How it Works

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Coin acceptors, also known as coin mechs or validators, are used across the self service industry, providing a safe and secure cash acceptance system. But what do they actually do and how do they work? An electronic coin acceptor validates a coin based on physical properties such as diameter, thickness and magnetic content and then sends a corresponding signal to its output connector. It doesn’t give change; that is the function of a coin changer.
 
Step One
 
Firstly, coins are inserted by a customer, which traditionally was done one coin at a time. On some systems, particularly ticket machines, coins cannot be entered until the machine operates a cover opening the slot. It’s now becoming increasingly common on self check out machines in supermarkets to insert coins in bulk, a handful at a time. If the machine is not ready then the coins will be returned immediately without entering the validation sensors and can then be re-entered.
 
Once entered, the coins take a number of different routes depending on the type of coin mech. Some coins enter the validation area immediately, this is usual for front plate mounted coin mechs which are mounted directly behind the coin slot. Otherwise the coins will roll or slide down a chute into the coin mech entry. For security against possible manipulation, it is normally recommended to mount the coin mech inside the machine and to have a chute arrangement for coin entry and coin return. This makes it difficult for anyone to access the coin mech itself. For bulk coin entry coin mechs the coins will get transported mechanically to the validation sensors.
 
Sense and Sensorbility
 
Whichever route the coin follows, it will pass a series of sensors. The most common of these sensors are Optical or Inductive. Optical sensors use a series of light beams to measure coin size. With Inductive sensors, the coin passes between a pair of coils; one coil that transmits a magnetic field and the other that receives a magnetic field. As the coin rolls by, it alters the magnetic field and the variation is interpreted by the acceptor’s computer algorithm. Differences in size, shape, or metal content produce different, very precise electronic signatures that determine type and denomination.
 
These sensors validate each coin by measuring its thickness, diameter and material. Some also measure the embossing features of the coin itself. Thickness is determined by how much of the signal from one coil is received by a second coil on the other side of the coin. Diameter is measured by the change in signal on a coil when a coin passes it. Material is identified by the change in signal on a coil caused by reflections from the coin.
 
Different frequencies of oscillating fields are used depending on the measurements being taken. For example, some signals will go through the coin and some will bounce off. Different features can be measured using a small number of sensors, e.g. using six coils could measure 24 different things and also, by using mathematical algorithms, measure their relationship to each other. This is similar to the way the human body works. Think of eyes – they can see colour, pattern, thickness, and diameter while fingers can also feel thickness, diameter, shape, and the grooves on the edge of a coin.
 
These measurements are all made very quickly, which is necessary in the demanding environments in which coin mechs are used. Validators in a vending machine can process one coin per second. In gaming machines this rises to over 10 coins a second.
 
Decision Time After passing all the sensors, a decision is made to accept or reject the coin. As the coin passed the sensors, the readings were compared with pre programmed parameters held in the coin mech memory. Let’s say you inserted a one pence UK coin and the first sensor measured the material - the mech would compare the first measurement with stored parameters and it would determine the coin could only be a 1p or a 2p, as no other coin would match that particular reading. Consequently the next sensor would only need to be checked for 1p or 2p matches and the mech will recognise this. If the coin is not valid, the machine has not ‘enabled acceptance’, or has inhibited that particular value of coin, it is routed back to the reject cup. If on the other hand the coin is valid, the ‘accept’ gate will open, operated by a solenoid which is signalled to do so by the coin mech software. The coin will then pass a sensor or a number of sensors which are either optical or inductive. Only after passing these sensors will a credit message be sent to the machine, or in the case of a vending machine, to the electronic control board inside the change giver.
 
Messages used to be passed by a single pulse down individual wires for each coin. Nowadays they are more likely to be sent down a serial interface - much the same way as a PC will send a message to a printer that is plugged into it. The serial interface is normally a 2-way interface and is used by the machine to enable acceptance, inhibit acceptance, and download new coin data to the coin mech (for example the new 5p and 10p data for the coins being issued in January next year).
 
Once the coin has passed through the coin acceptor, it will either be routed directly into a cashbox or onwards to a coin separator, depending on the system. Applications that do not give change direct coins directly to a cashbox. In the case of a vending machine changegiver, coins are routed from the coin separator to coin change tubes. If one of these tubes is full, the coin is redirected to the cashbox. In the case of gaming and ticket machines, coins are routed from the coin separator to coin payout hoppers.