PLC with VB Interface

Hello, for a school project I am planning on doing some sort of "home automation" project where I can control lights, locks, etc. from a Visual Basic form through a PLC.

I have a little experience programming PLCs, and have experience using Visual Basic, but not together.

What is the easiest way to get them to communicate? serially? What do I need? I have a Allen-Bradley Micrologix 1000 PLC, but I can most likely get any type if I need to.

I really don't know much about PLCs except how to program them. Any help would be greatly appreciated.

Thanks.
Paul

If you have RSLinx and you know how to program a DDE/OPC link it is very easy. If don´t have RSLinx you will need some libraries to make the comunication.

There are various versions of RSLinx, not all will allow DDE/OPC communications. Check the Rockwell Software website for more details. If you register on the site, I'm sure you will find examples of connecting VB to a PLC in their knowledgebase.

Why use a PLC in the first place??

Hi there,

I have done something similar to you a couple of years back when I was in my second year of engineering. If you are planning to use visual basic as your GUI (Graphical User Interface) screen, then the equipment control information has to be passed on from either the Computers Serial or Parallel port. I do not know how many appliances you wish to control, but keep in mind that the computer's parallel port has around 14 pins that can be used as I/O's!! If you have less than 14 appliances, I would use a 5V relay at each individual pin and use it to control an appliance. This way you would completely eliminate the need to spend additional money on purchasing a PLC and the bigger headache of learning how to program it.

If you do need to use a PLC for your project, I would suggest you use parallel communication with an encoder type setup from your PC side. One thing you have to keep in mind is that the Voltage output form the parallel port is 5 Volts, whereas most of the PLC's DC inputs are 24 Volts. So you would need a transistor and an additional power suply. By an encoder type setup I mean say for example you have 8 applices you wish to control, connect PLC I/O 1 to Output 1 of the parallel port, PLC I/O 2 to Output 2 of the parallel port and PLC I/O 3 to Output 3 of the parallel port. Now define the following bit sequence:

000- Appliance 1
001- Appliance 2
so on....
111 - Appliance 8

so you need just 3 bits to control 8 appliances. Ladder logic in this case is nothing but just mapping the contacts for each input to a relay output and hence, my subject.....Why use a PLC in the first place??

Connect the 8 relay ouptuts of the PLC you wish to a relay each for each appliance and you are done.