Plasma Table Arduino THC: Board Overview
ฝัง
- เผยแพร่เมื่อ 30 มิ.ย. 2024
- Upshot: A thorough look at the PCB for my Arduino based torch height controller, for my LinuxCNC plasma table build.
Topic index:
00:00 - Intro
02:54 - Tips on designing, building & KiCAD
06:52 - How a THC works, my Hypertherm, voltage dividers & adjusting for your plasma
12:30 - RC lowpass filter, Thevenin's theorem & picking a capacitor
21:05 - Other components (linear regulators, power supplies, and optocouplers)
30:12 - A couple notes on not breaking your stuff/electrocuting yourself
32:17 - Potential improvements, other quirks, stuff that didn't work, stuff you could change
44:24 - Digging into the wiring/schematic, LM317, PC817
66:33 - Looking at the PCB layout & finale
Here's a permalink where you'll find the schematics shown later in the video. Note that updated versions may be available if you check the latest version of the repository.
github.com/swolebro/swolebro-...
The latest version of the repo, with extra LinuxCNC stuff and more:
github.com/swolebro/swolebro-...
Here's the full plasma build series:
• CNC Plasma Build (Full)
Just Arduino stuff:
• Arduino
Your donations help me make more cool shit:
paypal.me/swolebroshopworks
Other TH-cam channels:
Contextual Electronics: / contextualelectronic
CE's Getting to Blinky 5.0: • Getting To Blinky 5.0 ...
EEVblog: / eevblog
All About Electronics: / @allaboutelectronics
Some wiki links (blame TH-cam for automatically inserting the awful URL redirects)
en.wikipedia.org/wiki/Ohm%27s...
en.wikipedia.org/wiki/Resistor
en.wikipedia.org/wiki/Voltage...
en.wikipedia.org/wiki/Low_pas...
en.wikipedia.org/wiki/RC_circuit
en.wikipedia.org/wiki/RC_time...
en.wikipedia.org/wiki/Cutoff_...
en.wikipedia.org/wiki/Th%C3%A...
en.wikipedia.org/wiki/Network...)
en.wikipedia.org/wiki/Linear_...
en.wikipedia.org/wiki/Opto-is...
en.wikipedia.org/wiki/Operati...
en.wikipedia.org/wiki/Operati...)
en.wikipedia.org/wiki/LM317
A RC lowpass filter calculator:
sim.okawa-denshi.jp/en/CRtool.php - วิทยาศาสตร์และเทคโนโลยี
Great video thanks for the very good explanation on how the ride hight works
This video and accompanying notes earned you a sub and a like. Thank you for your attention to detail, and especially all the links in the notes.
SUPER informative! Thank you VERY much for sharing your knowledge and experience on the THC.
Excellent work. Long live the open source.
Nice job I am going to use a Attiny in place of the Arduino and move the Arduino to behind the optoisolators so I can have the Arduino connected to usb as well.
Thanks for posting this, I've been thinking about diy thc's quite a bit lately, if I ever end up building one, this will be very helpful.
I've got a question about the input voltage sample from the plasma, would a 5.1v zener diode between the input voltage and ground provide adequate over voltage protection? Or, would that introduce a whole new set problems?
Hy, did this setup work well on long term ? i guess you have used it a few times since the video was posted, if it does work as intended, why are commercial THC modules like Proma compact soo expensive compared to this setup which is pretty simple and cheap, does they offer something extra ? The input voltage from plasma, if it doesn't have the output divider, can be taken from the ground clamp + torch wire and step down ? also in Proma THC which voltage needs to be input, divided or directly high V. Ps very nice explanation in the video!
I have some calibration questions. I'm trying to calibrate the THC and no matter what it set the pot to the torch goes down as it cuts until it collides with the work. I have all of the THC % and corner lock features working in linuxcnc.
I don't know what values to change in the code. It's hard for me to find documentation on what my plasma(Hypertherm 600) puts out for voltage. I measured about 230v raw and I made a voltage divider at 56:1. I'm not sure what's going wrong.
What exactly are the minset and maxset? What do the values mean? are those values in ADC?
Thanks.
Hi, Swolebro, very good explanation, please ask me a question: in your project, does the plasma power supply need to have a voltage divider?
Yes, the Hypertherm I have puts about 135V in normal operation, and up to 300V peak, both of which are far too high for an Arduino. Luckily, there's a 50:1 divider built in, which brings the voltage to a very usable 0-6V range.
If yours doesn't have a voltage divider built in, that is DIY'able too. There are some videos around on here of people adding them to various off-brand or no-brand models.
@@swolebro can you share one , cause I'm having a hard time with the divider and the hf start which keeps resetting my Arduino
@@chebhou He explains it at 10:30 you add 2 resistors and read in between them.
Hi, watched your video. On your Voltage Reference point. A better way to do that is with a Voltage Reference IC. Fewer parts, they don't require adjustment and are reasonably accurate at the "entry" level. For 5V MCUs, I like 4.096V refs as each count is 1 mV. Just adjust your divider so full scale is 4.096 volts.
The Arduino Nano (ATmega328) only has a 10 bit ADC, but I see how the math works out with 4.096V... I like that. Very clever.
And yes, in hindsight, I guess a voltage reference could be used in place of the LM317 here, and then it would save you from futzing around with the extra 1% resistors. If/when I get around to taking another crack at this, I'll look into the options for that. Is there a ubiquitous part you'd recommend? I originally used the LM317 since it's well-known, cheap, and the ability to set the voltage with the resistors lets me bumble through it when I'm doing first-pass development on stuff like this/etc.
@@swolebro.. Not sure if it is what you are looking for but the lm431 is often used to set a voltage reference
THANK YOU FOR YOUR PROJECT...YOU HAVE SCHEMATIC VOLTAGE DEVIDE?
be carreful if you want to make voltage divider, i burning my avometer, one monitor and one pc
Another question If you dont mind I see on the frawing you are holding it is written 2Kohm but the the schematic it is written 200 and 510 ohm am I not seeing it correctly?
The 2kOhm in the drawing is part of the internal voltage divider on the plasma cutter, whereas those two resistors on the board are for setting the linear voltage regulator output.
My plasma cutter has a 100kOhm and 2kOhm divider built in, which scales down the torch voltage ~50x, from 0-300V to 0-6V. The values of those resistors aren't really important, so long as your torch has a divider that puts the output in a not-gonna-fry-an-arduino range. If my plasma torch didn't have that already built in, I could build a divider with a 50kOhm and 1kOhm resistor, and it would have the same ~50x scaling effect.
One of the wiki links in the video description is the article for voltage dividers.
The LM317 just uses two two resistors to set it's output voltage, and we use that as our stable reference when measuring the plasma. Those values were picked to give a reference less than, but near to, 5V.
Turns out the LM317 has a wiki page of it's own with the wiring diagram: en.wikipedia.org/wiki/LM317
VERY GOOD VIDEOS. THANKS FOR SHARING
CONSULTATION. THC OUTPUT IN WHICH PIN DO YOU CONNECT ON THE DB25-1205 BOARD?
That totally depends on how you configure it. Check out videos 7, 8, and 9 in the HAL tutorial series: th-cam.com/video/8tMgeA0iWn4/w-d-xo.html
The other videos in that series may be helpful too, particularly if you aren't experienced with HAL yet.
@@swolebro Thank you so much
now i watch the videos
greetings from Argentina
Hi buddy, (it is difficult for me to explain since I do not know English) you can ask a question if you do not mind, I have no voltage divider on the plasma then how to assemble the voltage divider to work with your Board ? Thanks
Eh, if you do need to add a voltage divider to your board, you're getting into some potentially lethal territory. You'd need to open up the casework of your plasma cutter, tap into the leads for the torch and work clamp, and put those through the divider.
You're really gonna want to look for a wiring diagram and an electrical engineering student to help with that part. The raw arc voltage is easily in excess of 100VDC, with more than enough juice to kill you. Definitely don't go poking around in there with the machine plugged in (and even after unplugging it, wait 10-15 minutes for any internal capacitors to bleed down).
As for the voltage divider, you build a simple one of those as an educational demonstration.
Get a 9V battery and a handful of resistors from 1kOhm to 100kOhm. Grab any two of them, hook them together, and put the free ends on the battery terminals. Now read the voltage between where the resistors meet, and the negative battery terminal. Try a few different combinations of resistors and see how it changes. It should follow the V * (R2 / (R1+R2)) law from this wiki page:
en.wikipedia.org/wiki/Voltage_divider
The divider for the plasma is the exact same principal.
How would I change the code so the arduino outputs a step and direction signal to control a stepper motor driver? I'm very new to doing any actual programming other than changing values I can easily identify and reassigning pins. I use grbl to control my DIY plasma table. Works good if metal is flat, or I use a drag tip and floating head. I have another arduino based THC designed by another youtuber that works, but it too uses a separate arduino to control Z axis. It was designed as a standalone unit which I used diodes to allow my grbl to control Z until torch fires, then the THC takes over the Z axis. Your design is more of what I would like, turn a knob to set voltage instead of using a touch screen that has response issues at times. Wish I knew enough to integrate the grbl code and THC code into one and run it on an Arduino Mega 2560. I'm running grbl on a Mega with 3 TB6600 drivers off a breakout board shield for the mega. I don't have a good enough understanding of the code nor the time to really dedicate to learning it any time soon.
Hi, I was watching the video, but I couldn't figure out the value of the potenciometer, how much is it? Thanks!
any will do! :) just correctly map the voltage range to whatever value you want in the arduino code :)
hi there great job.... are you going to release a gerbel file... to make it easy to order pcb?
Not in the near-term. I'll get the whole project file (which can export gerber) out once I figure out the custom footprint issue, but I have other priorities (eg. covering the Arduino software sketch and Linux HAL).
tbh, if you're ordering from a boardhouse, you probably would want to redo the layout anyway so you could get it on a proper 2-sided PCB, organize it better, and fit it to an off-the-shelf enclosure. (Right now I'm using a plastic bag. lol)
in the schematic there are 3 pins that use db25. Where are the 3 pins connected? stepper motor driver or mach3?
thank you
I designed this for use with LinuxCNC and a parallel port breakout board, so those three pins would go to GND, and two (up and down) of the five input pins on the breakout, and then LinuxCNC can read them and move accordingly. My HAL tutorial series goes into that in much more detail.
I'm not sure if this THC would work with a Windows/Mach arrangement, since I have no idea how you'd feed it custom signals or turn those into Z moves without HAL (LinuxCNC's hardware abstraction layer). The Windows world is all a bunch of proprietary mumbo jumbo to me.
Can u give me the hal , and ini file for parport , i have a plasma , and having issue with config linux cnc , now i use qtplasmac , and are a loot of configs that i dont get thme how they are working .
Thanks .
ceramic caps tend to react much faster than electrolytic capacitors. would it be better to substitute a ceramic capacitor there?
If that's the case, then probably! Hahah. I'm no EE, so I'm just going by the analog fundamentals I learned in my physics undergrad, where everything's ideal.
"The difference between theory and practice is that in theory, there is in't one, but in practice... there is!"
I have re-laid out the board and while doing so noticed that the pot has no value given.
Also, would this unit be possible to operate on a Windows based machine, and possibly drive a Z motor driver without too much alterations?
Oh, you're right, I did miss the potentiometer value. Mine is a 10kohm, but in practice, the value shouldn't matter. The outer two legs to directly to AREF and GND, so the middle leg we're reading will sweep the full range, regardless of the pot's total resistance.
The only caveat to that is that you can't draw so much idle current from the pot that it makes your LM317 overheat. So, a 10ohm pot would be bad, but anything from 1k to 1M should work equally well.
I don't have any experience with Windows+Mach, but I expect that this would work similarly to how people use the Proma THC.
My next couple of videos are going to show how it works in LinuxCNC, doing a full tutorial on their Hardware Abstraction Layer. You can compare that to what you know about Mach and maybe grok the similarities/differences.
At the very worst, and old desktop to install LinuxCNC on and mess around with... costs like $50. The desktop I'm using is a decade old, only has 4GB of RAM, and has a 1st gen Intel Core processor. (They are now on the 10th gen.) It's worth doing just as cheap fun on a Saturday afternoon.
Here are two earlier videos going over the basic wiring and set-up with LinuxCNC.
th-cam.com/video/vR2xxRQQtyQ/w-d-xo.html
th-cam.com/video/8LVX380iDIk/w-d-xo.html
Then when you start learning other Linux-y things... just your basic commandline stuff, it sends your productivity through the roof.
(Last comment. Broke them up by topic since I wrote a novel here.)
In theory, having the Arduino control the Z stepper driver directly would be a matter of fudging the code where I set the optocoupler pins, and instead making it set pins for an external driver (as in any DV8825 tutorial). However, the difference between theory and practice is... in theory there isn't one, but in practice... there is.
I'd recommend against doing that for a few reasons.
Firstly, you're still going to want to optisolate all of outputs from the Arduino, to minimize risk to your driver. (Nice drivers ain't cheap.) Most drivers have STEP+, STEP-, DIR+, and DIR- pins, meaning you're going to need two extra optocouplers on the board. And, you'll need to make sure they're fast enough for handling your steps. I haven't tested the PC817's in that context, so you'll either need to test it on a breadboard, or do some guesstimations based on the datasheets.
Secondly, if the Arduino is controlling your driver, then Mach/LinuxCNC can't. Having multiple sources hooked up the driver means when one writes pins high, the other gets a bunch of current sent to a grounded pin. No bueno.
So, if the Arduino has full control on the Z, it's somehow going to need to know when to enable or disable THC (eg. during rapids), handle probing, etc. All without seeing the Gcode. I dunno. Seems messy and complicated.
With the way I have my setup, the Arduino tells Linux what to do with the Z, and the computer knows whether or not it should listen to that - ie. is the torch running, and at speed. Then since Linux is also processing the Gcode, it can still do lifts to a safe height for rapids, etc.
I figure Mach can work similarly, but again, I haven't used it.
@@swolebro Thanks for the detailed reply. You have covered several things I hadn't thought of.
Can i use the THC on my Arduino CNC Shield?
Do you have any idea as how this would compare to a commercially sourced THC such as a Proma THC which sell for about 300$?
I haven't got any experience with them, so I really can't say. You're always going to see some amount of seesawing as it continually overshoots and undershoots, and the degree of that depends on how much you smooth the signal from the torch. More smoothing means less seesawing, but also less responsiveness.
Usually I'm seeing about 0.005" of up-and-down seesawing, going by a little flag I have taped to my Z axis to visually watch the rotation. At least with this setup, you can tweak it until you get something you're happy with, whereas if you buy a thing, then you get what you got.
@@swolebro Thank you
hello I would like to know where I will connect pins 1, 2, 3 on DP25 1205?
That really depends on how you configure your HAL. The GND on the THC goes to GND on the DB25-1205, but the up and down pins can go to any two inputs, so long as you connect them to the thcud component in HAL.
For more info check out my HAL series, videos #7-9. The earlier ones might be helpful too, depending on how much HAL you know already.
th-cam.com/video/8tMgeA0iWn4/w-d-xo.html
Great, so there's no need to use opto isolators when using a Powermax 45XP?
What different on a PM45XP vs a PM65 that would make you say that? I'm not familiar with the differences on the XP series.
I will say there won't be any disadvantages to having opto isolators. It's about 25 cents in extra parts, but greatly reduces the risk of frying the computer.
@@swolebro Sorry, I meant for the arc voltage itself. I'm using the CPC port on PM45XP as an interface and are using an ACPL-790B-300E Isolation Amplifier to isolate the arc voltage from the controller board. The START and TRANSFER signals are handled by relays. I guess that your approach with a separate free floating THC controller board instead necessitates the opto isolators for the up/down signals when interfacing with the controller/computer? By the way, how do you set the THC voltage?
@ Ah, yes, if you have isolation amplifiers between the CPC and the THC, then that *should* be all the isolation you need. The key is to make sure your plasma ground and computer ground are not tied to each other.
Not sure if I mentioned it in this video or another, but early on while testing, I was stupidly using the USB serial connection from the Arduino to print debug information. Didn't take long until the computer told me it didn't like that. Hahahah. It froze up on me, but luckily didn't kill anything.
As for the voltage setting, I have a potentiometer and I do an Arduino analogRead() on it. Display the number on the LCD. Though honestly, with the homeshop work I'm doing, I just leave it on a mid-range value all the time. Keeps the torch from crashing and maintains a slight gap. Works well enough I can't be arsed to reach under the table and mess with it.
@@swolebro Thanks, then I fully understand your setup. I'm having the desired arc voltage set during post processing in Fusion360 and then the controller adjusts the Z-height based on the actual arc voltage. Or at least, that's the plan. I'm having some problem with the Marlin interrupt routines when it comes to Z-axis step motor control.
can it be connected to grbl?
On schematics , if u use 12v powering arduino u will burn ic .
This is a mistake , u have to use ony 5 max 5.5 v for powering arduino .
what is the voltage of the 10uf capacitor?
You mean its max rated voltage? Can't remember offhand, but it won't ever see more than 6VDC. It's nothing special.
@@swolebro many thanks for the answer I am not sure what voltage the capacitors need I have ordered the capacitors 1 uf with a voltage of 35v is the right ?what voltage must the 10uf capacitor have ?
hello! can you help me following your THC setup please. Thanks!
Any specific questions you need answered?
Is it possible to use with mach3?
i asked the same
Yes, you tie the contacts of the relays to the digital inputs on your Mach 3 interface board. You then enable the THC function of Mach 3 in the software.
does this need a voltage divider?
My plasma cutter has a 50:1 divider built in, which makes the output THC voltage typically about 2.5VDC. Absolute peak would be 6VDC, and if you hit that, something is already very wrong.
If your machine doesn't have one, you'll have to cobble that together before the THC inputs. Doesn't even have to be particularly precise, honestly. Once your THC is up and running, you just calibrate your machine settings to whatever cuts best for a given material and thickness.
@@swolebro 5: 1 is a good divider. anyway you put a 10uf capacitor on the input of the plasma, how many volts? and 1uf on trimport, how many volts?
@@swolebro are this build THC included sensor sensor?
hello
can you share me the code arduino ?
35:45 Well its not really works like this. If you are powering your arduino with VIN pin with voltage between 6.2 and 18V (there is 1.2V drop on regulator), that this voltages goes to 5V linear voltage regulator, something like LM7805. So no matter if you powering up your arduino with 12V by VIN, or directly with 5V by 5V pin, you getting Atmega328 (core of arduino) powered with 5V, so you still can read up to 5.5V safety. It is metioned, that you can read Vcc + 0.5V, beacuse you not really must power arduino by 5V. It can be 3.3V or any other voltage tolerated by Atmega328, however 5V is recomended beacuse of other components on the board.
Ah, the limit is Vcc+0.5V, not Vin+0.5V. That's good to know.
At least I've been lucky and haven't killed any more Arduinos. Did have one mishap frying a DB25-1205 pin from not properly isolating the ohmic sensing, but that's how you learn. lol
Oh, crap. Yet another pilot arc THC. It seems nobody has been able to make a THC for a HF plasma, which features an AC starting pulse with thousands of volts in both directions... :(
You'd have to do some research and testing yourself, but I'm betting this is a solvable problem. The circuit I came up with is extremely naive. Usually things like this would have inductors for filtering HF input, diodes for blocking current in the wrong direction, possibly some solid state switching to disconnect the Arduino from the signal during the HF start entirely, etc.
Start watching the electronics channels I mentioned. Take a crack at it. The worst you could do is blow $10 in parts and a weekend or two, but then you learn as you go.
And don't forget to share it when you're done!
Code arduino please
enough of the verbal diharea just get on with the actual project
You're welcome to go design one yourself, bud. You could even make your own videos for it.