Hey all,

I have been searching for weeks for information about how to make a simple (or not so simple im finding) interface between a vending machine (MDB Plug) and a com port for a pc.

the vending machine MDB Plug has the following connections on a 6 pin plug.

1 = Power Output 34 VCD
2 = Power Return
3 = Not Used
4 = Master Recieve (Min. input current (active) 15 mA @ 1 V)
5 = Master Send (Min. Source current (active) 100 mA @ 4 V)
6 = Communications Common

All i would like to do here is see the data coming from the MDB plug and eventualy write a small program to send data back to the vending machine.

my problem here is im not entirely sure where to even start on a project like this. im new to the electronics side of things and would like some advice more then anything on exactly what im dealing with and where to start out finding the information on a project such as this.

thank you so much for any advice offered.

 

You would need to find out what the serial commands are to communicate with the vending machine in software or it will be all for nothing in the end. Maybe ask the manufacturer for the protocal or something.

 

Correct. the manufactures have this information and are very cooperative in providing it. my problem is more in the way of the acctual building of the link between the machine and the pc.

 

Assuming the protocol is RS232, is the vending machine using TTL/CMOS voltage levels (0 and +5V), or -12V and +12V logic states?

__________________
Spency.

PIC Micro's - Your mind is the limit

PIC's and interfacing with other devices - a PIC Basic Guide @ digital-diy.net

 

No, the vending machine does not use the mentioned voltage levels or logic states. and there in lies the problem im having. the vending machine is using the MDB/ICP Standard (Multi-Drop Bus / International Communications Protocal Interface Standard).


My problem is that im not real sure where to start. I have requested and recieved information from the vending manufacturers on the MDB/ICP Standard (close to 400 pages worth), see first post for specifics on the connection itself. I also found that the data itself is being transmitted in Byte Format like the following:

Baud rate 9600
1 start bit
8 Data bits
1 Mode bit
1 Stop bit

11 Bits total

does this clarify the situation at all?? sorry for the very beginner like post. any help i can get would be great.