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 »

Thanks John! Was missing the key word octal, was able to find what I needed on eBay!
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Nicolas Krause
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Re: LCD Vacuum Sensor

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As we're in Christmas holidays I've gotten back to working on the vacuum sensor. I'm currently in the process of laying out the PCB in KiCad. There's lots of finicky details to work through to make sure positioning is correct but the broad outlay of the board is visible. The amplification circuit and connector to the LCD in center, the two 20 pin connectors to hook in the microcontroller board,and on the left a 4 pin terminal connection to connect the wires to thermocouple gauge.
Capture.PNG
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Nicolas Krause
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Re: LCD Vacuum Sensor

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Routing on the board is now completed, I still have to pour the ground plane and place some mounts if I want to put it in a case but progress is progress. I'm never 100% sure about how to route things well, but this is a simple circuit so I don't anticipate too many problems.
Capture.PNG
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Nicolas Krause
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Re: LCD Vacuum Sensor

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Capture.PNG
The routing is now complete and all that's left to do is send it off to the board house!
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Richard Hull
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Re: LCD Vacuum Sensor

Post by Richard Hull »

Great work and workaround on getting the sensor data into a computer or data collection and reporting scheme. Sometime we latch onto free stuff or stuff so cheap that to get it to do what we want it to do takes a lot of time and effort to fit it into our needs instead of a lot of money spent buying something ready to go. In doing this, we pick up a lot of learning in the doing. Just another skill under the belt....Ata boy!

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Nicolas Krause
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Re: LCD Vacuum Sensor

Post by Nicolas Krause »

I'm just waiting on a relay terminal to complete this board, but I have finished most of the soldering and just have to do some final tests with the program to make sure it runs reliably.
signal-2021-01-29-201341.jpeg
signal-2021-01-29-201333.jpeg
Cai Arcos
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Re: LCD Vacuum Sensor

Post by Cai Arcos »

Is that the Art of Electronics peeking in the corner of the photograph?
Great project too, a really convenient way to measure vacuum!
By the way, have you considered optical isolation or, more simply, just using a usb isolator if you ever connect this to a PC? I feel it would be an easy way to protect your computer and limit the damage of a possible accident.
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Nicolas Krause
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Re: LCD Vacuum Sensor

Post by Nicolas Krause »

Good eye! Yes it is an art of electronics book (actually 2, 3rd and 2nd edition as the 2nd edition has some neat physics circuits at the back). The plan right now is not to plug the device into my computer but rather to use a USB power supply to run it. The whole board is built around a TI Tiva C Launchpad, which is a development board. At some point in the future I plan to add a logging capability so that I can plug it in to my computer and download the time series pressure measurements but for now its going to sit beside the fusor and give me live pressure measurements.
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Re: LCD Vacuum Sensor

Post by Cai Arcos »

Thanks for letting me know about the physics circuits on the 2nd edition, I have only read the 3rd and I am quite surprised by the amount of content that was removed...
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Nicolas Krause
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Re: LCD Vacuum Sensor

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Just reviewing the board as I run through setting everything up, and I've noticed that I've forgotten a potentiometer on the power supply to the thermocouple gauge. I'll have to complete another revision of the board at some point, but for the immediate I'll probably just cut the power trace on the board and bodge in a potentiometer with some solder and wire.
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Nicolas Krause
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Re: LCD Vacuum Sensor

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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

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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 »

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 »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Nicolas Krause
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Re: LCD Vacuum Sensor

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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 »

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Nicolas Krause
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Re: LCD Vacuum Sensor

Post by Nicolas Krause »

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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