#Cable Length

1 messages · Page 1 of 1 (latest)

violet kettle
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Hello, I'm wondering what the recommended max cable length would be if I had brightness at 0% with Tachyon on. I'm wondering specifically for a 550 cable (26/28AWG).

cerulean oysterBOT
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inner hemlock
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I am unsure about recommending a cable length with:
Tachyon enabled
Brightness at 0%

For third-party cables, the only advice I can give is to try to keep them under 2 meters or lower but can try with longer but no guarantee

For reference, the cables that come with the keyboard are USB 2.0, 1.8 meters (6 feet) long and are rated for 100% brightness/tachyon mode.

Personal note: I have a total cable length of 2.4 meters with the 'Wooting Two HE,' and it works fine with 100% brightness and Tachyon disabled. However, with Tachyon mode enabled +100% there is problems.

prisma rover
full pewter
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yes

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stock cables are rated to do that

prisma rover
full pewter
prisma rover
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I did not know that I could click this

image.png
full pewter
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LOL

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its fine a lot of people take some seconds to see that too

prisma rover
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Well, thank you!!

rose thorn
# violet kettle Hello, I'm wondering what the recommended max cable length would be if I had bri...

For 0% brightness any cable up to the specification should do the job. A USB 2.0 cable is typically limited to 2 m to met the requirements (like data integrity). There is no length limit per se, this is just a result because a longer cable would likely not met the needed requirements anymore.
I forgot the correct value but the overall resistance for the power lines should not exceed 70 Ohm mV as far as I remember (of course with the maximum applied load). But that includes the joints too.

violet kettle
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The 70 ohms is good info. thank you

rose thorn
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Only if a higher brightness than 77% (or 70% if Tachyon is enabled) is used the cable and host needs to be better than the stanadard.

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The maximum allowed current for USB 2.0 is just 0,5 A.

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Vendors typically have some over provisioning but that can differ a lot.

rose thorn
violet kettle
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That'd make sense. Mech Cables told me 10ft or less, but I was hoping for 11ft 😂

rose thorn
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Sorry, I need to look it up. 70 mV seems a bit less, maybe it was 0,7 V (but that is too much).

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  • The maximum voltage drop (for detachable cables) between the A-series plug and B-series plug on VBUS is 125 mV (VBUSD).
  • The maximum voltage drop for all cables between upstream and downstream on GND is 125 mV (VGNDD).

See "7.2.2 Voltage Drop Budget" on "Universal Serial Bus Specification Revision 2.0" (usb_20.pdf) from here: https://www.usb.org/document-library/usb-20-specification

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That of course differs for a USB-C connector, but because the Wooting is just a USB 2.0 (complied) device you only need to met that specification and so can consider the USB-C side the same as the B series plug.

violet kettle
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I might be able to test it on my own by extending the usb cable. will give that a shot

rose thorn
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So because a high powered device is allowed to draw up to 0,5 A the overall cable resistance for the power lines should not exceed 0,25 Ohm (0,125 V / 0,5 A).

rose thorn
violet kettle
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wouldn't the keyboard have a threshold that automatically shuts it off when it gets too low?

rose thorn
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No, I'm not aware of any USB device which does it.