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Topic: Multiplexing to 48  (Read 171 times) previous topic - next topic

chesterthompson

Hi

I am currently in the process of building a machine for identifying cables. My plan is to use an Arduino to send out 48 different signals basically simultaneously (By very quickly cycling through all 48 cables). So I am thinking multiplex 48 times, which should not be hard. On the other end of the cable you will plug in a small serial LCD and you will get a cable number reading. Because I am only sending tiny amounts of data the Baud can be slow i think. The only problem is that these cables could be up to 100m long. These will be CAT5 cables.

From what I understand you are not able to use the RS485 and such because of the negative swing which wouldn't work with normal multiplexers.

So either send signal without any drivers at a low rate say 2400Baud, but I am not sure if this will work and the signal would just get scrambled

Or somehow find a way to multiplex RS485 signals.

I am also trying to do this on a budget

Any help would be much appreciated.


Thanks

PaulRB

#1
Jul 17, 2017, 08:50 pm Last Edit: Jul 17, 2017, 09:11 pm by PaulRB
Do you mean 48 cat5 cables, or 6 cat5 cables which contain 8 cores each, totalling 48 cores?

What is the purpose of this project? Continuity testing of all 8 cores in each cable? Identifying which cat5 cable is which? If so, why do you need to send data?

I'm going to take a guess. 48 cat5 cables go into the wall/floor/ceiling in one room. 100m away, those 48 cables come out and you need to identify which is which. There's only you with no one to help and you don't want to have to keep going from room to room over and over. I can think of a way to do that without an Arduino.

chesterthompson

Hi

Thanks for your reply. You guessed right except each Cat5 cable goes to an individual room. Arduino was just the best solution I could think of.

So there are 48 individual cables

Any ideas would be great

Thinking of sending a number down each cable then reading it from an LCD

PaulRB

Presumably the cables in each room will be fitted to an rj45 wall socket?

First two questions: 1. Is it worth building anything if you will only repeat this exercise once? 2. Why do you need to identify the 48 cables anyway? Won't they will be plugged into a 48 way network switch, in which case why do you care at all which is which?

Anyway, my idea is this:

You make 48 "identifiers" which consist of a simple rj45 plug and an offcut of cat5 cable. The 8 wires are connected to each other differently in each case, giving each one a unique code. One wire is designated the "ground" or "common" wire. The other 7 are arranged in a group of 4 and a group of the remaining 3 wires. Within each group, a binary combination of the wires are connected to the common wire. The others are left unconnected. The group of 4 wires can represent a number on the range 0 to 9. The group of 3 wires can represent a number in the range 0 to 7. This gives 70 possible combinations, of which you only need 48. You plug one of these "identifiers" into the socket in each room.

Then you build a relatively simple board to read that code from the other end of the cable. The board has 2 single digit 7-segment displays and 2 BCD to 7-seg decoder chips, plus a few pull-up resistors. You plug this into one of the cables, and the BCD decoders read the connections on the "identifier" at the other end, and display the two digits.

So that's my idea.

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