Well, I've finally built the board and tested it, and everything was fine
UNTIL I got to real world:

One of the relays (the one intended to trigger the welding torch) brings in
these pretty 45 Vac into the circuit that stop everything. Taking away this
signal brings the circuit back to normal operation. What's the problem? This
45Vac are NOT in the PIC's path, they are in the relay contacts. Any
suggestion?

This is the circuit:

>

                                      O +V (unregulated) being 12VDC
                                      |
                                      |
                                  ----*
                                  |   |
                                  |   C              +-------------------o
                      1N4007     ---  C              |
                                  A   C relay coil     /
                                  |   C               /  N.O. switch
45Vac from the torch
                                  |   C              /   in the relay
                                  |   |              |
                                   ---*              +-------------------o
                                      |
                470      470        |/
 PIC  o----*- /\/\/\-*-/\/\/\-*-----|   BC337
           |         |        |     |\
          +++       ---      ---     V
      22K | |       --- 10n   A      |
          +++        |        |      |
           |         |        |      |
          ---       ---      ---    ---


                              ^
                              |
                           1N4148


----------------------
  Jaume Aragay Badia
   aragay@email.com
----------------------