Vending machines that accept banknotes have a paper money recognition mechanism and a paper money transmission mechanism \[[1](https://patents.google.com/patent/US5485907A/en)\]. These machines use sensors to recognize banknotes based on multiple observations of different characteristics, such as the size, shape, color, and pattern on the banknote \[[2](https://www.wonderopolis.org/wonder/how-smart-are-vending-machines/)\]. When a banknote is inserted into the machine, the front sensor of the paper money recognition circuit is triggered to send a signal to a step motor, which drives the transmission unit, carrying the inserted banknote through the upper mainframe and the recognition circuit \[[1](https://patents.google.com/patent/US5485907A/en)\]. The recognition circuit analyzes the characteristics of the banknote to determine its value and authenticity \[[3](https://vending-machines.ie/how-do-vending-machines-know-money-is-real/)\]. Modern vending machines are highly capable of distinguishing between genuine and counterfeit banknotes using various methods, such as ultraviolet and magnetic sensors, infrared sensors, and watermark detection \[[3](https://vending-machines.ie/how-do-vending-machines-know-money-is-real/)\]. Once the value and authenticity of the banknote have been determined, the vending machine calculates the appropriate amount of credit and dispenses the product or service requested \[[2](https://www.wonderopolis.org/wonder/how-smart-are-vending-machines/)\].