Bob,
What you are looking at doing can be done. The questions are, is it feasible and does it make sense to make something custom.
For our PLCs, there are three parts to the equation.
1. Hardware
2. Operating System or Firmware - in Assembly
3. Ladder programming software - created in C++
In doing a custom, you can bypass the third, however, it will make modifications challenging, even if you are proficient in Assembly.
In addition to the microprocessor, you will have to research and source components required for your application.
The next step will be proof of concept...bread boarding your design and writing the code to make it work.
The next step will be design of schematic and layout of circuit board. There are some on-line packages available, but they don't offer auto routers. The packaged products, will be quite costly. Cost layout software will allow you to create your own library of components, or select from their library. You can always use a company like PCB123 that provides software for design and layout, but you are unable to generate gerber files that board houses require for set up, therefore are beholdened to them as your manufacturer of your PCB. Although, your up front cost for software is next to nothing, your per board price will be higher than if you were to shop around to other board houses.
Once all that is done, you are ready to have prototypes manufactured. This is merely the raw board...no components. You will still have to manufacturer (populate and solder) the circuit board.
Then comes testing of the prototype. You will be exceptional if your prototype runs as intended the first time. Typically there are revisions, because theory and the real world don't always agree.
Costs associated with creating (designing) your own controller include:
1. Your time
2. Design Software
3. Board costs - set up charges, test fixtures.
4. Components.
5. Manufacturing equipment - solder irons, dipping pot, lead trimmer.
Manufacturing costs include Labor to manufacturer as well as time spent troubleshooting any problems. Believe it or not, not every component you get in will always work.
After all this, you are still not guaranteed that the design will work, or work the way you want it.
Time frame will depend on the amount of resources your employer is willing to commit. You can expect 6-12 months from start of design to production.
Even though your component cost is less than an off the shelf product, there are additional costs, such as labor and overhead costs for production, that many tend not to look at...focusing primarily on the component costs. The component costs are a hard cost, but the board does not assemble itself.
Previously, I had listed in general terms what would be required for design. The costs associated with designing your own board are primarily labor intensive, with various out of pocket expenses. Depending on how complicated your control board needs to be, your company may spend between $50,000 - $100,000 to develop your own board.
The questions your boss will ask are:
For that investment, what is our return?
How long will it take to recoup our investment and when will we be profitable?
Does it make sense to manufacturer our own control?
For an OEM that is making the board for their own use and only doing 100, the answer is never. It really only makes sense if your need is in the thousands. Even then it doesn't always make sense to make your own if you can find something off the shelf at a decent price.
Keep in mind that in addition to manufacturing, you will also have to provide your own support for the controller, which means you will have to train someone specifically, for service. Now, as an OEM that manufacturers a specific machine, you are now in the controller business as well.
We have identified three possible scenarios for which someone would consider our type of product:
1. a packaged PLC
2. another embedded controller
3. a custom design
This is our response to each scenario. www.entertron.com/info.htm
One stumbling block many companies will encounter by traveling the custom board route will be that they design for their application requirements only, not taking into account additional requirements. Redesigns will continue to add to the cost of being your own control manufacturer.
With all that being said, it comes down to saving a few dollars on production costs, while investing thousands of dollars in engineering that you will never recover vs. spending a few dollars more on an off the shelf product manufactured by another company, and without all the headaches associated with manufacturing (especially if it isn't your primary business). Keep in mind the headaches will also depend on the company you choose to work with...lol.
Why reinvent the wheel if it already exists and is affordable?
I would have to say that the greatest drawback to designing your own board is lack of flexibility. Off the shelf products are designed in such a way, that they can address a multitude of application requirements. You can always find a standard product that will have additional analog or digital capabilities. Unless you design it in to your board, you will be stuck if a customer comes to you and says I want to be 100 of your machines in the next month with this feature. If you don't have the feature in your board, you will not be able to meet your customer's goal.
We have talked with countless companies that went the design your own controller route, only to regret it later on.
Hope this provides you with some additional perspective.
God Bless,
