In this blog post, we’ll explore the scientific principles that vending machines—which we use frequently in our daily lives—use to accurately determine a coin’s authenticity and face value.
Coins are a very common sight in everyday life. Although their sizes vary slightly depending on the type, people usually identify a coin’s value by looking at the number on its face. However, the visible number alone is not enough to determine whether a coin is genuine or counterfeit. This is where vending machines step in, acting much like gemologists to authenticate coins. They meticulously examine the coin’s characteristics to determine its authenticity and accurately identify its denomination. Let’s explore the scientific principles behind how vending machines can distinguish coins that are difficult for the human eye to tell apart.
When a coin enters the vending machine through the coin slot, it passes through a device called the “coin mechanism.” Here, the coin undergoes two main processes for authentication. The first is determining whether the coin is genuine or counterfeit, and the second is identifying its denomination. At first glance, these two processes may seem simple, but they are based on scientific principles that utilize electrical and optical properties.
The interior of the coin mechanism consists of several stages for coin authentication. The first process takes place at the very top, the second in the middle, and the bottom section serves as a passageway for the authenticated coins.
First, let’s take a closer look at the first process. When a coin enters the first identification zone, a device inside the CoinMek measures the coin’s electrical properties, and the identification unit analyzes the results. Every material has its own unique electrical conductivity. Electrical conductivity is a physical quantity that indicates how well an electric current flows through a material. The higher the electrical conductivity of a material, the better it conducts electricity. You can think of this as a similar principle to how, in the animated series ‘Pokémon’, the protagonist Pikachu’s electric attacks are effective against the Water-type Squirtle but have little effect on the Rock-type Longstone. Of course, actual coin authentication in vending machines is carried out through measurements far more precise than this analogy suggests. Meanwhile, coins of the same denomination are manufactured using specific metal materials and specifications, giving them unique electrical properties. For example, South Korea’s current 500-won and 100-won coins are made of brass (75% copper, 25% nickel), while the 50-won coin is made of an alloy consisting of 70% copper, 18% zinc, and 12% nickel. Since the composition and proportions of the metals used in each coin are fixed, it is not easy to counterfeit a coin with the exact same electrical properties as the genuine article. Therefore, when CoinMek measures a coin’s electrical properties and detects values that deviate from the standard for that coin, it can be identified as a counterfeit. In this way, the vending machine quickly and accurately detects counterfeit coins that are difficult for the human eye to distinguish, and filters out coins that do not meet the standards through its internal return or ejection mechanism.
Since both the 100-won and 500-won coins are made of brass—75% copper and 25% nickel—and have similar electrical properties, it is difficult to completely distinguish between them based on the first step alone. Therefore, these coins undergo a second step for more accurate detection. In this second step, light-sensitive sensors play a crucial role. Coins that pass the criteria in the first stage pass between two plates located in the second identification zone. One plate emits light toward the opposite plate, while the other is equipped with a light sensor that detects the light. When a coin passes between the two plates, it blocks the light, causing the sensor to be unable to detect the light for a certain period of time. By measuring the duration during which the coin blocks the light, the coin’s size can be determined. All coins vary slightly in size. Among the coins currently in circulation, the 500-won coin has a diameter of 26.50 mm, the 100-won coin is 24.00 mm, the 50-won coin is 21.60 mm, and the 10-won coin is even smaller at 18.00 mm. Therefore, generally speaking, the diameters of the coins decrease in the order of 500 won, 100 won, 50 won, and 10 won. Since the coins pass between the two plates of this device at a constant speed, the larger the coin’s diameter, the longer it takes to pass a given point. To make this easier to understand, let’s imagine a railroad track with a traffic light on the other side. Imagine a train and a car passing through the railroad tracks while we’re watching the traffic light on the other side. When a train passes through the tracks, the traffic light remains out of sight for a longer period than when a car passes. If we think of the traffic light as a sensor, the train as a large coin, and the car as a small coin, the machine determines the coin’s size by measuring the time during which the traffic light—or sensor—is not visible.
Vending machines are a common sight in our daily lives, but you probably haven’t given much thought to the principles behind how they detect coins. While the principle may seem simple at first glance, it actually involves technology that precisely measures a coin’s electrical properties and size. If you’re wondering whether a coin you have is counterfeit, inserting it into a vending machine is one way to find out. This is because vending machines quickly analyze the characteristics of coins—which are difficult for us to verify with the naked eye—to determine their authenticity and face value.
