starting problem

hello everyone,
first things first, THIS IS THE BEST WEBSITE for any information on PLCs. I am new in the field of PLCs and ******* systems, and this website is like heaven's answer to all my problems.
Currently I have 2 micrologix 1200 PLCs with RSLogix 500 software. I am learning the ladder logic slowly. Later (i think it will be a long time) I want to learn about creating HMI using VB. I know some VB.
Can some one help me by pointing out the intermediate goals involved? again, i am a rookie, so help me pls.
thanks to all the PLC gurus and best regards,
taknevs

taknevs said:

...I want to...creat[e] HMI using VB.....
Can some one help me by pointing out the intermediate goals involved?

Click to expand...

The goal: Get PLC information into the PC for display on the monitor.

Task breakdown:
1) Get PLC information into the PC
2) for display on the monitor.

The last task is fairly straightforward for a VB programmer. Assuming that a VB variable has the PLC information, it's a fairly simple matter of plopping objects on a form, and writing some code to alter the object's property(s) based on the value of the variable. There are libraries of all types of pre-made ActiveX objects with useful properties.

The first task is trickier (depending on the PLC). To get the data, you need some kind of driver. You can buy one, or you can write your own (assuming that the protocol is published, or you are good at trapping data packets and have an existing driver).

I can't remember if the Micorlogix uses the DF1 protocol (published), the DH-485 protocol (unpublished), or a different one.

If writing your own driver doesn't sound like fun (it isn't), then you can buy one. There are several on the market, starting with RSLinx (which you are familiar with - but you'll have to upgrade it if you want it to talk to anything other than AB software), Kepware, InGear, to name but a few.

Each come with examples of how to write VB code to interface with them.

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Or, you can save youself some time, and go with a canned HMI package, perhaps just to start with to see what they are all about, and to get ideas from them. Most offer some sort of FREE "cripple-ware" demo versions, limiting you in time (2 hours before needing to restart) or the number of tags (=~ VB variables) you can set up (or both).

Being canned products, they simplify the getting of the PLC data to the screen, exposing the properties (color, blinkingness, size, position, etc.) and tying it directly to the tag. The tag database is also set up to make it easier to reference the PLC data tables and the frequency that the data needs to be refreshed.

Just my opinion, but one of the primary reasons I switched several years ago to PLCs from high level langauge and single board computers was the increased availability of reasonably priced, readily configured operator interfaces and HMI software geared to PLCs. It is, in my opinion, going to be hard to justify the time required to write, debug, and maintain your own communications drivers and high level programming for operator interface. Unless you have a very high volume or your time is free the economics just don't work out for "rolling your own".