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

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?

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frollard6 years ago
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;
(3 bucks shipped)
(4 bucks shipped) can find them locally but they'll set you back 10-20 in a store.
*you may have used an adapter like this

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.
Martin 37 (author)  frollard6 years ago
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!

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.

what is the cost of it?

what is the cost of it?