[patriciooholegu]

Here is another question:
Since my firsts test with cnc boards (Always diy or savaged, mostly from copier machines) I plug the step-dir-enable pins on the boards DIRECTLY to the computer parallel port. I know this is not recommended and I didn’t suggest to any one, but for my low budget kind, and my profession (computer expert) it was on the beginning more chip and easy and fast to risk some of the many unused old computers I have, than to spend almost half salary on a breakout board.
Now the question:
Pic microcontrollers are some kind of isolation between pc parallel port and stepper driver board? I didn’t say optoisolation, because there is not any protection based on lights. But if any thing will blow-up, will be the pic (us$3 in my personal store) and not the computer (Which is not expensive, because mostly are build from savaged things) but yes a more powerful machine and therefore with bigger currents than the driver (Bigger explosions)
So, what do you think?
Last week I made the mistake of plug-in step onto ground and the poor 16f84 start to make smoke,not the computer, so that make my think about it.
Sorry about my English.

[Al_The_Man]

There is absolutely no reason why you cannot interface a PC to outside electronics without using isolation, it is done all the time.
The secret is to do it correctly.
Many of the high end industrial systems start out with 5v logic and processing and progress to 24vdc I/O and on to 120v/240ac controlled devices, all being referenced together, This is commonly done with earth grounding and bonding.
PIC micro's do not in and of themselves offer isolation, it requires devices such as opto-isolators.
Al.

[Larken]

The Pic can read directly from the printer port (step/dir) but doesn't have the current to drive a printer port (limits, Estop). You need a drive like a 74LS240 that can output more current. The Printer port usually has 150 ohm pullups and its too much for a pic.

You should always use buffer chips around a processor to protect it from noise which can cause damage and crashing. Also you should put 470 ohm pullups to all output pins coming from the parallel port.

There are a cnc boards that only have a processor with no buffer chips, and if you look at the forums, you will see people complain about freezing and problems.


Larry K