It's been a while since I posted any updates on the Arduino THC project.

It's taken me a while to get the code working after I screwed it up by "cleaning it up". While I was working on getting it working, I started testing other features I had implemented. Unfortunately, it still isn't working as much as it was before I broke it.

I have usage trackign mostly working (all the parts that I could test). It tracks:
  • Pilot arc count (number of times torch was triggered)

  • Pierce count (number of times arc good signal was received)

  • Usage time on tip (hours, minutes, seconds)

  • Cutting voltage set point

In addition to updating the data, it will save it to flash after having been idle (not cutting) for a minute.

I've implemented a state machine to control the THC. The states it has are:
  • Disabled (won't pass through "torch on" signals)

  • Enabled (allows use of menus and goes to cutting mode on "torch on" signal)

  • Cutting (actively cutting and controlling torch height)

  • Cruise Control (monitoring cutting voltage and will set cutting voltage to the current value when the button is pushed)


The menu system is working, though not all the features are implemented.

I have the voltage monitoring "sorta working". I'm using the op-amp filter and the software is filtering the voltage readings using a sliding window average of 25 samples total, each taken about every 1 - 3 millisecond (sampled as fast as possible). The voltage value is displayed on the LCD every 25th sample.

It's not the best way to do it, but you can tell how stable the voltage is by how blurred the LCD display is. If it isn't being filtered well, it's just an unreadable blur. I've gotten to the point where it appears to be pretty stable at the 1 volt level (I haven't really been paying attention to the tenth of a volt part). While this may not be the most reliable way to figure out what's going on - it's the best I have right now.

When the pilot arc ignites, I get a good voltage display that is pretty stable. However, when it goes into cutting mode, the display goes to zero - which I'm sure is a software bug. My challenge is to try to figure out how to debug it without a debugger and without a serial port to dump data to (I ordered chips to opto-isolate the serial port, but don't have them yet.)

I'd like to figure out an easy way to debug this without using the CNC system. I could make a box to do it (power supply, switches, LED's and a potentiometer to vary input voltage), but would rather not spend the time. So, if I can't jury rig it, I'll have to do that.

I've also been looking at noise issues. The bulk of the noise is coming from the switching supplies that run the CNC interface, and the stepper controllers. I'm using this to power the Arduino. It's horribly noisy. When disconnecting the interface to the CNC and powering it on its own wall wart - the signal is much cleaner. I should be able to address that once I get the opto-isolators. That will let me use the wall wart and I can isolate the signals to the CNC and for a serial port to collect data.

I hadn't bothered to hook up a common ground yet as I didn't want to destroy anything with a ground loop. I did find that I got rid of a lot of noise by just connecting the chasis of the PC to the old computer chasis holding my motor controllers and power supplies.

I got a new oscilloscope for this project and I still haven't totally figured it out. It appears that some setting I'm changing causes the signal to appear to be much noiser (in spite of the LCD display showing that it appears pretty clean). I haven't figured that out yet.

At this point, I need to:
  • debug the "arc good" signal (I'm getting it from the PP50, but not passing it back to the CNC)

  • figure out why 0 volts is displayed while cutting

  • figure out why it seems to hang every now an then


Then, later this week I should have the parts to opto-isolate the interface to the CNC and a serial interface to the PC.