If you're building an arcade cabinet, a home arcade machine, or any coin-operated system , sooner or later you'll come across the famous pulse coin machine board and pulse coin selectors. These are small modules that translate "physical coins" into "credits" using electrical signals that are very simple to understand... once someone explains them to you properly.
Although at first glance they may seem like a tangle of wires, connectors, and DIP switches, their logic is quite clear: a coin is inserted, one or more pulses are generated, and these pulses are converted into credits for the JAMMA board, an IPAC, an Arduino, or whatever system you're using. In this article, we'll take a close look at how these boards work, what each pin does, how they relate to an HX-916-type selector, and how to integrate them with an Arduino or a PC, without leaving out any important details.
What is a pulse coin machine board and what is it used for?
The coin machine pulse board is a small intermediate circuit placed between the coin mechanisms (mechanical or electronic) and the machine's main board (JAMMA board, IPAC interface, microcontroller, etc.). Its main function is to transform the value of each coin into a number of pulses equivalent to credits.
In many classic arcade cabinets, this board was used in conjunction with mechanical coin mechanisms and physical coin counters . When a coin fell in and activated the coin mechanism's switch, the board received that input pulse, processed it according to its DIP switch configuration, and generated:
- A pulse train towards the COIN1 input of the JAMMA board (or the IPAC).
- Counting pulses towards one or two electromechanical coin counters.
Thus, depending on the coin and the configuration, a single coin could be equivalent to 1, 3, 5 or more pulses , and therefore to several credits, while the counters faithfully recorded how many coins had entered each wallet.
This logic is not only used in arcades; the same philosophy of “coin → pulses → credits” is used in vending machines, jukeboxes, public telephones and all kinds of pay-per-use systems where pulse control is simpler and more robust than directly handling digital money.
Main components of the credit card
It usually includes several elements that are easily recognizable at a glance:
On one side are the blue DIP switches , which are small microswitches arranged in a row. Their purpose is to configure the currency-to-credit conversion. Depending on the combination, it determines how many credit pulses will be generated for each pulse received from the coin acceptors, or what value each coin input has.
In addition, the board incorporates a multipin connector (in this case, with 9 pins numbered 1 to 9 from the bottom, with pin 1 being the closest to the red LED). All signals are routed through this connector: power, pulses to JAMMA/IPAC, coin inputs, and outputs to the counters.
It also usually has a status LED (usually red) that helps to check if the board is powered or generating pulses, in addition to some discrete components (resistors, transistors, optocouplers, etc.) that handle signal conditioning and isolation.
Although sometimes sold as "black boxes" without documentation, their internal design is quite logical and, with some patience, the continuity of the cables can be traced from the coin switches and counters to the main connector, as has been done in some home projects for restoring and preparing arcade cabinets.
Pin assignment and functions on the pulse coin machine board
In the specific case described, the board has 9 pins on its main connector . Starting from the bottom (pin 1, the one closest to the red LED) and moving upwards, the typical pinout is as follows:
Pin 1 – GND (common, ground): ground reference for the entire board. The grounds of the power supply, coin mechanisms, counters, and the JAMMA or IPAC board are connected here. It is the common point at which all voltages are measured.
Pin 2 – +12 V: Main power supply for the board and, in many cases, the voltage also used to power mechanical or electronic coin mechanisms and electromechanical counters. It is essential that this line is stable and comes from a suitable 12 V DC source.
Pin 3 – Variable pulse output to COIN1: This is the credit output line to the game board. Here, the board emits one or more pulses for each valid coin, depending on the DIP switch configuration. It is typically connected to the COIN1 input on the JAMMA board or the equivalent input on an IPAC.
Pin 4 – (no defined use in the described case): In some variants, it may be reserved for another function (for example, a second credit output or service signal), but in the reconstructed practical documentation, it appears without a clear function. It is advisable to consult schematics or a specific service manual if available.
Pin 5 – +5 V: This voltage is used for the board's internal logic, microcontrollers, comparators, and part of the digital circuitry. Many boards operate with a dual voltage rail (+12 V for actuators and +5 V for logic).
Pin 6 – Pulse output to coin counter 1: Each time the board registers a coin corresponding to coin acceptor 1, it emits an electrical pulse on this pin, incrementing the associated mechanical or electronic counter. In this way, the counter reflects the number of actual coins accepted by that channel.
Pin 7 – Pulse output to coin counter 2: This works the same as the previous pin, but for the second coin acceptor. It allows for independent tracking of the coins entering each slot or coin type.
Pin 8 – Coin Pulse Input on Coin Mechanism 1: This is where the pulse output or switch of the first coin mechanism is connected. When a coin is inserted, the mechanism momentarily closes the circuit and sends a pulse to this pin, which the board translates into credits and counting pulses.
Pin 9 – Coin Pulse Input in Coin Box 2: equivalent to the previous one, but associated with the second coin box. It allows working with two different coin channels (for example, two different values or two physical slots).
With this structure, each time a coin activates the switch in its coin acceptor , the circuit does three things almost simultaneously: it processes the coin according to its programming, generates credit pulses to COIN1, and updates the corresponding coin counter.
Relationship with COIN1, COIN2 and service button on JAMMA boards
A very interesting detail of these classic installations is how the COIN1 and COIN2 inputs of the JAMMA board are used . In the configuration described, the output of the coin machine board goes only to COIN1, while COIN2 is reserved for the service button.
In practice, this means that the pulse signal generated by the board on pin 3 (output to COIN1) corresponds to the actual coins, i.e., what the player pays. Each burst of pulses represents a number of credits and is also reflected in the coin counters via pins 6 and 7.
COIN2 , on the other hand, is used as a "service credit" input . The service button, connected to this line, adds credits to the game board without affecting the coin counters or the total revenue. This way, if a coin gets stuck or a customer claims a credit that hasn't been credited, the operator can compensate using the service button without altering the coin count.
This solution is especially practical because it prevents discrepancies between the amount collected and the games played . By not mixing service credits with physical coins in the counters, the machine operator can check the cash register with confidence, knowing that the counters only reflect the actual coin entries.
In many modern arcade projects, where an IPAC and a PC with emulators are used, this logic is exactly replicated : COIN1 comes from the output of the credit board or the coin selector, while COIN2 is reserved for an internal button for testing or service, without linking that button to any collection system.
HX-916 Coin Selector: How it Works and What It Offers
Beyond the classic coin acceptor board, it's very common nowadays to use an electronic coin selector like the HX-916 model , which integrates much of the logic needed to validate coins and generate pulses. These types of devices are used in both DIY projects and modern commercial machines.
The HX-916 can recognize up to 6 programmable coin types . This means you can teach it, for example, 6 different coins (different denominations or coins from different countries), and the coin selector will learn their physical characteristics to distinguish them. When the selector receives a coin, it analyzes:
- Diameter of the currency.
- Weight of the metal.
- Fall speed during the internal tour.
Using these variables and an internal statistical algorithm , the device determines whether the coin is valid and which pre-programmed type it corresponds to. Furthermore, it allows the selection of different levels of accuracy, making the system more or less demanding when accepting coins.
Once a valid coin is identified, the HX-916 generates a sequence of pulses at its output . The duration of each pulse is configurable between approximately 30 and 100 ms, and the number of pulses depends on the coin type: for example, a 1-unit coin might generate 1 pulse, a 2-unit coin 2 pulses, and so on.
With its pulse output, this selector fits perfectly with credit boards, microcontrollers, or JAMMA/IPAC boards , since all these systems are based precisely on counting pulses to determine the assigned credits.
Technical specifications of the HX-916 selector
From an assembly point of view, the HX-916 behaves as a fairly simple module to integrate, with technical specifications designed for intensive use in arcade machines, vending machines and the like:
- Model: HX-916.
- Supply voltage: 12V DC.
- Standby current: approximately 20 mA.
- Working current: around 350 mA in operation.
- Coin diameter: supported range from 15 mm to 29 mm.
- Coin thickness: approximately between 1,8 mm and 2,8 mm.
- Number of programmable coin types: up to 6.
- Output signal type: pulse signal.
- Identification success rate: about 95%.
- Maximum identification time: less than 0,6 seconds.
- Working humidity: below 95%.
- Body Material: plastic.
- Approximate dimensions:
- Weight:
- Includes:
Thanks to these features, it is very suitable for vending machines, arcade games, jukeboxes, and public telephones . In all these cases, the pulse output allows for very direct integration with the rest of the control electronics.
How to integrate a pulse coin selector with Arduino
If your goal is to connect a coin acceptor to a Arduino (for example, an Elegoo UNO R3 or a Arduino UNO original) And, through it, communicate with a PC or a MAME-type emulator; the good news is that the programming part is much simpler than the electrical part.
The basic idea is to take advantage of the Arduino hardware interrupts to detect the pulses coming from the coin selector. In the Arduino UNO / Elegoo UNO, the pins with hardware interrupt are 2 and 3. The interrupt is configured in the block setup () of the sketch so that it fires on the rising edge of each pulse.
In this way, each time the selector sends a pulse when a valid coin is inserted, the interrupt increments a counter , and your program can determine how many pulses have arrived and which coin they correspond to. Furthermore, by using interrupts, the microcontroller doesn't have to constantly monitor the pin, saving resources and preventing lost pulses.
There are pre-made scripts, such as the example available in public repositories (for example, hxlnt/arduino-coin-acceptor ), that show how to read and process these pulses. From there, you can modify the code so that, when a certain number of credits is reached, the Arduino sends a specific action to the PC, such as simulating pressing the number "5" to insert coins into MAME.
Physical connection: power supply and pulse cable to Arduino
On the hardware side, a novice user usually wonders mainly where to connect the pulse wire and how to power the coin acceptor . A typical diagram might look like this:
On one hand, the coin acceptor (such as the HX-916 or a similar model) is powered by 12V DC . It is perfectly possible to use a 12V LED strip power supply, provided it provides the necessary current (approximately 350mA operating current plus a safety margin). These adapters usually come with two output wires (positive and negative) that connect to the 2-pin power connector of the acceptor (respecting the polarity).
This 2-pin connector, found on many acceptors, corresponds to a 12V electromagnetic valve or solenoid , responsible for blocking or allowing the passage of the coin. Applying 12V releases the mechanism, allowing the coin to be inserted and validated. While the selector is active and powered, this valve operates in coordination with the internal recognition system.
On the other hand, the acceptor's pulse output is connected to a digital pin on the Arduino. Ideally, a pin with an interrupt (2 or 3) should be used, and the sketch should be configured to detect pulses on that pin. It is also essential to connect the acceptor's ground (12V GND) to the Arduino's ground (5V GND) so that both share the same electrical reference.
The exact point on the board where the pulse wire connects is usually labeled COIN, OUT, SIG, or something similar on the acceptor. From there, the included cable connects to the Arduino pin defined in the code. It's advisable to check the manufacturer's datasheet or PDF (for example, "letpos pro" PDF documents) to confirm the exact assignment of each wire.
Using Arduino as a bridge to a PC or emulator
Once the Arduino is receiving and counting coin pulses, you can use it as an interface between the coin acceptor and the PC . The most direct way is to connect the board to the computer via USB and have the Arduino send data through the serial port, which can then be interpreted by software on the PC.
However, if you're looking for something more transparent to the system, many hobbyists modify the code so that the Arduino simulates keystrokes when a certain number of credits is reached. For example, you can program it so that, after receiving a pulse or a series of pulses equivalent to a coin, the microcontroller sends the signal of the "5" key on the numeric keypad to the PC, which in MAME is usually the coin insertion key.
From the end user's perspective, this means that each coin inserted into the acceptor triggers a virtual "coin" in the emulator , without requiring any changes to the PC's settings. In terms of wiring, you only need the USB cable between the Arduino and the PC, plus the power supply for the acceptor and the pulse wire.
Some Arduino-compatible board models (such as the Elegoo UNO based on ATmega328P with ATMEGA16U2 for USB) are very practical in this respect, since they behave to the operating system as a standard serial port or, with certain modifications, even as an HID device capable of emulating a keyboard.
Manufacturer warranties, quality, and documentation
When purchasing a pulse coin machine board or coin selector, especially for commercial use, it's important to check the warranties and terms offered by the manufacturer or supplier . Many reputable manufacturers offer:
A quality control team is responsible for inspecting all products before shipment, ensuring that each unit meets established standards. This reduces the risk of coin validation failures or electrical problems.
Commitments to controlled delivery times , usually negotiated with the customer or set in short periods (for example, shipments within 7 days of receiving payment). This is especially relevant if you need to replace a downtime machine that is generating revenue.
In addition to competitive pricing, many suppliers focus on offering good value for money , including OEM and ODM options. This means they can manufacture custom modules to your specifications, maintaining the same quality standards and strict batch control for large quantities.
Another key point is after-sales service and logistics . Some manufacturers guarantee ongoing support after the sale and offer professional worldwide shipping, which is useful if you assemble machines for different countries or manage geographically dispersed amusement parks.
Regarding documentation, it's common to find PDF manuals (like those available through links such as Letpos Pro in Spanish) that detail connections, pin assignments, coin programming procedures, and adjustment parameters. Having this manual on hand greatly simplifies setup, especially for understanding the function of each DIP switch or connector without having to rely solely on a multimeter.
Both the credit board and the pulse coin selectors form a fairly coherent ecosystem: the physical coin is converted into simple electrical signals that any game board, microcontroller, or PC can understand . By understanding what each pin does, how the pulses are generated, and how to configure them, it's possible to build anything from a very basic home arcade machine to complex payment systems with various coin types, independent counters, and service buttons to handle issues without affecting the total revenue.