<p data-pm-slice="1 1 []">I&rsquo;ve always wondered how vending machines can tell different coins apart so quickly. Do they check the weight, size, metal composition, or some combination of these things?

I recently started thinking about it after using an older vending machine that rejected one of my coins even though it looked perfectly normal. It made me curious about how do vending machines read coins and what happens when the machine can&rsquo;t identify one correctly.

Has anyone here worked with vending machines or knows how the coin recognition system works? I&rsquo;d be interested to hear how the technology has changed over the years.