Paleocord Adapter 1 board for RJ45, RJ14/RJ25, USB, and phone jacks

(See also related blog posts about this adapter; all Paleocord adapters.)

Paleocord Adapter 1 is a circuit board that permits the somewhat proper interconnection of RJ45 TIA/EIA-568A wiring standard to RJ14/RJ25 landline phone jacks, USB cables, and phone jacks.

The current version has been tested. The most recent KiCAD source file archive is v1.21, 2016-Dec-4. (I'll need to check the KiCAD version number.) It is also available for purchase directly from OSHPark.com.

At the top of the board are 4 RJ45 jacks in a row. In the middle is 8 solder pads to connect to each wire. Along the each side is a micro-USB-B jack and USB-A jack. Along the bottom is a pair of 3.5mm monaural phone jacks, a pair of RJ25 jacks, and a second pair of 3.5mm monaural phone jacks.

The following parts fit right in; other variants will likely work fine too.

The wiring cheat-sheet is as follows. I used the notation "tip(ring)" for pin numbers so "5(4)" is pin 5: tip, pin 4: ring.

My immediate need was to manage in-house wiring since I sometimes need a phone jack, or want extra 100BASE-TX jacks. I just ran a bunch of cabling in my house, and have come to favor Category 5e … basically because I got about a thousand feet of it for free. It's actually pretty nice with a bandwidth of 100MHz to permit everything from low DC power to 1Gbps 1000BASE-T Ethernet. I've used it so far for Ethernet and phone, but it should be capable of handling USB 2.0 data for short runs, and certainly for low-power audio speakers (e.g. with an 8-ohm speaker, a pair of 15-foot (5m) 24ga wire is about 1 ohm, so about 13% loss in the wire).

So I figured I'd like to make an adapter to break out the RJ45 jack into the TIA/EIA-568 wiring pairs and then reconnect them to other kinds of connections in a rational way.

Let me take a moment for bit of history and go back to 1878 when manual telephone exchanges began using 1/4" phone jacks to plug between lines. They designated the two circuits "tip" and "ring" to refer to the conductor at the tip of the connector, and the long metal shield forming a ring around the center conductor. About a hundred years later, the U.S Federal Communications Commission (FCC) instituted a standard for interconnecting telephone equipment and the registered jack (RJ) was formed. The RJ25 can house 6 circuits whereas the RJ14 has 4 and the RJ11, 2, although all the plugs are physically cross-compatible. This translates to 3 phone lines in an RJ25, 2 in an RJ14, and 1 in an RJ11. The wiring is as follows:

As you can see, the tip and ring nomenclature continued.

The 8P8C RJ45 jack adds one more pair. Per the TIA/EIA-568 standards, the pairs are identified by color with the striped white wires designated "tip" and the solid colors "ring". Blue is pair 1, orange is pair 2, green is pair 3, and brown is pair 4. Delving into the 10BASE-T and 100BASE-TX Ethernet standards, pair 2 (orange) is for receive and pair 3 (green) is for transmit with rings being negative and tips being positive in the differential pairs. The difference between TIA/EIA-568A and TIA/EIA-568B is simply that the position of pair 2 and pair 3 are swapped in the connector, permitting a crossover cable. As such, pairs 1 and 4 are unused in this kind of signaling.

Now, back to the Paleocord Adapter 1 …

Starting with the RJ45, the adapter board has two of them connected directly in parallel to permit chaining cables together. I designated pairs 2 and 3 "main" and pairs 1 and 4 "auxiliary" (aux on the board). The right side of the board is for the "main" pairs, so the right-side RJ45 jack leaves pairs 1 and 4 unconnected, and pairs 2 and 3 are connected to the central jacks. The left side is for the "aux" pairs, so the left-side RJ45 also leaves pairs 1 and 4 unconnected but its pair 2 is wired to the central jacks' pair 1 and its pair 3 is wired to the central jacks' pair 4.

The result of all this is that the two central jacks are tied together while the right-side one will only connect the 10BASE-T and 100BASE-TX Ethernet pairs. The left-side "aux" jack connects those Ethernet pairs to the auxiliary pairs in the central jacks, so you could actually run two 10BASE-T or 100BASE-TX Ethernet cables down one Category 5 cable connected to the central jacks.

Working backward in time, the RJ25 jacks are likewise connected to the main and aux pairs in the central jacks. On the main side, line 1 goes to pair 2, line 2 goes to pair 3, and line 3 goes to pair 1. On the aux side, line 1 goes to pair 1, line 2 goes to pair 4, and line 3 goes to pair 2. All tip and ring polarities are maintained. Note that using an RJ14 or RJ11 socket or cable would mean that line 3 is ignored. I connected it only because I had a use for 6-position cables and it violates the main/aux designation on the board since "main" L1 is connected to "aux" L3 and "aux" L1 is connected to "main" L3.

Going way back to 1878, the main and aux pairs are also connected to phone jacks. Well, not technically 1878 because I went with 3.5mm jacks instead so they'd fit in a smaller space rather than proper 1/4" jacks. Left-to-right, it's aux pair 1 and pair 4 then the two RJ14 jacks, then main pair 2 and pair 3. Being all tidy, the tip and ring (well, shield) are also connected properly. In theory with a 3.5mm to 1/4" adapter, one could patch a modern RJ14-connected phone right into a 1878 switchboard.

Finally because I had the space, I threw on a couple USB connectors: a micro-USB-B jack and a USB-A jack, properly connected together (there is a jumper to connect the micro USB On The Go pin to ground, which would indicate to the connected device to act as a USB host rather than a USB device). The main USB jack is wired so D+ and D- use the tip and ring of pair 2 and +5V and ground use the tip and ring of pair 3. Likewise the aux USB jack connects the data to pair 1 and the power to pair 4. If nothing else, this is an easy way to get a few tens of milliamps of 5V power to a remote location riding next to two pairs of other signaling. I don't think it's practical to run USB, but the data lines are connected, and I figure a meter or two of cable would probably work.

The board is cut so it should fit right into an Altoids tin. Notch holes where you need and it should work fine. Do note that all the shields and the mounting holes are electrically isolated. This is of particular concern with the USB ports as the shield is generally connected to ground, so one might unintentionally short pairs together (e.g. pair 3 ring and pair 4 ring are USB ground.)

The board has a bit of instructions on the silkscreen, visible even after its fully populated. I did include one caveat on the back: "THIS BOARD DOES NOT MEET ANY STANDARDS AND IS NOT INTENDED FOR CRITICAL APPLICATIONS." And I mean it. I tried to make the connections useful, even routing the pairs parallel to one another as much as possible, and keeping pairs separated as much as possible. But it will probably cause some packet loss, and running mixed signals in the cable will probably cause some unexpected interference.