Vending Basics for New Operators
How MDB works in a vending machine.
MDB is the shared connection inside a vending machine. The controller uses it to run the coin mechanism, the bill validator, and a card reader as one system. Here is how a sale moves across it.
One controller and several devices on one connection.
MDB, short for Multi-Drop Bus, is the vending industry’s standard way to connect payment devices to a machine. The vending machine controller is in charge. The coin mechanism, the bill validator, and a card reader each plug into the same bus, and the controller checks in with each one in turn, over and over, while the machine is on.
Every device has its own address on the bus, so the controller always knows whether it is hearing from the coin mechanism, the bill validator, or the reader. The Standards page covers MDB beside the other standards Dryline uses.
How a cash sale moves across the bus.
The bill goes in
The bill validator accepts a dollar and tells the controller how much it took.
The controller adds credit
The display shows the credit, and the customer keys in a selection.
The product vends
The controller turns the coil, then tells the coin mechanism how much change to pay out.
How a card sale moves across the bus.
The customer chooses
The controller sends the selection’s price to the card reader, which asks for a card, phone, or watch.
The reader approves
The reader tells the controller the payment is approved, and the controller turns the coil.
The controller reports back
It tells the reader whether the vend succeeded. The reader completes the sale, or cancels it after a failed vend.
That order is Select First. The reader can also take payment before the choice, or one payment for several items: the vend modes guide explains both.
Cash and cards work side by side.
Adding a card reader takes nothing away. The coin mechanism and bill validator stay where they are, and the reader joins them on the bus, drawing its power from it. Customers pay with whatever they have.
How to tell if a machine has MDB.
Look at the coin mechanism and the bill validator. If they are MDB units, which most are, the bus is already in the machine. The MDB harness ends in a six-pin connector inside the cabinet, usually already feeding the coin mechanism.
MDB has been the standard for decades, so most snack, beverage, and combo machines built in roughly the last twenty years support it. Rain Pay works with most modern vending machines that support MDB cashless. There is no retrofit for a machine that cannot take MDB cashless, so check before you buy a used machine.
DEX keeps the machine’s own sales record.
MDB carries payments. DEX is a separate port where the machine counts what it sold from each selection. The Rain Pay reader (a Dejavoo QD3) reads DEX automatically, so Dryline can check the machine’s own count against its dispense records and what settled, and flag anything that does not match.
Questions about MDB
- Is MDB the same as DEX?
- No. MDB connects the controller to the payment devices and carries every payment. DEX is a separate port that holds the machine’s record of what it sold.
- Does the card reader need its own power supply?
- No. The Rain Pay reader takes its power from the MDB bus, the same way the coin mechanism and bill validator do. There is no extra cable to an outlet.
- What does the controller do in a vending machine?
- It runs every sale. It reads the keypad, turns the coils, and decides when to ask the payment devices for money. The coin mechanism, bill validator, and card reader all answer to it.
More vending basics.
Why offer cashless
What card and phone payments add for customers and for you, and what a machine needs to take them.
Tap to Start, Select First, and Multivend
Pay first, choose first, or buy several items with one tap, and why your machine has a say.
Planograms
The map of a machine: what goes in each slot, at what price, and how full to fill it.
Stocking strategies
A first product mix, par levels, rotation, and restocking the machines that need it.
Starting a vending business
Licenses, sales tax, insurance, machines, locations, commissions, pricing, and routes.
Put a card reader on the bus you already have.
Book a 20-minute demo and see a card vend reach Dryline, tied to the product that dropped.