How to convert coin-op and mechanical machines to card payment
Not every machine speaks MDB — coin-op laundries, car washes, water dispensers and arcade machines run on a much simpler electrical signal. Here's how pulse, dry contact and a trigger line turn those machines into card, QR and cloud-connected payment.
Almost every article about adding card payment to vending starts from the same assumption: the machine speaks MDB. For most vending machines that's true. But there's an enormous installed base in the field that speaks none of these buses — coin-op laundry machines, self-service car washes, water dispensers, massage chairs, coin-op arcade machines. They don't understand a data bus; they understand a single electrical pulse: a coin dropped, start. The good news is that by imitating exactly that pulse, these machines convert to card, QR and cloud-connected payment too.
The problem: these machines don't speak a bus
On an MDB vending machine the terminal joins the machine as a “cashless device” and holds a conversation with it: select, approve, vend, settle. On a coin-op or mechanical machine there is no such conversation. All the machine waits for is a simple signal from its coin acceptor or a relay. You don't have to redesign the inside of the machine to fit a card reader — you only have to produce the signal the machine is already listening for.
The key idea: tell the machine “a coin dropped”
The whole conversion is one sentence: when the customer pays by card or phone, the DMS terminal sends that pulse down the line where the machine expects a coin — and the machine starts running as if a coin had dropped. The machine doesn't know, and doesn't care, whether the payment came from a card or a metal coin; it only wants to see the signal it's waiting for.
Three signals, three classes of machine
In practice “a simple signal” isn't one thing but three close relatives. Which one you use depends on how the machine is started.
Pulse — coin-op machines. The terminal imitates the coin or token pulse. On payment approval it sends the pulse the machine is waiting for; the machine runs as if a coin had dropped. Typical use: laundry machines and self-service car washes.
Dry contact — relay-triggered machines. On payment approval the terminal closes a clean, dry (voltage-free) contact and bridges the machine's own start line. It doesn't push voltage into the machine's circuit; it just shorts the two ends together the way the coin mechanism would. Typical use: water dispensers, massage chairs, barriers, simple dispensers.
Trigger — start-line machines. After payment the terminal sends a single trigger pulse to the machine's start input, and the machine delivers the product or service. Typical use: coin-op arcade machines and older vending machines.
The common thread in all three is the same: the pulse is only produced after the payment is approved. If the card is declined, no signal is sent and the machine doesn't start.
If there's MDB or Modbus, we use it
These three signals come into play when the machine offers nothing richer. If a machine genuinely speaks MDB, the terminal joins that bus as a cashless device — because there you get more: per-product pricing, credit balance, a vend-approval handshake. On PLC-controlled machines we integrate over Modbus instead. So the rule is simple: whatever language the machine speaks, we join at the richest one it offers; if it speaks none of them, we produce the electrical pulse it's waiting for.
A coin-op machine joins the fleet too
The real value of the conversion is beyond the signal. Card payment is only the entry point; because the Hero Nexus software inside the machine manages the payment and produces the right signal, that same machine now connects to the QuadC cloud as well. So a coin-op laundry machine or a car wash bay becomes a machine that reports remotely — how many times it ran, how much it collected, whether it's online. Instead of counting the coin box or driving out to the site, you see the fleet in a browser.
A machine that doesn't look like an MDB vending machine isn't a machine at the end of its life. It has a line where it waits for a coin and a defined moment when it starts — it already has everything a modern payment layer needs to sit on top of. That's exactly what the Smart VMC approach is: without replacing the machine, joining it at whatever language it speaks — MDB, or just a coin pulse — and turning it into a card-paying machine that talks data.