Virtual PLC ( Free software) (128 ins and outs)

[ynneb]

Here is a freeware program that simulates a PLC

http://home.scarlet.be/~dc11cd/dciplc.html

This could be good for non CNC machines or to make a auto loader, unloader for your CNC machine.

I would be interested in ideas you might have for a use for it.

[Evodyne]

Originally Posted by ynneb Here is a freeware program that simulates a PLC http://home.scarlet.be/~dc11cd/dciplc.html This could be good for non CNC machines or to make a auto loader, unloader for your CNC machine. I would be interested in ideas you might have for a use for it.

Nice freeware effort. I've made my living doing real PLCs (mostly Allen-Bradley) for years. They eventually came out with a soft PLC to run on NT. Their biggest impediment was the flakiness of Windows and the fact that it used preemptive multitasking. Kept it from being 100% deterministic. I think they may have written their own real-time kernel, but I don't remember for sure. Of course they sell their stuff to heavy industry where failure isn't an option.

One thing I would recommend if anyone is going to play with something like this and run real machinery is a hard-wired kill switch or e-stop that will remove power from the motor drives WITHOUT going through the logic. If the PC should hang you DON'T want the hardware running away.

His page has plans for the I/O board shown. I wonder if he supports other I/O boards, like the OPTO 22 stuff?

Evodyne

[gar]

050731-2104 EST USA

I agree with Evodyne. Your number one concern should be safety.

I would not consider a PC under DOS for a safety related application, and Windows is far worse.

The PLC manufacturers in designing their products have to give considerable attention to safety.

Beyond this --- never put any part of your body in a machine with power on. This is why you use lockout procedures in industrial plants. Always use a "chop stick" instead of your hand in a powered machine. Light curtains are very good if properly wired, and tested. On certain machines where our equipment was used we helped the electricians design logic so that a light curtain was actively tested every machine cycle ( these cycles were typically 20 to 45 seconds ) as compared with a typical test that was only done when the machine was powered up.

A very competent electrican I knew, and probably the best electronics electrican at a major automotive plant, did not follow the chop stick rule. This plant has chop stick signs all over the plant. One day he was troubleshooting a positive transfer machine and used his hand to trip a limit switch. The result - he lost his hand.

Also note that solid state or electro-mechanical switches can fail either closed or open, and maybe in between. For example a normally open relay contact might fail closed by the contacts welding together.

.

[TinkerDJ]

Very nice page. I've been looking for something along that idea for sometime. I deal with AB plc stuff at work to have something cheap and easy to use will be a nice project.

[Al_The_Man]

I would question wether it is even worth it, keeping in mind the full blown PLC's that can be picked up on ebay, complete with opto or relay outputs for a fraction of the original cost.
There's the hastle of waiting for Windows to load and by the time you have included the cost of a PC, the cost may be the same, if not more.
Admittedly you probabally could do away with the monitor and keyboard after development.
But especially if you have access to, or have the programming software then I can see no real advantage.
Al.

[HillBilly]

This software looks interesting. I like there I/O boards.

http://www.softwire.com/

Darek

[ynneb]

Another good link Hillbilly, thanks

Oh come on Al, dont spoil the fun with logic If I was to just experiment, I dont think I would go out and buy a PLC. View it as just a cheap experimental tool.

Gar and evondyne, I hear what you say about the safety issues with using a PC to control machinery, Lets face it, this whole site is dedicated to CNC, Computer Numerical Control. Yes play it safe, but also experiment a bit.

[smarbaga]

using a pc as a plc can be quite easy,
but to do it reliably may cost ya
depending on the evviroment it will be used in.
for instance, i built one for a gear and shaft heat treating oven:
1. micro pc motherboard
2. solid state hard drive
3. 10" touchscreen lcd monitor
4. printer port breakout board
5. solid state relays and opto inputs
( no mouse, no keyboard, ... more wires, more problems
i used dos 6.22 stripped down, and the thing just keeps running.( touch wood )
with the solid state hard disk it boots instantly, i had to make sure the variables and a few other handles were not written into the flash ram as it had only 100,000 read/write cycles.
.... i wonder if these usb flash drives can be made bootabld , that ss hard drive i used was $600 , 512meg
and i think the elo touch screen was $450

[ynneb]

I have started another forum dedicated to this software, just incase you were interested
http://www.routec.com.au/index.php?board=39.0