An Automatic Coin Sorting and Counting Machine
With the help of an Arduino Uno and several infrared sensors, this coin machine can count and sort up to 280 coins per minute.
As long as there has been physical currency, there has also been a need for ways to quickly and accurately count it. The advent of coin machines at banks and other establishments has allowed people to deposit many in a single visit and then receive a virtual credit or cash. However, this approach means the user must often pay a fee and has to give up their collection. As an efficient alternative, the YouTuber known as Fraens built his own drum-based solution which drops coins into predetermined buckets while simultaneously counting them.
The most important aspect of the design centered around the sorting mechanism since it had to be both fast and minimize the chances of falsely counting coin totals. Due to these requirements, Fraens took inspiration from commercial designs and opted for a spinning drum on top that would allow coins to fall through differently sized slots. The inside is a hopper which is where the user places their coins before they fall onto a ring that is made up of holes that barely hold each one in place. By tilting the machine at an angle, coins only fall through when they reach the center line of the drum rather than below.
The upper half of the drum sits over a stationary bracket that contains several slots which get slightly larger as the coin moves clock-wise. This means the smallest denominations will drop first while the largest one must travel all the way around before it lands in its respective bucket.
Sitting in the center is a large, geared DC motor which spins the drum on top thanks to its L298N H-bridge driver. This component, in turn, is controlled by an Arduino Uno that only runs the motor when the switch is activated.
Adding some intelligence
With the motor spinning the drum and coins falling into the correct bin, Fraens's next goal was to add a way to automatically count how many of each coin was present. Above each bin is an infrared emitter/detector pair that measures how much light is returned, and if this value changes due to a coin falling close to the sensor, then the Arduino can pick it up and increment the count. All of this information is helpfully displayed on a small LCD screen at the front of the unit.
After verifying the system worked as intended, Fraens ran a throughput test by continuously loading more coins into the central hopper and seeing how many could be sorted within a set period of time. Ultimately, he discovered that his design could handle an impressive 280 coins per minute, all while maintaining an accurate count of each denomination.