Law is complicated, and I can only offer my layman perspective on United States patent law.
In general, patents are a particularly powerful area of law, because independent invention is not a defense against patent infringement1. Even if you've never seen or heard of a particular patent before, you can violate it if you implement the patented system or method. This is different from copyright, where never having seen the original material is a valid defense against infringement. In other words, the law makes it incumbent upon system developers to ensure that they do not violate any existing patents. This can be very difficult to do, and for this reason there are lawyers who specialize in searching for existing patents.
Since hobbyists likely cannot afford to do a patent search, doing system development will necessarily be legally risky, especially in an area densely populated with patents. This is a property of how patent law operates, and cannot be avoided without overhauling at least some parts of patent law. (The allowance of "independent invention" as a full defense under the law would be a great start.)
One limited solution software licenses have employed is to include patent retaliation clauses: if a plaintiff sues the maker of a freely-licensed system for a patent violation, then the system owners automatically rescind the plaintiff's right to use parts of the defendant's system under other patents. In other words, "If I can't use your patents, then you can't use any of mine." This is obviously a limited solution; it only has value if the defendant has any important freely-licensed patents.
1. Note that by demonstrating your infringement of a patent was not willful, you may minimize your punishment down to paying merely a reasonable licensing fee for your past use of the patent, instead of much higher punitive damages. Still, the licensing costs to the infringer may be substantial.