Keyboards with USB passthrough


Why do keyboards with passthrough usb require two usb connections at the end of the cable instead of just one?

In: 4

Gotta make sure that the keyboard has enough power and also the hub has enough power. The worse case scenario is if usb 1.0 port is used. But, if you use a usb 2.0 or 3.0 or higher port, you might not actually need to plug both in.

The real answer is most keyboards with a usb passthrough isnt a passthrough at all, it’s just another usb cable run inside the main bundle with the other usb connection for the keyboard.

Few keyboards have an actual onboard usb hub, as that would cost more money and be harder to fit physically, so they just give you a spare usb port with a wire thats combined in the wrapped cable the original usb wire for the keyboard is running in.

Tl:dr it’s not an actual passthrough it’s a glorified usb extension cable basically, and because it’s cheaper that way.

A USB port provides a certain amount of power.

You could have one USB plug going to a USB hub chip in the keyboard, with the USB socket and the keyboard controller both connected to that hub chip.

But in that case, you need some power for the keyboard and the USB hub chip. So there is less power for the USB socket. For example, this might mean that you can plug in a flash drive but not a USB hard disk because the USB hard disk needs more power.

There are also issues with the many many optional features that USB can support. USB keyboards tend to use USB2 or even USB1 speeds, since they’re only sending a few key presses per second at most, and USB3 chips are more expensive. USB keyboards also don’t use fast charge for obvious reasons. But you might have USB ports on your PC that support those features, and you might want to plug in a device that uses those features.

So keyboard manufacturers build a simple dumb USB extension cable, with the socket built into the keyboard and all but the last few centimetres of the cable built into the keyboard’s USB cable.

That way, all the advanced features of your USB port just work. It is much simpler and cheaper and more reliable than trying to get a USB hub chip that supports all those features. There are also no power issues. It’s much more likely to work the way the end user expects, giving happier users and less support calls or returns.