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Sethiroth

New to PLC. Questions about a project.

14 posts in this topic

Hello, I am a PC tech/ Database programmer. I have almost no experience with PLC's. I have a question. I am working on a project where I would like to have say 24 different contact buttons. I want each button to have a "value". Everytime a button makes a connection, I want it to add its "value" to a "total" field. The "total" field will start out at Zero. So if contact button #8 makes a connection, it adds its value (we'll say its value is 200) to the "total" field (0). So it should do this. Total = Total + Value. And then I want another button to reset the "Total" value. And I want a display of some sort to display the value for "Total" at all times. How hard would this be to do, and what would I need? Would a PLC board be the way to go? Or would some other way work better/Cheaper? And what is available for a display? The "Value" field shouldn't ever go higher then six characters.

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That would be extremely easy to do with a PLC, but it seems to be a little too simple. What are you doing with the value you are creating? Would you be open to using a touchscreen HMI for the buttons, or are you set on hard-wired controls? What is the main control of the machine?

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Well, the touch screen idea is a great idea, but the contacts need to be physical contact switch's, so it won't work in my situation. Im looking to do about 24 input and maybe 12 output. I would want four displays. The displays needs to be seperate from the PLC board. One of the contact buttons will switch focus from one display to the next. So. Display1 focus = yes Display2 focus = No Display3 focus = No Display4 focus = No When contact button "SwitchFocus" is made, Display1 focus = No Display2 focus = yes Display3 focus = No Display4 focus = No When contact button "SwitchFocus" is made again, Display1 focus = No Display2 focus = No Display3 focus = Yes Display4 focus = No Ect... This is for a game I am working on. I don't really have any controls in mind other then the contact buttons. The displays are for "scores". Im wondering how much a PLC board this size would cost, or if there might be a cheaper alternative. Thanks!

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I wonder if a PC running a small VB app driving a discrete I/O module, might be the most cost-effective solution.

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A PLC would run you a couple hundred dollars, and is kind of clunky if you want the system to be small. Perhaps an embedded controller? For displays you could check out something like Noritake.

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I am not framiler with embedded controller's. I will look into those. Are they easy to program? The other reason I was looking at PLC was ease of programming. I am not concered with size. The housing of the project will be quite large. Also, those Noritake displays look nice! I will look into those. Thanks for showing them to me! Edited by Sethiroth

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If reliability is the main consideration, you're right to consider a PLC over a PC-based solution. Here's something else to consider.. Will you be able to program this with your employer's software, or will you have to buy your own? PLC software varies in price from several hundred to several thousand dollars. If you're only planning on making one (or a few) of these devices, you're probably going to want to limit your choices to the PLC families that use the least expensive software, or better yet ones that can be programmed with software you already have access to.

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I will be able to use the software available from work. Atleast at first. But I may eventually have to buy my own licenses. Which families have the lowest priced software? Do you use the same software for Embedded controllers as you do with PLC's? These look to be alittle cheaper, but im not sure how the work per say. Does anyone know of any good reasorces for learning about these?

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I've never used them, but this might be your best option: http://www.entertron.com/controllers.htm The software is free, and the PLC's are reasonable. This might be even better, has a small led screen built in: http://www.lt-automation.com/T100(e).htm Not sure about the software cost. Ken

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Sounds like you do want to stick with a PLC. What I am referring to as an embedded controller is just a processor on a board, like the kit I learned to program in college. PLC will be reliable and much easier to program. We carry Mitsubishi, and their best deal for a simple controller is the Alpha programmable relay. Controller is around $200, programming cable around $100 and software around $100. If you know how to use the PLC boards at work, you may want to stick with those due to familiarity though.

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I checked these out. The 24 input/output controller is only $200? What is the going price for something like this? Or do you normally peice together multiple boards to achieve the desired amount of I/O's?

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No, the 24 I/O unit is a bit more. I'll PM you with more detail.

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Embedded PC's are just as easy to program as regular PC's. There are some very low end ones such as the "Rabbit PC's" and "Basic Stamps". These machines are specifically targetted at being extremely easy to program for hardware guys, but they tend to be a little limited in terms of power. You can go all the way from those up to full blown PC's. Check out "Nano ITX" motherboards. These are full blown PC's that have been carefully designed to use extremely small form factors...small enough to fit in a car. With almost any of these products, they come with a huge tool kit of software and libraries to help you do development. Sometimes there is a "production" version and a "developer's kit". For your first one, obviously you want the developers kit. Many electronics houses such as www.mouser.com sell several different varieties and you can find many more on the internet. As to the switch button problem...if you look around and google for keypads and such, there are a number of "keyboard interface" boxes. These come as a circuit board that has places for switch contacts on it that outputs key strokes to either a USB or PS/2 port. You can simply wire up your choice of buttons to it and from the PC point of view, it's just seeing an ordinary keyboard. Check out www.xkeys.com for an example of this direction. Finally if you want to look for a very cheap PLC and you want to go with a major brand name, the Allen Bradley Micrologix series is pretty good. You can get free software to program some of the lower end models. Another source is www.automationdirect.com. The quality from those guys is often variable but check out the reviews for their DL series PLC's on this web site. The key difference between the two is that PLC's usually (but not always) tend to go for reliability. The software interface is specifically directed towards electricians more than programmers. On the other hand, embedded PC's are targetting the "embedded" market...in other words, when you are building a gadget such as a DVR or a networked hard drive where you need the power of a PC to fit in a small space and work very reliably. They cater specifically to hardware hackers who are usually very versed in more traditional programming. Since you seem to suggest that you want the reliability of the PLC but you don't know much about them, I'd suggest you consider going towards embedded PC's. This gives you the reliability of a PLC but the familiarity of the programming interface. If you step all the way out on the limb with PLC's, then expect to pay a bit more because it's sort of like the difference between modular and integrated stereo equipment. You will pay an extra premium for the development environment and the extreme modularity of the PLC approach.

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I've read thru all the posts and I'll lend my two cents. Years ago I would ahve done what you describe with an 8048 chip and a Printed Circuit Board that I soldered together myself. These programmed in machine code and required little in terms of investment. I even built a calculator using one. The PLC approach is going to give you "bullet proof" execution, but will cost for the hardware and learning curve time. The embedded PC that paul touts might be the best fit given you know VB and can leverage your PC progamming skills. I'd definityle look at a linux or BSD operating system and use C++ if it were me.

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