Visual Basics to PLC

Yes, it is possible if the PLC accepts commands through Ethernet and/or serial cable, you just have to program it.

Yes, you have to talk to a Siemens sales/applications engineer to know about the communication modules between the PC and the PLC (interfaces) and the programming involved.

Ethernet is a lot faster than RS232, but you will notice this diference in data heavy transmissions, for your start - stop application the serial port might be good enough.

Of what meaning and of what consequence would <...STOP and CONTINUE function...> have to a PLC? Isn't that the same as an on/off switch?

Others are correct that you can communicate to a PLC over ethernet from a VB program. However if you want the ability to actually RUN VB (OR C+) programs within the PLC environment, and share data over the backplane, then your best PLC option is Rockwell Automation's ControlLogix platform. They have a readily available "SAM" module, that is a full blown Windows PC, that fits within a PLC slot. The module has ports for monitors, mouse, USB and keyboards. It has Wondows pre-installed, and the user has full Windows programming control options including playing "solitare" if you so desire.

I used one of these years back to allow me to write a custom ethernet interface to a coating weight gauge. Then I backplaned (not a real word) the data to/from the Logix controller-- Still in operation today. and the good thing is once set up you can disconnect all the peripherals and it looks just like a normal PLC card.

Numerous power cycles/failures since then, and I have never had to reconnect the monitor or keyboard- it just boots up and runs the VB program, that I put in the "Start=up folder"

I realize I sound like a salesman, but I am very pleased with the performance, and the only warning I have is the price may seem high depending on your application.

good luck!

I imagine you resisted the temptation to hook your finished controller to the internet using its Windows internet capability. Properly done, that would have meant running antivirus programs, continually upgrading the software and hardening the firewall, etc., to deal with today's hostile environment. Poorly or non-maintained old versions of operating systems running inside aging but-still-works-fine instruments can be a big source of vulnerability in an industrial network.

It was hardly a temptation , in fact I only resorted to this card because I could not comm directly to the gauge using the standard Logix Enet card. Seems it only allows Rockwell's protocol.

Yes, I was (am) afraid to change anything on the setup once it was all working. It is a very expensive uni-tasker!

Yes it is possible by using visual basic program .the issue is not within type of the processor . but with serial port. if S7 300 PLS has an RS232 interface you should convert it to USB(universal serial bus) by using FTD device USB to serial bus converter i think the best device number you can easy deal with, it is FTD232RL comes with its software driver installation for more details go to search FTD232RL DATASHEET .

If all you need is to turn an input on or off using VB program from a PC, then insert an opto 22 card into pc and take a in put to or from unit. Cheap way to get what you want. For no more then you want to control.