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How to connect a PS/2 keyboard to a USB port? Answered

I have a Logitech 250 keyboard with a PS/2 connector and would like to connect it to a USB port on my laptop. I bought a keyboard PS/2 to USB adapter, but it did not work. So, I bought a combined keyboard/mouse PS/2 to USB adpater and this did work. I no longer have it and it was quite bulky. So, I bought a USB plug, cut the PS/2 connector off the cable and carefully soldered the USB plug in its place. I checked the colour coding of the wires inside the keyboard: Vcc + is red, Data 1 is yellow, Data 2 is green, 0 v is white and Screen is black. I looked up the USB pin outs on Wikipedia and made sure that the Vcc and O v wires were in the correct positions on the USB plug by carefully metering the pins on the laptop USB port. I tried connecting the yellow wire to pin 2 and green wire to pin 3 on the USB plug and the reverse, but neither worked. Logitech support offered me a discount on a USB keyboard, but I'm intrigued to know why it does not work, when the combined keyboard/mouse PS/2 to USB adpater did work. Can anyone enlighten me and hopefully tell me how to make it work?

Tags:PS2 USB

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frollardBest Answer (author)2011-10-08

Most usb keyboards are ps/2 compatible -- they can just detect when you use an adapter and start 'talking' ps/2 protocol instead of usb over the same wires.

ps/2 Keyboards often don't do the same, they only operate on ps/2. They are not protocol, wire, or plug compatible with usb. HENCE why you needed that bulky ps/2 usb adapter.

Adapters can be had for cheap; http://www.dealextreme.com/p/slim-usb-2-0-to-ps-2-adapter-dongle-1440
(3 bucks shipped)

http://www.dealextreme.com/p/usb-to-ps-2-cable-adapter-15cm-length-45594
(4 bucks shipped)

...you can find them locally but they'll set you back 10-20 in a store.

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frollard (author)frollard2011-10-08

*you may have used an adapter like this http://www.dealextreme.com/p/ps2-to-usb-adapter-744

and if it didn't work, then it proves the keyboard isn't usb compatible - no amount of soldering will fix that... just gotta rewire that plug and get an active dongle.

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Martin 37 (author)frollard2011-10-09

Thanks very much. The adapter that did work was similar to usb-to-ps-2-cable-adapter-15cm-length-45594 and the one that did not work was like ps2-to-usb-adapter-744. So, as you say, the answer is that the combined adapter has an active component in it. I'll buy another as you suggest and do a bit more soldering!

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illumation_ (author)2016-07-23

Hmmm, got a logitech keyboard here with chopped off connector and red seems to be +5V and yellow is GND. The other two green and white are data wires and there is also a blank cable.

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gopakumar.gk.52 (author)2015-02-18
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gopakumar.gk.52 (author)2015-02-18