Reference Guide

MDB connector Pin Out

MDB vending machine connector’s pin out

Introduction to MDB

MDB is a communication standard used in the vending machines industry to interlink numerous devices used in a vending system. It is one of the common standardised vending used around the world today. You can typically find this MDB connector connection in the following types of machines.

  • Cold/Hot Drinks Vending Machines
  • Toy Catchers Machines
  • Coffee Dispenser Machines
  • Packet Snacks Vending Machines
  • Hot Food Baking Machines

Another vending standard is VCCS. It is adopted by the vending industry in Japan. Vending machine from Japan manufacturers typically uses VCCS instead of MDB interface standard.

MDB Connector details

Peripheral Connector

Molex Mini-Fit Jr 5569 Series, 6 ways (buy part number: 39-30-1060)

Available from Digikey part number: WM1353-ND

Master (VMC) Connector

Alternative connectors available

Tools Accessories

  • MOLEX 11-03-0044 Extraction Tool for Mini-Fit Jr Crimp Terminals
    Available from Digikey: WM9918-ND

MDB Communication Protocol Documentation

Also known as MDB ICP (Multi Drop Bus, Internal Communication Protocol). The following are the details containing the communication protocol standard used on the MDB connection interface.

Serial Communication Configuration:
9600bps NRZ, 1 Start Bit, 8 Data Bits, 1 Stop Bit, 1 Mode Bit, no hardware handshaking. 0-5V signal (TTL level).

The mode bit is a special 9th bit in the communication protocol, acting as an indicator to finish up an ongoing communication.

MDB Interface Circuit & Signal

The MDB interface is in a pull-up pull-down voltage and open-collector configuration. This allows the interface to other devices without being too much affected by the voltage system that the other devices are deployed with.

MDB interface circuit & signal

The signaling is pretty similar to the serial communication UART. You can implement MDB using the UART from the microcontroller. MDB protocol has a mode bit that uses the 9th bit of the UART serial protocol standard.

For data monitoring of this special serial data with a 9th bit, you can use Docklight serial terminal software to view. The software allows the configuration of the 9th bit. This allows you to monitor the MDB data communication. Not all the terminal software on the market allows configuration for the MDB communication protocol.

The VMC (or master device) controls the communication, to poll for slave response. Response from the slave device must be within a time frame of 5msec.

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Cable Wire Size and Current Capacity Rating Guide

This is a general cable wire size guide to help you choose the correct wire size for your electrical project.

Choosing a thicker wire provides higher current carrying capacity. It is safer to use thicker wire to conduct the current, but thicker wire is going to cost more. This guides provides you a gauge to select the most appropriate cable size.

The variety of cable brands varies in quality. The cable current conducting material and the insulation jacket material do have an impact of the amount of ampere current that a wire can conduct. The cable length and temperature of the conducting environment also plays a part. A good conducting material has lower resistance or better conductivity, produce less heat, therefore can carry more current. A good insulation jacket that can endure higher heat can handle more current before the jacket gets melted and fails.

*** Important Notes: The following wire size and current is only an estimate for a quick reference guide when selecting your cable size. It is important to check on the datasheet of the cable directly from the manufacturer. It is recommended to provide more buffer to the current capacity for your application.

Wire Size and Current Rating Table Guide

This wire size and current rating table provides a quick lookup table for your cable selection.
It is recommended to use a wire capacity that is 2 times of what your application is expecting to use.
If you want a more detailed computation, check out the next section for the calculation.

Projected Maximum
Operating Current		Wire Size
(AWG)		Copper Wire
Diameter Ø		 Cross-sectional
Area		Current Capacity
(estimated)
0.1A
0.3A
0.5A30AWG
Wire Wrapping wire		0.3mm0.05mm20.8A
1A28AWG0.36mm0.08mm21.25A
2A27AWG
3A26AWG0.46mm0.14mm23.5A
5A24AWG
CAT5e Network Cable		0.61mm0.2mm25A
22AWG0.78mm0.33mm28.73A
10A21AWG
20AWG0.92mm0.5mm213.87A
25A17AWG1.34mm1.06mm229.2A
16AWG1.31mm2 (closest 1.5mm2)
50A14AWG
Electrical Wire		1.78mm2.07mm2 (closest 2.5mm2)55.6A
12AWG
Electrical Wire		about 4mm2
10AWG
Electrical Wire		about 6mm2
Table: Estimated wire current carrying capacity.

Calculate current capacity and voltage drop

For application that cannot afford for thicker wire with higher current capacity, it is important to calculate close to your projected situation. We will need to know the amount of current the wire can carry, as well as the expected drop in voltage over the wire distance (to and from).

Wire conducting material and their resistivity.

Wire MaterialResistivity per metre
Copper0.0174 μΩ.m1.724 x 10-8 Ω.m
Aluminum0.0265 μΩ.m2.65 x 10-8 Ω.m
Silver0.0265 μΩ.m2.65 x 10-8 Ω.m
Carbon0.1 μΩ.m10 x 10-8 Ω.m
Iron0.1 μΩ.m10 x 10-8 Ω.m
Table: Wire material resistivity

The formula to compute the resistance of a particular wire material is base on normal room temperature of 20 °C.

Resistance, R = ρ L / A Ω

where
R = resistance of the conductor (ohms, Ω)
ρ = resistivity of the conductor material (ohm metre, Ω m)
L = length of conductor (m)
A = cross-sectional area of conductor (m2)

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