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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LCD Vacuum Sensor

Post by Nicolas Krause »

To use my thermocouple vacuum gauge and to continue improving my embedded development skills I've been working on programming a TI Tiva C Launchpad via the MeCrisp Stellaris language to read a value from the vacuum gauge and then print the value to the screen. It's been slow going, as I'm new to Forth (MeCrisp Stellaris is a dialect of it), but tonight I finally was able to get the pins outputting SPI signals so that I can communicate with the LCD. In addition I figured it was better to break this off from my main thread and start this smaller one. I plan on documenting the development of the program, pcb and final product here.
IMG_1095[1].JPG
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Richard Hull
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Re: LCD Vacuum Sensor

Post by Richard Hull »

If I didn't have so many TC gauge meters and readouts with mating gauge tubes laying around the lab, I would make one up using the Arduino Mini-Pro and backlit I2C LCD readout. The TC gauge article in an older Bell Jar gave hard non-linear data points all along the pressure vs. voltage outputs from several different common gauge tubes. With a lookup table and interpolation math in the program such a project is very doable for any micro controller.

The BJ article should be on the BJ website.

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 »

If I were in your position I probably wouldn't be doing this either Richard! But I'm learning a new programming language, I have a design in mind for the PCB that I quite like, and I think this will be a very nice little project. The first goal of this whole Fusor project is to learn, and this is helping me do that in spades. By way of an update today I was able to get the LCD to turn on. I'd initially miswired some pins, and I had to determine the configuration sequence but all is well!
IMG_1096[1].JPG
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Richard Hull
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Re: LCD Vacuum Sensor

Post by Richard Hull »

I have always done a ton of useless projects just so I could learn something new and put it into practice so that from that point on, I would own that possess and knowledge for life.
Doing anything that seems useless to gain and possess knowledge is always a good thing.

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 »

Just a quick update here, I've decided to swap out the screen for a simpler text LCD. I was looking at the programming task ahead of me, and it required writing some graphics drivers for the dot matrix LCD. Rather than struggle with that task in a new language, I figured it was better to go for a simpler solution so that I could crack on with other problems. The replacement screen is on its way and I'm currently in the process of configuring the ADC on the board to take a voltage measurement from the circuit. I appreciate you posting all the Bell Jar newsletters here Richard, always good to read, especially the latest issue with its description of a turbopump controller, my next project!
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Richard Hull
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Re: LCD Vacuum Sensor

Post by Richard Hull »

I am with your Nicolas. I have used only the arduino and the massive library group of custom apps assembled over the years at arduino.cc. It is so useful to grab a suitable special function library that 80% of the tough work is already done for me by folks a lot smarter than me. I built a TFT GM counter the TFT screen took me one week to work out well. It was not worth the effort. I have found that a nice library exists to effortlessly use backlit 2X16 and 4X20 LCD displays as well as the I2C organic LED displays (oLED), that reduces the effort to just spilling on the desired text and various computed data results as numeric data. No line of cell counting needed to place the text or data. The arduino is very well suited due to its long history and numerous free libraries. The IDE is easy to use and learn as it is a variant of C.

Folks who like to play fancy custom graphics can have at it with the TFT displays. To my way of thinking if you plan on making 1000 pieces of a custom system, then the time might be well spent. Me, I just want an easy to use and easy to implement readout of plain text and data.

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 »

Happy to report, that without too much trouble I can now write text out to my LCD screen. It took a solid 8 weeks for the parts to arrive due to mail delays with the pandemic, and since completing my coop and moving back home I haven't had much spare time to work on it. All the components of my program now work individually, I can read values on the ADC, write out values to my screen. I just have to confirm that my amplifier is working properly, and then I can begin to work on my PCB design.
IMG_1149[1].JPG
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Nicolas Krause
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Re: LCD Vacuum Sensor

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Happy to report progress continues quickly, I've written a little function that updates to the screen. It converts an int value to a series of char values and prints them out. Forth is a fun little language!
IMG_1154[1].JPG
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Nicolas Krause
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Re: LCD Vacuum Sensor

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I've got my amplification circuit with a bit of spare time this past Saturday. I'm now looking at designing the PCB for the gauge, I've googled this a bit, but is anyone aware of the type of connector/plug use for vacuum thermocouple gauges? It'd be quite handy just to be able to order one from a supplier like digikey and make my own cable. Failing that I've been monkeying with the idea of designing a discrete PCB that would connect to the device that I could run wires from myself.
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Re: LCD Vacuum Sensor

Post by John Futter »

Most of the thermocouple gauges use the octal valve (tube) plug on them so you will want the octal valve (tube) socket
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Re: LCD Vacuum Sensor

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

Post by Nicolas Krause »

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

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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
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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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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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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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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

Post by Nicolas Krause »

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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