If you're building a arcade cabinet, a home arcade machine, or any coin-operated payment systemSooner or later you're going to run into the famous coin machine pulse plate and with pulse-based 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 cables, connectors and dip switches, their logic is quite clear: A coin enters, one or more pulses are generated, and those 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 step-by-step look at how these boards work, what each pin does, how they relate to an HX-916-type selector switch, 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 pulse coin machine board is a small intermediate circuit It is 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 that are equivalent to credits.
In many classic arcade cabinets, this board was used in conjunction with mechanical coin acceptors and physical coin countersWhen the coin fell and activated the coin mechanism's switch, the board received that input pulse, processed it according to the configuration of its dip switches, 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 currency and the configuration, a single coin could be worth 1, 3, 5 or more pulsesand therefore to several credits, while the accountants faithfully recorded how many coins had entered each purse.
This logic is not only used in arcades; the same philosophy of “currency → pulses → credits” It 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 easily recognizable elements at first glance:
On one side are the blue dip switchesThese 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 plate incorporates a multipin connector (In this case, with 9 pins numbered from 1 to 9 starting from the bottom, with 1 being the closest to the red LED). All signals enter and exit through this connector: power, pulses to JAMMA/IPAC, coin inputs, and outputs to the counters.
It also usually includes a status LED (usually red) which helps to check if the board is powered or if it is generating pulses, in addition to some discrete components (resistors, transistors, optocouplers, etc.) that are responsible for signal conditioning and isolation.
Although they are sometimes sold as “black boxes” without documentation, Its internal design is quite logical And, with some patience, you can follow the continuity of the cables from the coin switches and counters to the main connector, just 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 plate has 9 pins on its main connectorStarting from the bottom (pin 1, the one closest to the red LED) and moving upwards, the typical distribution is as follows:
Pin 1 – GND (common, ground): Ground reference for the entire board. This is where the grounds of the power supply, coin mechanisms, counters, and the JAMMA or IPAC board are connected. It is the common point at which all voltages are measured.
Pin 2 – +12 V: This is the main power supply for the circuit 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 12V 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 credits 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 (+12V for actuators and +5V for logic).
Pin 6 – Pulse output to coin counter 1: Each time the board registers a coin corresponding to coin slot 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 slot.
Pin 7 – Pulse output to coin counter 2: It works the same as the previous one, but for the second coin slot. It allows you to keep an independent record of the coins that enter through each slot or coin type.
Pin 8 – Coin pulse input in Coin Mechanism 1: This is where the first coin acceptor's pulse output or switch is connected. When a coin is inserted, the acceptor 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 Mechanism 2: Equivalent to the previous one, but associated with the second wallet. It allows working with two different coin channels (for example, two different values or two physical slots).
With this structure, every time a coin activates the switch in your coin purseThe 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
One very interesting detail about these classic installations is how they take advantage of the JAMMA board COIN1 and COIN2 inputsIn 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 through pin 3 The output to COIN1 corresponds to the actual coins, that is, what the player pays. Each burst of pulses is equivalent to a number of credits and is also reflected in the coin counters through pins 6 and 7.
For its part, COIN2 is used as a “service credit” entryThe service button, connected to that 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 avoids 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 actual coin inflows.
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 credits plate, nowadays it is very common to use a electronic coin selector such as the HX-916 modelwhich 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 allows recognize up to 6 types of programmable coinsThis means you can show it, for example, 6 different coins (different denominations or coins from different countries) and the 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.
With these variables and a internal statistical algorithmThe device determines if the coin is valid and what pre-programmed type it corresponds to. It also allows the selection of different accuracy levels so that the system is more or less demanding when accepting coins.
Once a valid coin has been identified, the HX-916 generates a pulse sequence at its outputThe duration of each pulse is configurable between approximately 30 and 100 ms, and the number of pulses depends on the type of coin: for example, a 1 unit coin can generate 1 pulse, a 2 unit coin 2 pulses, etc.
With its pulse output, this selector fits perfectly with credit boards, microcontrollers or JAMMA/IPAC type boardssince all these systems are based precisely on counting pulses to determine the assigned credits.
Technical specifications of the HX-916 selector
From an assembly standpoint, the HX-916 behaves as a fairly simple module to integrate, with a Technical specifications designed for intensive use in arcade machines, vending machines and similar:
- 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 telephonesIn 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.
Thus, 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 available, such as the example available in public repositories (for example, hxlnt/arduino-coin-acceptor), which show how to read and process those 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 a coin in MAME.
Physical connection: power supply and pulse cable to Arduino
In terms of hardware, a novice user usually asks themselves the main question where to connect the pulse cable and how to power the coin acceptorA typical scheme might be the following:
On one hand, the coin acceptor (such as the HX-916 or a similar model) is powered by 12 V DCIt is perfectly possible to use a 12V LED strip power supply, provided it supplies the necessary current (approximately 350mA operating current plus a safety margin). These adapters typically come with two output wires (positive and negative) that connect to the 2-pin power connector of the adapter (respecting polarity).
This 2-pin connector, on many acceptors, corresponds to a 12V electromagnetic valve or solenoidThis valve is responsible for blocking or allowing the coin to pass through. Applying 12V releases the mechanism, allowing the coin to fall and be validated. While the selector is active and powered, this valve works in coordination with the internal recognition system.
Furthermore, the acceptor pulse output The signal is connected to a digital pin on the Arduino. Ideally, use a pin with an interrupt (2 or 3) and configure the sketch to detect pulses on that pin. It is also essential to connect the ground of the acceptor (12V GND) to the ground of the Arduino (5V GND) so that both share the same electrical reference.
As for the exact point on the board where the pulse cable connects, it is usually identified as COIN, OUT, SIG or similar at the acceptor. From there, via the included cable, it is connected to the Arduino pin defined in the code. It is advisable to check the manufacturer's datasheet or PDF (for example, documents like "letpos pro" in PDF format) 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 interface between the coin acceptor and the PCThe most direct way is to connect the board to the computer via USB and have the Arduino send data through the serial port, which some software on the PC can then interpret.
However, if you're looking for something more transparent to the system, many hobbyists modify the code so that the Arduino simulates keyboard keystrokes when a certain number of credits is reached. For example, it can be programmed that, after receiving a pulse or a set 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 emulatorwithout needing to modify the PC 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 the ATmega328P with ATMEGA16U2 for USB) are very practical in this regard, as they behave like a standard serial port or, with certain modifications, even as an HID device capable of emulating a keyboard.
Manufacturer warranties, quality, and documentation
When buying a pulse coin machine board or coin selector, especially if it's for commercial use, it's important to look at the guarantees and conditions offered by the manufacturer or supplierMany reputable manufacturers offer:
Un quality supervision team 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 of controlled delivery timesThese terms are typically negotiated with the customer or set for short periods (e.g., 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 offer good value for moneyincluding OEM and ODM options. This means they can manufacture custom modules to your specifications, with the same quality standards and strict batch control for large quantities.
Another key point is the after-sales service and logisticsSome manufacturers guarantee ongoing after-sales support and offer professional worldwide shipping, which is useful if you assemble machines for different countries or manage geographically distributed amusement parks.
Regarding documentation, they usually offer PDF manuals (such as those available through links like letpos pro in Spanish) which detail connections, pin assignments, coin programming procedures, and adjustment parameters. Having that manual on hand greatly facilitates setup, especially for knowing what each dip switch or connector does without having to figure it out with just a multimeter.
Both the credit card reader and the pulse coin selectors form a fairly coherent ecosystem: The physical currency 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 is possible to set up anything from a very basic home arcade machine to complex payment systems with various types of coins, independent counters, and service buttons to adjust incidents without disrupting the collection.