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"Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." Mark Twain
A conscientious manufacturer dictated by safety will rather buy good code or will employ a programmer to create it for him.
what you need?
You seem to intend selling your software skills. A good method might be is to use the existing equipment and find something that need improvement and take it from there.
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Never do today what you can put of until tomorrow - Student motto
The software in household appliances are actually already stored in permanent read only memory (ROM) ( I would call it firmware). The end user can only use it but cannot change it in any way.
The manufacturer of equipment cannot allow any person access to the program running the equipment because he may be held liable for injuries or damages.
Example : microwave oven
If any person were capable of entering new software into the oven and that person omitted checking the status of the door while in a cooking cycle.
Somebody opening the door (for a good and valid reason) while in a cycle would then be subjected to radiation.
No manufacturer can or will take that change with the safety of equipment.
Users are therefore limited to the functions and control supplied by the manufacturer.
The design of the software at the factory is usually subject to strict control and mostly prescribed by law. (at least common law in the absence of other law)
Each factory will have its own set of rules and designated employees would know what to do or what it is all about.
If you intend to start developing software your first consideration should be :-
Do I think I can design better, safer, cheaper software than the existing designers and are there any chance of achieving a fair market share.
You would have to start by studying
1 International safety regulations and rules.
2 Health and safety law in the countries where you intend to market.
3 The manufacturers to be involved.
You will have to build prototypes and submit it to tests and sell it to manufacturers..
Good luck.
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Never do today what you can put of until tomorrow - Student motto