This writeup serves to provide a full, transparent index of our material specifications & all technical details that lay the foundation for our cable builds. We believe in information sharing and encourage your perusal before designing your cable.

Table of Contents

1. Power Delivery, Length & Coils

USB specification requires voltage to stay between a prescribed range after power loss over distance (i.e. length of the cable). Most custom mechanical keyboards are relatively low power devices and will be sufficiently powered by any cable configuration that does not exceed a maximum total physical length of the specification-defined 16.4 feet / 5 meters.

In some instances, the presence of onboard LEDs may come with a significant increase in power demand. With total physical lengths at or near the maximum allowable 16.4 feet, well-engineered keyboard PCBs designed by established and reputable designers (such as hineybushWilba, and Gondolindrim, among others) will function without issue by prioritizing the keyboard matrix before any LEDs, sometimes resulting in slightly dimmed lighting but at no cost to the keyboard's typing input function.

For brightly-lit keyboards without proven track records or with limited PCB information, consider this a "your mileage may vary" disclaimer due to our inability to acquire and test the vast range of keyboards on the market; as such, you may wish to opt for a shorter total physical length of 12 feet or less.

As a special note, there are several community-documented standout models that are known to require substantial power; the most commonly noted are the HHKB, the Input Club K-Type, and the Drop series boards (ALT, CTRL, and SHIFT). Cables for the HHKB should be no longer than a total physical length of 8 feet, or 6 feet if using the onboard USB passthrough for your mouse. For the remaining models, we recommend a maximum total physical length of 10 feet.

Coils

Coils add a significant amount of extra physical length based on their diameter. To calculate your build's total physical length, add the below coil physical length value to your chosen cable length.

Small Diameter Coils

  • small 6 inch coil: +4 ft physical length
  • small 8 inch coil: +5.5 ft physical length
  • small 10 inch coil: +7 ft physical length

Large Diameter Coils

  • large 6 inch coil: +5 ft physical length
  • large 8 inch coil: +7 ft physical length
  • large 10 inch coil: +9 ft physical length

      Example: 6 ft cable length + large 6 inch coil (5 ft) = 11 ft total physical length

      Default Length Diagram (unit: inch)

      • cable length = a + x + z OR b + x + z
      • coil length = c = 6, 8 OR 10
      • default x = 2
      • default a = 5
      • default b = 2

       

      Figure 1: default length diagram 

       power delivery and length diagram

      For technical reference on a simplistic level, internal cable testing shows a total physical length of 16.4 feet / 5 meters is capable of providing up to approximately 440 mA at the USB specification's minimum allowable voltage of 4.40 V when drawing power as the only downstream device connected to any desktop motherboard USB header. Do note, however, that these measured values may vary with different hardware setups.

      2. Coil Methodology

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      The coiling process may be a deceptively complex subject in achieving robust, long-lasting coils that resist deformation over time with standard use, including daily pulling and stretching as needed to move the keyboard around the desktop. We delve deeper (with video footage) into our HELIX coil method on the Coil Durability sub-page.

      3. Connector (In)compatibility

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      We cannot guarantee our cables are compatible with those of other vendors. Each vendor uses a proprietary pinout for their quick disconnect (QDC). Please take the necessary precautions before attempting to mix and match cables from different vendors; failing to do so may result in irreversible damage to your device. Coaxius uses 5-pin models for all QDC offerings with the following pinout taken directly from the USB-IF standardized wiring order:

      • 1: VCC (red)
      • 2: D- (white)
      • 3: D+ (green)
      • 4: GND (black)
      • 5: drain/unused** (grey)
      LEMO® YC8
      LEMO GX16 YC8
      Figure 2: wiring order depicting host-side QDC solder points

       

      **By default, Pin 5 is unused. Connecting the drain wire to maintain shield continuity throughout the cable's full length is considered good practice by some vendors and community members. This method, however, is not fully adequate at providing a valid Faraday cage effect across the QDC. Doing so requires 360° crimp connections, an installation method we provide through the Premium Shielding option. Further details on Premium Shielding and the shortcomings of custom made-to-order USB cables are detailed directly below.

      4. USB Specification Issues

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      Shielding Shortcomings

      The standard cable assembly used to connect mechanical keyboards to a computer is classified by the USB-IF as a detachable cable, meaning it may be hot-plugged/unplugged by the user at the device (keyboard) end. The USB-IF maintains that all detachable cables must be double shielded (mylar foil plus copper braid) throughout the full length of the cable with proper termination at the host and device plug shells. Some cable vendors labor to crimp the drain wire at the plug shells, others remove the shield at each end, and others yet even use unshielded internal cable. Although all cables employing any of the above methods will properly power a keyboard without issue in nearly all circumstances of mechanical keyboard usage, none of these methods meet USB specification.

      In order to properly shield the entire length of the cable, the copper braid must be 360° crimped at the host and device plug shells for much fuller contact than a lone drain wire offers.

      Quick Disconnect (QDC) Restrictions

      Our hobby has a penchant for splicing in-line docking connectors into the middle of the cable; while they are both functionally convenient and aesthetically satisfying, by their very nature, quick disconnects are prohibited and do not meet USB specification. However, certain variants may be installed with proper crimping methods to ensure the QDC behaves as a Faraday cage and fully shields the signal (data) wires.

      Implications

      There are no cables in the custom made-to-order space that meet official USB specification, including ours. Some offer better shielding than others, but none are fully certifiable.

      However, in 99.9% of all typical cases of mechanical keyboard usage (offices & homes), custom cables built by us or any other leading vendor in the hobby space will be perfectly functional without fail. Unlike monitor signals across DisplayPort or HDMI cables, by contrast, keyboard signal integrity has a nearly nonexistent risk of data corruption.

      For those whose workspace demands the full, robust shielding detailed in the USB specification, or for those who settle for only the best, we offer the option to upgrade your cable to Premium Shielding.

      Premium Shielding

      Premium Shielding is our installation method that enables your cable's shielding to function on a technical level as if it meets USB specification, sufficiently blocking transmission of excessive electromagnetic interference to and from the cable via 360° crimp connections and the subsequent Faraday cage effect. Note that this is not the same as official laboratory certification; if your use case requires official certification, we strongly advise against using any one-off custom made-to-order cables.

      Note: Premium Shielding is only available on cables without a QDC, or those with LEMO® connectors.

      5. Materials & Specifications

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      Cable - USB compliant, double-shielded, four-conductor cable

      • Power Conductors: 28 AWG x 2
      • Data Conductors: 28 AWG x 2 (twisted pair)
      • Foil Shield: aluminum mylar (≥100% coverage)
      • Braid Shield: tinned copper (≥65% coverage)
      • Conductor Resistance: max 239 Ω/KM @ 20°C
      • Insulation Resistance: min 100 MΩ/KM @ 20°C
      • Impedance: 90 Ω +/- 15%
      • RoHS Compliance: Yes

      Paracord (550 lb Type III) - inner base sleeving

      • Material: nylon or nylon/polyester

      Techflex® (Flexo PET) & MDPC-X®outer double sleeving

      • Material: polyethylene terephthalate (PET)
      • RoHS Compliance: Yes

      Heatshrinkconnector finishing material

      • Material: polyolefin
      • RoHS Compliance: Yes

      USB Connectors - standardized host and device plugs

      • Housing: nickel-plated or gold-plated stainless steel
      • Contacts: gold-plated phosphor bronze or brass
      • RoHS Compliance: Yes

      6. Quick Disconnect Form Factors

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      LEMO® the premium, zero-compromise latching push-pull connector, manufactured to classic Swiss quality control and finishing standards

      • Size: 0B / 9.5mm diameter
      • Connection: Swiss-engineered latching push-pull
      • Material: chrome-plated brass
      • Color Options: silver (standard stock), black (limited availability)
      • Source: LEMO USA, Inc.
      • RoHS Compliance: Yes

      YC8 Push-Pull a moderate quality, "easy on the wallet" connector that achieves a mildly similar aesthetic to the classic LEMO®

      • Size: 11.5mm diameter
      • Connection: pin-based push-pull
      • Material: chrome-plated brass
      • Source: OEM supplier, China
      • RoHS Compliance: No Data