I have been experimenting with the LM331 and trying to get it to register in Mach.
I followed freedom2000's wiring schematic originally but think I missed something as I failed to get a frequency out.
I then built a v-to-f circuit ala National Semiconductors web page using 3.3v.
The output was in the neighborhood of 4khz if I remember.
Twisting the circuit pot would very the freq +/- 1khz. I did not very the input voltage as I just didn't go there yet.
I used the index input in ports and pins and was able to get a reading on the spindle speed calibration graph.
At this point I was fiddling with my breadboard wires and back fed voltage into a pin on the LM331 that I shouldn't have and poof! Trabajo no mas. I'm waiting no some replacements.

As an aside, I got an Arduino for Christmas and am trying to get it to work as a DTHC independent of Brains similar to the stand alone units.
Progress is slow as I'm new to C+. I've got most of the blocks down but am working on getting them to work together.

Hi jlindst and welcome to the forum

As an aside, I got an Arduino for Christmas and am trying to get it to work as a DTHC independent of Brains similar to the stand alone units.
Progress is slow as I'm new to C+. I've got most of the blocks down but am working on getting them to work together.

A while back I was working on an arduino DTHC however although I'm fine with digital electronics I'm not so hot at analogue. When it came to doing the plasma interface board I was cool with most of it but I was stuck on how to absolutely make sure no spikes got through from it and killed the arduino. I've put it on the back burner for now. If it's any use I've attached the basic sketch I used just to emulate the DTHC principal on the arduino. (You'll need to change the extension back from txt to pde to load it into the IDE. the forum won't allow .pde)

Cheers

Ian

Hi Stirling.
Thanks for the sketch.
On the analog side I was working of a variable resistance voltage divider coupled with an R/C setup. This way depending on what a given plasma puts out in tip volts can be adjusted to fit within the 0-5v window that Arduino requires. I'm also waiting for some parts (including a new LM331) to build a voltage suppressor as to hopefully not feed the Arduino more than it can handle,

What I've got to date is a smoothing sketch to average the analog inputs.
I've got a comparator sketch similar to yours to manipulate up/down function.
What I'm working on now is getting a tip volts reading to send into the MACH DRO (1036?) for adjustment purposes.
That part I'm having trouble with is getting arduino to split it's output into 2 serial channels. (SoftSerial is what I'm working with to do the split)
One for the 0-1023 up/down comparator function and the other for tip volts.
I've been playng with the modbus slave sketch to get the serial based tip volts to the DRO.

Hi jlindst - you're further down the road than me so good luck. I will get back to it though when I have time.

Cheers

Ian

Im interested that others are looking down the route of using a plc, i looked at this, in simple terms this is what other thc systems use, an external processor to do the thinking and tell mach what to do. The reason i decided against it, and i got as far as buying the plc, is that i found mach would do all this for me if i used a brain. Critics of the system say brains are slow, thats maybe true but i still think they are fast enough for this application, more of a limitation is there is no ability to make a p i  d loop, also you have to get an analogue value into mach. I was/am using a pokeys to do this, the analogue input is less than great, the value wanders quite alot when the voltage is constant. I was planning on using a g100 for this instead but after spending ages changing my machine over i had huge problems with the g100 so had to abandon it. Maybe i should revisit this, maybe through using buttons in mach i could enable/ disable the plc with connections and raise and lower the target voltage in the same way, i just dont really like the two screens and input buttons etc, its just ugly.

As far as interfacing with the plc goes using the voltage divider there should never be voltage spikes formt he plasma cutter larger than the maximum voltage of the transformer unless they are noise, so if you can fire into free air and not cause a problem with over voltage to the plc surely voltage spikes will simply give an erronious reading??

Eureka!
$27, about 120+- hours of staring at code and about 2 dozen cappacuinos = DIY DTHC over USB.
My widget looks like robot guts but the torch goes up and down and makes really purdy cuts.
Runs in Mach via da Brains.....BRAINS!!
Almost have it setup in EMC for the Linux set. (Why are you reading this forum?)
Thanks to Matt for the inspiration.
I'm working up a how-to and eagle schematics but this is the blueprint.
Tip volts --> BRD --> Volt. Div. --> Trans.Volt Sup. --> Hi freq gap --> RC filter/conditioning -->
PLC(10 bit ADCx3 sample) --> Modbus encapsulation -->Modbus RTU -->brains...Brains... BRAINS!!= Zup and Zdown releative to Tip volts.
ArcOK and trigger relay are piggybacked as well.
Electrons are fun. BRAINS!!

Hi jlindst - nice one - good work. I've been tackling this in a different way with the arduino. In my scheme the arduino takes full control of the Z during cutting and so far I'm getting good results but I'm currently simulating the arc voltage so I know I'm only ever feeding the ADC with 0 to 5V. I need (like you) to make sure I get a safe, clean, 0 to 5Vdc out of the plasma unit and that's the bit that's holding me up at the moment so can you give more details of your interface board.

Also regarding ArcOK, on my bought in THC300 unit this used to be done with a current transformer, but in my kit it has been replaced by what looks like a snap-on ferrite core but with three wires attched, that clips round the earth cable (from the table/work clamp) inside the plasma unit - any idea what this component is?

Cheers

Ian

Hi,

I am new to this forum and have been reading the comments made about THC in Mach3.

I am an electronic engineer and building a Plasma Table for in house operations.
Since the info about THC in the Mach3 documentation is weak at best, I thought I would state what I believe I have figured out, then let others here verify my assumptions.

Once all is understood I will design a solution that uses Mach3 the most economical way.  Please make any comments to my statements here to help!

1.  It would appear that Mach3 has all the controls needed for THC via: ARC OK, THC Up, THC Dn and Z axis Home (for floating head) inputs to the Par Port and Torch On output.
2.  It also appears that in order to get to these signals and provide 4 axis of control for dual X, Y, and Z you will need a second Par port.
3.  In addition, it supports DROs for Z Axis position and Torch Voltage if the data can get into Mach3.  Any others required or desired?
4.  If Mach3 is controlling the Z axis as normal via the first Par port, the additional signals THC up and THC down are injected into the current position known by Mach3.
5.  To close the Z height control loop, using a Brain is slow due to its update frequency, so the control loop would be better if outside of MAch3.
6.  What is the preferred way to get the DRO information into Mach3?  Modbus or USB?
7.  The Torch Arc OK  and the Torch On Command are usually dry contact closures.
8.  The Torch Voltage signal from various Plasma Units will vary across a large scale and should be isolated for safety.

This is a good start, please comment and we will go from there.....

Thanks in advance,
Steve

Hi all,

It's a long time since I have not posted here  

I have practiced a bit on µcontroler since this summer, and thus I plan to give up my original design (with LM331) for the benefit of a simpler and more powerfull Pic based circuit.

I plan to use a PIC 12F675 (2 $) to perform the following functions :

- output torh up and torch down
- output torch OK signal
- input torch intensity (with hall effect sensor) (use Pic comparator to convert it to torch Ok signal
- input torch voltage through a voltage divider into the Analog to digiital Pic IO and elaborate the UP/Down outputs

As you can see all outputs are opto protected
the torch ON signal is sent diectly via a relay to the plasma (not controled by my electronics (also I could as there is one input left opened !)
I plan also to use the original Port 1 of my PC assuming that there is no need to add an extra one...
Why ?
Just because :
- I can put the extra Zero Z torch in serie with the X, Y, Z limits switch of my CNC
- I will not input the torch voltage to Mach3

The software will do the following :
- monitor the torch intensity and wait for "torch OK"
- if torch OK :
   - waits a few seconds for the voltage to stabilize after peircing
   - monitors the torch voltage and use it as a reference
   - loops on voltage measure + average (filtering) and outputs UP/Down signals
until torch NOK

Assuming that the Gcode is OK the height should be correct after peircing and consequently the first monitored voltage could be used as reference
There is thus no need to have the Voltage provided by Mach3
Also the upper and lower limits for generating UP/down signals could be generated by the pic

For the Torch OK signal I plan to use a cheap and very simple hall effect sensor UGN3503 (made by Allegro)
It is a "stand alone" device which only needs +5V power supply and outputs directly a voltage deviation from 2,5V reference if a magnetic field is seen by the sensor.
It can be used with a toroid to sense current in a wire



The toroid is extracted from an old PC power supply and a slice of it is removed with a dremel. It acts as a magnetic field concentrator into wich is inserted the sensor.
See how small this device is compared to a USB key  



And finally the virtual PCB  



Hope all this will work !

JP


-

Jp - i like it, the only thing im wondering about is the polarity of your plasma voltage, my cutter is negative polarity, if yours is you need to connect your voltage divider to vdd not vss, so the arc will pull the voltage down.

Steve- I replied to your post a while back but it doesnt seem to have got there, i will write it again when i have a moment.