Direct cnc connection or 2 pc mode? An overview.

1: Recommended operation mode / Empfohlene Betriebsart
PC 1: State of the art PC with Microsoft Windows and CncPlayer	Serial cable to connect PC 1 and PC 2	PC 2: Old DOS PC with FreeDOS and CncPlayer Client CPC	Parallel cable to connect PC 2 and the CNC machine	Your CNC machine
• The CncPlayer is your control center that let's you operate your CNC machine from. • Instead of a desktop PC also a notebook can be used. • Any 32 Bit Microsoft Windows OS like 9x, ME, 2000, NT, XP should work.	• The PCs are connected via the serial COM port. • Cable length of e.g. 10 meter is ok. • A special cable is needed. Take very care of the pin out pattern when you buy a ready made one.	• No hd, no monitor, no mouse, no keyboard needed. An old PC with a disk drive will do it. • Boot from a ready made disk. No configuration needed. • The DOS PC is fully remotely controlled by the Windows PC. • If you build your own CNC machine / electronic you might use this DOS PC as a case for your motor electronic and your power supply. That looks extremely good and is really low cost. Take advantage of the PC's power supply and drain the stabilized +5 Volt for your motor electronic.	• Plug your CNC machine in the DOS PC's printer port (or put a multi I/O card into the DOS PC). • Cable length must not exceed about 2 meter. • Take care of the pin out pattern. Printer cable do not necessarily work for your CNC machine.	• The term "Your CNC machine" refers to machine plus electronic! It is assumed that the motor electronic is in the machine's body or that an external motor controller is attached to your machine.

Instead of a big PC 2 you might also use a PC/104 single board PC. It's so small that it often fits into an existing motor electronic case or into the cnc machine's body.

2: Direct connection / Direktverbindung
PC 1: State of the art PC with Microsoft Windows and CncPlayer	Parallel cable to connect PC and the CNC machine	Your CNC machine
• PC must have Microsoft Windows 95, 98 (recommended), 98 SE or ME. NT, Win 2000 and XP will not work!

Yes, it is basically possible to directly connect your CNC machine to the Windows PC as shown above

• but that requires Microsoft Windows 9x. It will not work under NT, XP and such (please read the following fine print!).
  The CncPlayer runs on NT and such but when you actually try to send data to your CNC machine you'll get an Access Violation Error. As long as you do not try to access your machine everything will be fine. So if you have e.g. NT as your OS feel free to download the CncPlayer and have a look. As long as you do not click menu Action/Run and such you'll be fine.

Even if you have Windows 9x as your operating system your CNC machine will run jerky and sound noisy (if you have really low requirements you might live with it and find it acceptable).

"Why?"

Windows is not a real-time OS and its multitasking will suspend the CncPlayer often from work. That causes the jerks.

"But my movies play fine!"

Yes, but they work at a frame rate of 25 Hz (Pal) or 30 Hz (NTSC). A little delay of a few ms doesn't matter. The CncPlayer works at e.g. 10.000 Hz and much more, so delay matters.

"But product XXX from company YYY can do it!"

For money you get anything. With the use of a dedicated Windows driver (that runs in kernel mode) one can actually get much out of Windows and one can use it to directly control a CNC machine at an acceptable level. Though, device driver writing requires a lot of time / money. I have the skills to write CNC device driver and actually I have even finished one that works fine in experimental mode. But it's a long way from experimental level to end user level. Currently, I do not have the resources (time / money) for a device driver, so I put it on halt in favor of the "2nd DOS PC" solution.

I like this approach of a second PC because it is a technically fine solution

Better motor performance

With a second PC an extra computer can concentrate on the motor controlling without being interrupted by any multitasking. That means the motor performance will be better. Clean micro stepping is easier possible.

Better Windows multitasking

The multitasking of your Windows PC will improve while the machine is milling since two dedicated PCs can share the load.

Space for future enhancement

A second PC offers space for future enhancement, e.g. for a closed loop control. That requires an add on card and a rotary encoder for each motor and will prevent work pieces from being damaged by lost motor steps. Without a second PC it would be very difficult (= expensive) to provide such a solution with a single Windows PC.
Use a cheap IO card instead of the printer port and you get more IO lines, a secure spindle controlling, a 8 bit output for (HF = high frequency) spindle rotation control etc.

Low cost

A second DOS PC is cheap, maybe 25 $ second hand and it will protect your expensive Windows PC or your Windows notebook from being damaged by experiments on the printer port and such.

Serves as electronic housing

The second DOS PC can be used as a nice case for your do-it-yourself motor electronic. You could put it e.g. into the 5 1/4" bay(s). Drain the +5Volt logic power from the PC's power supply and your motor power supply will be much easier to be built (a transformer, 4 diodes and a big capacitor will do it, no stabilized output needed).

Linux Port for more flexibility

In my opinion, Microsoft Windows is a questionable software, e.g. both in privacy and security matters. With XP Microsoft has gone too far. That's why I do not want to put too much effort into very OS specific programming like device driver writing for Windows. I'll rather use that time to port the CncPlayer to Linux one day.

PC/104 for smallest size

If you don't like a second big desktop PC for whatever reasons you could replace it by a single board PC of PC/104 style. These are ordinary PCs but shrinked to about only 100 mm x 100 mm in size. They require only +5Volt power. You can attach a floppy drive but they have a 2 MB silicon disk on board. So you can omit the floppy drive and run the software from the silicon disc. No memory is lost during power off . Since a PC/104 is very small you might put it into your existing electronics' or machine's case. PC/104 have graphics on board, Com Port, Printer board and all you know from a "real" PC. Yes, CPC.EXE will run on a PC/104. In fact, many commercial cnc machines have a PC/104 built in. A PC/104 is a great piece of technology but it's round about 250,- Euro, to give you a raw image.

Baby board is small and affordable

A cheaper solution than a PC/104 board would be the usage of an ordinary baby AT board or one of the newer micro ATX boards. FLEX ATX boards are even smaller. You could attach a common Compact Flash Memory Card to the board and use it as your drive, boot and run any program from it. That's really cool, small and cheap. Though, that solution is bigger in size than a PC/104 and it also requires an ordinary PC power supply (while +5 Volt will do it for a PC/104). If size and full blown power supply doesn't matter then its really a small yet affordable option. BTW, PC power supplies from web server are very small. Only 40 mm x 80 mm x 220 mm in size.

There are lots of advantages a 2nd PC offers. Give it a try.