Modular cabling idea needed for SX48 proto board and (10) SX28 proto boards.

T&E Engineer

I am working on a proto type project that is using an SX48 proto board as a master unit that will connect to as many as (10) SX28 slave proto boards. I need·a good way to make this modular·instead of·total hardwiring/soldering cables between the proto boards.

I only have 3 wires (serial, Vss, Vdd) per cable as you would see for an LCD or other serial device. The SX48 proto board master will power all of the 10 SX28 slave proto boards. I was thinking of soldering (10) short RJ-45 cut cables to the SX48 proto board. The other connector end would snap into the back of a plate mounted to the metal case that the SX48 is inside. This would be repeated with a single RJ45 cut cable and mounting plate on each of the 10 SX28 proto boards. Between the enclosed SX48 case and each of the enclosed (10) SX28 cases, I could just then snap in any length CAT-5 cable between them.

This is the idea (but a bit of a waste only using 3 of the 8 wires on the RJ-45 - but ok still). It needs to be modular to·easily replace and cat-5 cables·are easily found.

Radio Shack may have the cables but $$$ and the plate connectors which gave me the idea. However, I need to have an online order placed today or tomorrow with any other ideas.

Does anyone have a better way to do this?·Please provide links if you can. Perhaps RJ-11 ?? Where can I get the parts from to do this?

Thank you.

Dennis Ferron

I'd use .1" space pin headers. They're the same spacing as DIP pins so fit nicely on boards, and don't take up much space. I would cut up old floppy disk or 40 conductor IDE cables to get ribbon cable for the wires.

If you do use Cat-5 cable, understand that it should not be considered to be 8 separate wires - think of it as four twisted pairs. If I were you I would put Vss and Vdd through 1 pair, and serial and another Vss through the second pair. Pairing with ground ensures a good serial signal, and might even help keep noised off Vdd as well. Although it might seem like a waste to use 8 conductor cable, an experienced electronics teacher once gave me this advice: "always leave things open in your designs - extra board space, extra unused gates on TTL chips, extra wires in your cables. As an engineer you want to wrap things up and put everything in the design to use, but when you do that, you don't leave any room for unexpected changes." So maybe the extra 2 pairs in your Cat-5 will turn out to be useful later after all.

RDL2004

I would look into the RJ-11 phone connectors/cables. These should be cheap and only have four circuits instead of eight. Check at any Wal-Mart or your local home improvement store.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- Rick

T&E Engineer

Where can I get RJ11 or RJ45 snap on connectors for the·enclosure (lower cost maybe)? Remember I want to be able to use a regular RJ45 or RJ11 cable once outside the enclosures going from the master to each of the slave units.

Radio Shack sells these (but certainly open to any other on-line places for an order today):

http://www.radioshack.com/product/index.jsp?productId=2102882

OR

http://www.radioshack.com/product/index.jsp?productId=2102539

I did not see them for RJ11.

Harrison.

RJ11 and RJ45 keystone jacks should be easy to source. They are common in home networking / telecommunications setups. Worst case scenario go to Home Depot and pick some up there. I recall bgmicro.com has them for cheaper, but they are a surplus company and are sometimes slow at shipping.

If you still can't find RJ11 jacks then just use RJ45 ones. They are compatible (in fact, the center pairs are wired the exact same way). It's common now to just use RJ45 keystone jacks for everything, including analog telephones because you end up using full cat5 anyways.

It's probably a good idea to look at how RJ11 and RJ45 is wired. RJ11 for phones is not straight through. RJ45 for ethernet networking is straight through, but the wiring is not as obvious since one pair is on pins 3&6, while the other pairs are on consecutive pins. Knowing how the pairs are setup is especially important if you are doing long distance RS485 or similar.

T&E Engineer

So that's what they are called "RJ45 keystone jacks". I entered that into Google and have lots of leads.

Thanks again!