opto-isolator/optocoupler for parallel port

[podolskiy]

I am planning on building my own CNC machine from scratch.

It will likely be a rack-and-pinion based CNC mill employing a dramel or some other light-duty router with variable speed adjustment.

The tool would move above the workpiece. The worktable would be about 1mX1m.

Weather I would use a self-developed PIC controller or I would use the 'driver chips and bridge controll chips', I want OPTOISOLATION of my circuit from my computer just in case. ( I want all 17 pins or at least 16 to make it even )

I am not sure if controll pins are used for one way or two way communication, but i doubt it. They are labeled "clock" "cw/ccw" this is what makes the motor step, obviously.

I am loosly basing my design on the "CNC robotics" by geoff williams, and he recomments the optocoupler, but has resistors do the job.

How can I build that part of my circuit?

Thank you.

[Al_The_Man]

Originally Posted by podolskiy I am loosly basing my design on the "CNC robotics" by geoff williams, and he recomments the optocoupler, but has resistors do the job. How can I build that part of my circuit? Thank you.

Look up the data sheet on the opto you want to use, e.g. 4N35 and see the current rating for input and output, the resistor value will be calculated based on the voltages used to achieve a value that will design for somewhere in the mid current range.
It also depend on how much current you have available to drive the opto from the P.Port.
If you connect the opto to the port, use the output in the sink mode, rather than the source mode.
Al.

[podolskiy]

I will, thank you for that.
What is a sink mde and source mode?
Is that pn the ground side and the power side? Keep hearing this term, but had never seen it.

The hFE and minimum opening voltage of the transistor isn't told in the datasheet.
Do I need to know that to select the right resistor?

[Al_The_Man]

Sink Source.
Al.

[TarHeelTom]

Haven't read that particular book, but have read the sample pages available on Amazon.

Please understand that he probably built that router at least 8 years ago, which was kinda the dark ages in diy cnc.

Things have come a long way since then. Mr Williams was forced to build everything yourself. In the interim a lot of good engineers have developed more or less standard components to build a lot of components that Mr Williams was forced to build himself, as there was not choice.

You're tallking here about building a BOB, or break out board. There are lots of good break out boards on the market out there which really simplify the process of getting the signals to and from the computer.

I'm not suggesting that you can't or shouldn't do it yourself. Heck, you could go start your own copper mine and smelt the copper and make the wire yourself, then build a stepper motor factory and build the steppers yourself.

What I do suggest is that you go to the websites of several of the companies which build BOB's (for example) and read their technical literature. For instance, go here: http://www.pmdx.com/PMDX-132 and download their technical manual for several of their bob's. One thing you can learn here is which pins are commonly used for input to the computer, and which pins are commonly used for output from the computer to your system. Actually, I'm under the impression that on a pc printer port, most of the pins can be used in either direction.

Another consideration is opto-isolation. Many of the better motor controllers already have the opto-isolator built in, and you generally don't want to duplicate it.

You're also going to need some software to run the machine. The two most common programs are Mach3 and EMC2. Mach3 has good technical support, as it is a commercial product. EMC2 is a solid product, as it was built by the military. Anyway, reading the docs for EMC2 can be a real eyeopener, as they give you a good idea which pins can be used for what.

One thing that helps on this forum is to ask intelligent questions. And doing your homework reading really helps to make your questions intelligent ones.

I realize that I may have answered more questions than you asked, but I do tend to run off at the mouth. (Now, where'd I put my rabies medicine?)

Good luck on your build.

Tom

[podolskiy]

thank you very much

i will
(right now i am busy building a PIC programmer board)