1A2 Converter: RJ-21 <-> RJ-45 Converter

These two cards can be used together to replace long runs of 25 pair cable in 1A2 phone systems with cat5 network cables instead. These are hardwired to carry 1A2 signals for Line 1, 2, 3, 5, bell and buzzers over up to three RJ45 cables. Note: The previous ExpressPCB version of this board, "REV-A", is compatible with the REV-B board shown here.

Here's the pair of finished printed boards:

"KSU" board
Plugs directly into the KSU,
and RJ45 cables run out to the phones.
"PHONE" board
These are for the "phone end" of the RJ45 cables.
Phones plug directly into this board.

On the left, a "Key System" board which handles the KSU end of the connection.

On the right, a "Phone" board which handles the phone extension end of the connection, which can optionally be multipled (bridged) to chain several extensions.

Potentially long RJ45 network cables connect the boards together (can be cat5, cat5e, etc). Each cable can carry 4 pairs of 1A2 signals. Up to three cables can be carry a total of 12 pairs.

Small 1A2 systems don't come close to using all 25 pairs of the fat telco cables, so network cables with fewer conductors can be used to carry just the minimum required signals. These boards are designed to provide the common needs of a small 1A2 system; up to 3 CO lines and Intercom (Lines #1, #2, #3, and #5):

Anywhere from one to three cables can be used, depending on how many 1A2 signals are needed, to minimize the amount cabling:

RJ45 Port Provides Details
A Line #1 + Ringer An RJ45 cable for port "A" provides Line #1 and the ringer (bell).
Line #1 T/R/A/L and Bell (Y-S pair), and two conductors for ground: total of 8 conductors.
B Line #2 + Line #3 An RJ45 cable for port "B" provides Lines #2 and #3
Line #2 and Line #3 T/R/A/L
C Line #5 (ICM) + Buzzer An RJ45 cable for port "C" provides Line #5 (usually the Intercom) and buzzer.
Line #5 T/R/A/L and buzzer (Y-O pair)

You can provide these cables in any combinations shown below. Just be sure e.g. Cable "A" goes to the "A" connector at both ends; don't mix them up!

If you need more than what all 3 cables can provide, you might as well use a 25 pair cable, because more than 3 cat5 cables is about as thick as a 25 pair cable.

If you need any other kind of wiring, use 66 blocks with amphenol on the left and RJ45 connectors on the right, so you can punch down any kind of RJ45 wiring you want.

So depending on what one needs, here are the common cabling configurations these boards were designed for:

These boards also allow you to bridge multiple phone extensions, e.g.

Single Phone Bridged Phones

Gerbers and PCB Layout Files

Here's the gerber files which you can have printed very cost effectively (e.g. PCBway).
You can then populate the boards with the components using the Digikey part numbers shown on the silk screen.

Here's the original "Sprint Layout 6" PCB .lay6 file which lets one redesign and re-generate gerber files.
Here's screenshots of what the board looks like inside Sprint 6 layout:

Top and bottom copper + top silk

Top "Photo" View

Bottom "Photo" View

Parts Notes

Note that the recommended Digikey part numbers for the three RJ-45 sockets and the separate male and female Amphenol connectors appear on the silkscreen, printed below the connectors. (e.g. "A31407-ND" below the RJ-45's, etc).

For the "KEY SYSTEM" board's right-angle amphenol connector, a "solder type" connector is the only option.

For the "PHONE" board's amphenol, either a press-fit or a solder type can be used. (Avoid press-fit unless you have a press-fit jig)

The two boards will be printed as one; you just saw down the middle with a jigsaw to separate the two boards.
Or you can specify to the printer to have them cut it for you.