need help deciphering circuit for foot control.
I'm going to build a pedal for my tig welder and am having trouble with a modified circuit I want to try. I've deciphered the 'simplified' circuit by now (pg.3), but would like to build the more complex one. Basically the one on page 4, I assumed the author meant for the builder to provide new headers, but where these connect to I have no idea.
The description is as follows:
Here is an update to the 91811 schematic. This
contains the OEM version of the machine [pages
1,2], my original modification for external heat and
timing control [page 4], and a substantially simplified
circuit providing external heat control alone [page 3].
This simplified external heat mod involves no surgery
to the control board. Tie-in to the PWM controller
is achieved by disconnecting the 3-pin connector from
the existing front panel 10K heat pot and routing it to
the board containing the added circuitry. This board
will supply it's own 3-pin cable/header which will then
connect to the original 10K pot PCB. The worst of
the modification is extracting GND and +12V from the
main board which can be found on the voltage
regulator U5, at pins #2 and #3 respectively. With
some soldering skill one should be able to make the
two connections without needing to unmount the
main PCB from the heat sink.
What I can't figure out is if the 'timing' he refers to is to control the 'shielding gas solenoid' or the heat timing (like some sort of pulse control). Also, the pedal I want to retrofit only has 15 degrees of motion on the pot, however I don't think this presents a problem since I'm guessing the signal is amplified; however, should I worry about the pot reading '0' ohms at any given position or is it ok for it to read some 'low' and 'high' value relative to one another?
To conclude, I read somewhere that this modification somehow takes care of interference that may be caused by the machine operating (dunno how); so my concern is can I build the circuit inside the pedal (extending whatever leads to the machine [will shielding be required?]) or should I keep the circuit near the machine?
Any and all help will be very much appreciated.
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