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Try edx.org or coursea
You can find it here man... http://www.openculture.com/freeonlinecourses @lucian68
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Instrumentation, Servicing, and Automation Association has a number of online courses that are ABET accredited and will grant a certificate of completion after finishing. Most of the courses are for machine technology and general equipment operation. It may be a good idea to look into getting certificates now, although it does cost money, but not much and will be valid preceding your high school graduation. If you are employed using the certificate then it will last even longer.
Besides that, it's all about what you want to do. There are several free classes from organizations looking for potential employees. Just keep checking out meet-ups and community classes. Try to take physics, trig, and calculus in high school, and you should be golden. Self-study is a good secondary option, the best possible option is getting a group of friends with the same goals in mind that you do and going out as a group to study or take classes.
khanacademy.org is one of my favorites for free online classes and refreshers.