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

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