over time.

I am glad you are finally finishing your work here. Once functional, you have a skill set few ever attain. Turning an idea into a real world device, via study of principles, application of programming skills and practicing the art of electronic interfacing to the real world returning data sought in a readable, recordable form. Yes, and understanding the math needed to be performed on the electrical input and keeping track of the units within the math...This math is rarely difficult, but programming from real world electrical pickups and translating it to good output data, demands some math be performed within the processor.

After a long time away from programming in robotics, I was determined to tackle the Arduino environment when I retired in 2014. That goal has been achieved.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Nicolas Krause
Posts: 180
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Real name: Nicolas Krause
Location: Canada
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Re: LCD Vacuum Sensor

Post by Nicolas Krause » Tue Sep 14, 2021 2:04 am

For anyone who wishes to replicate this project, the current files for the PCB along with associated documentation are all included at the following link on my GitHub. The code may require some minor revisions but everything you need to duplicate this project is included there.

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