I used another PIC 12CE518 (including EEPROM) to generate the function of 2000 Hz clock necessary to control under interruptions the cutting software. (only one component thus can make the work of a handle)
With the advices of several active members of CNC@net list (thank you Gerard, Michel, Jean-François and others...) new functionalities went to enrich the program in the PIC. The final issue of the PIC's software, called PICACHOF, also deals with all the functions of management of the heating of the wire.
PICACHOF :
The overall diagram shows very few components. It includes:
- a 5 V power supply function built around one traditional 7805
- a timer function, interface to the PC, management of the manual heating and regenration of the heating signals coming from the PC ( all this been inside the PIC 12CE518 programmed in " picachof ". The source is available here: picachof.c as well as the corresponding HEX: picachof.hex
- an interface to the hot wire power supply controlled by an optocouplor driving a mosfet.
It exist a PCB, but, as far as I know it has not yet been tested ! So it's up to you to verify it ... you can download it here : PCB_PICACHOF folder. It includes 2 JPEG files (pikacompo and pikacuivre) that printed at 600 Bpi will provide you with the copper side and the components side. There is also a PCB.ZIP archive giving all informations needed to build another version of the hardware where the stepper motors interface is performed by a dedicated integrated circuit.
functions and instructions of picachof:
GP4 and 5 outputs present a rectangular signal at a frequency 100 time lower than GP2 (20 or 40 Hz according to the selected frequency see after).
The cyclic ratio on GP4&5 is adjustable between 2% and one max value (typ 98%). It is this variable cyclic ratio which, via the optocouplor and the mosfet, will heat more or less the hot wire.
The manuel/PC switch connected to (GP0) is used to select the configuration manual or PC. If PC mode is chosen, GP1 input receives the heating signal generated by the PC. This signal is amplified and is presented on GP4 and GP5 exits.
A filtering is carried out to limit the value of heating if heating from the PC is higher than the authorized max value. If heating by PC is blocked at one, the heating sent to the mosfet is set to zero.(but not the value provided in return to the PC)
At the first bootstrap, the percentage of heating is, I think, a 100%. It is thus advised not to connect the wire during the first test! The value may be decreased (resp.increased) while pushing on the MINUS (resp. PLUS) buttons.
By default, maximum heating is limited to 98%, one can memorize a lower maximum value of heating after having selected this max heating up to the desired max value, while pushing on the 2 buttons simultaneously.
One can come back to the maximum value of 98% by pressing the PLUS button MORE during bootstrap (switch off then ON the the IF power supply) the swich being configured in position manual heating.
The last manual value of heating used, is, of course, stored to be selected at the next powering...
Lastly, at boot, if the MINUS button is pressed (in manual configuration), the clock frequency passes from 2000Hz to 4000Hz and vice versa and is memorized.
connection with the PC:
The connector to be welded onto the PCB is a subD 25 MALE. The cable connecting the interface to PC is simply a point-to-point extension cabl*e between two connectors a male, a female.