Disposable pci LPT port or isolated ($) breakout board ?

[CanSir]

The Cambell Design BOB+ looks like an excellent piece of kit, but I'm really tempted to "save" myself approximately $115 in startup costs by buying a disposable $15 PCI parallel port for now. Will an add-in parallel port card serve as a sacrificial barrier or is my PC still likely to fry if I should accidentally wire something incorrectly?

BTW I know the BOB+ offers more than just optoisolation, but in an effort to keep costs down on my CNC project, I'm trying to avoid adding on all of the bells and whistles out there.

TIA

[Richster]

That one's up to you really - depends how confident you are in your electronics skills. For what it's worth I am using the PC's built in port and my own opto-isolation (there's a circuit diagram under the Xylotex forum). Provided you don't short any of the parallel pins (i.e. always make sure there's a substantial resistor between the pin and 0v) I think the risk is actually quite low. Also make sure your circuit board is mounted on nylon standoffs and is enclosed so there's no other danger of shorts.

I haven't fried anything yet **touches wood**

To answer your question - I think you'd have to try quite hard to damage your PC if you destroy an added parallel port, but I guess it's possible...

[CanSir]

Thanks! I think I'll give the disposable parallel port card a go. I got the computer I'm using for controlling the router for free so shelling out $15 to maybe protect it from getting fried is money well spent. Naturally I will try to connect everything up right the first time.

:-)

[Richster]

OK - good luck!

For limit switches you can connect directly to the port via pullup resistors, but from my own experience I'd really recommend the isolation route for both the protection it offers and to prevent electrical noise reaching the parallel port. The additional components really weren't expensive.

Also, if whatever controller board you have has the option of enable/disable switches on the stepper drives, I can really recommend this. I often 'trial' run stuff switching off both the Z axis and the router control, which allows me to run just X and Y movements in a relatively neighbor-friendly way. Mach 3 does have a 'Z-inhibit' button, but on more than one occasion I've had that axis move even with this turned on. Can't explain that one....

[jalessi]

http://www.embeddedtronics.com/breakout.html

[Richster]

Cheap indeed, but doesn't offer any form of isolation from what I can see. However this is probably a convenient way of connecting to the 25 pin port which is a little fiddly otherwise.

[ger21]

How about this one.
http://www.embeddedtronics.com/opto.html

[jalessi]

Gerry,

Good call and a mouse click away. How rare.

Jeff...

[bsd_mike]

Here is one more:
www.chaski.com/opto

No breakout, but you can configure the ports however you want.

It does require a fatter pulse width (25 us).

[TOTALLYRC]

Originally Posted by ger21 How about this one. http://www.embeddedtronics.com/opto.html

If I read that correctly, you just get a bare pc board for $15. What does it cost to get one with all the components installed?

Mike