// Solder Spec Sheet
USB Cable Pin Configurations
Wiring reference for hand-soldered keyboard cables — 4-, 5-, and 6-pin detachable (FEMO / LEMO) builds. Follow the standard below; verify against your connector PCB before soldering.
WIRED INRev. 2026
Wire Color Standard
1GNDBlack
2D+Green
3D−White
4PWR (VBUS)Red
5CC / GND2Blue
6PWR2Yellow
Pin numbers follow the numbered 1B insert. Pins 1–4 are the USB 2.0 standard and never change. Pin 5 (blue) and pin 6 (yellow) hold a fixed wire color — their function depends on the configuration below. D+ / D− are a single differential pair and are never doubled.
How USB-C Detection Works (the CC line)
A USB-C device won't power on just because 5 V is present — it has to detect a valid partner through the CC (Configuration Channel) line first. That's why a bare 4-pin cable can be hit-or-miss on USB-C.
USB-A → USB-C: the A host has no CC pin, so the cable must present a 56 kΩ resistor from CC to VBUS so the C device sees a legacy host and draws power.
USB-C → USB-C: the host watches CC for the device's 5.1 kΩ pull-down (Rd). The cable must carry CC through (or the connector must supply Rd onboard) or the host never enables VBUS/data.
CC1 vs CC2: USB-C is reversible — only one CC is live per orientation, so we wire a single line labeled simply CC.
4-PIN · USB 2.0 Standard
USB-A→C · USB-C→C
| Pin | Signal | Wire | Notes |
|---|
| 1 | GND | Black | Ground. |
| 2 | D+ | Green | Data pair. |
| 3 | D− | White | Data pair. |
| 4 | PWR | Red | +5 V VBUS. |
USB-C→C as 4-pin only works if the connector supplies CC onboard (see note below). On USB-A→C, the C end still needs the 56 kΩ CC pull-up to be reliable.
Optional — proper USB-C shield: run GND / D+ / D− / PWR on the front of the USB-C PCB and land the braided shield as a second ground on the rear pad.
5-PIN · adds CC
USB-A→C · USB-C→C (non-fast-charge)
| Pin | Signal | Wire | Notes |
|---|
| 1–4 | GND · D+ · D− · PWR | Blk/Grn/Wht/Red | Standard USB 2.0 (as above). |
| 5 | CC | Blue | A→C: 56 kΩ pull-up CC→VBUS (legacy-host detect). C→C: carry CC through for sink (5.1 kΩ Rd) detection. |
The 5th pin is what lets a USB-C→C link be recognized — a 4-pin C→C often won't enumerate without it. Genuine LEMO has true 5-pin inserts; for non-genuine 5-pin, use a 6-pin insert and leave pin 6 empty.
6-PIN · Fast Charge
USB-C→C only
| Pin | Signal | Wire | Notes |
|---|
| 1–4 | GND · D+ · D− · PWR | Blk/Grn/Wht/Red | Standard USB 2.0 (as above). |
| 5 | GND2 | Blue | Second ground — doubled for current capacity. |
| 6 | PWR2 | Yellow | Second +5 V — doubled for current capacity. |
Pins 5 & 6 double up ground and power for higher fast-charge current. At the device end, bond GND+GND2 → one ground and PWR+PWR2 → one +5 V. CC detection is handled by the resistor on the connector PCB.
Pin Cup Orientation
Looking at the solder cups with the keyway / red dot held up. The female face numbers clockwise from just right of center; the male face is its mirror (counter-clockwise from just left). The keyway is your reference — count from it every time.
6-PIN · fast charge (even hexagon)
The keyway centerline sits between pins 1 and 6.
5-PIN · 6-pin insert, one cup empty
We use a 6-pin insert and leave pin 6 empty (dashed). ⚠ In male / reverse orientation it's easy to mis-fill — you are not filling every cup like a 4-pin, so count from the keyway each time.
Connector PCB Pads
Where each wire lands on the USB connector's own solder PCB. ⚠ Representative — pad order and labels vary by connector (PWR may read VCC / V+ / 5V; CC may read ID; some boards split GND/PWR to the reverse). Always solder to the labels printed on your PCB.
USB-A · 4 padsSolder side
USB-C · front pads (5-pin shown)Solder side
6-pin (fast charge): same front pads + GND2 (blue) · PWR2 (yellow) on the reverse, doubled for current. 4-pin omits CC — the onboard chip handles it.
CC Resistor — On the Connector
Our USB-C connectors carry the CC resistor on the connector's own PCB (confirmed on the fast-charge connectors — there's a small chip on the board). That's why a "4-pin" solder can still enumerate, and how the 6-pin handles detection while pins 5/6 do power.
If a build is inconsistent across machines, the CC resistor is the suspect — missing, wrong value, or a host that strictly enforces CC. To wire CC by hand instead: 56 kΩ to VBUS for A→C, 5.1 kΩ to GND on the C-sink end.
