Is it possible? PS/2 to USB connector?! - Page 1
Forum section: electronics / beginners

author: ali6x944
author_rank: Frequent Contributor
timestamp: May 20, 2016, 05:44:15 pm
content: Hi everyone,I had a old keyboard laying around which have a PS/2 connector on it but my laptop doesn't have PS/2 connector so I ask Is it possible? PS/2 to USB connector?! Directly?

author: coppice
author_rank: Super Contributor
timestamp: May 20, 2016, 05:48:18 pm
content: You can buy adaptors. The ones I have used have one USB connector and two PS/2 connectors - one for a PS/2 mouse and one for a PS/2 keyboard.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 20, 2016, 05:49:36 pm
content: https://www.adafruit.com/products/971

author: ali6x944
author_rank: Frequent Contributor
timestamp: May 20, 2016, 06:05:50 pm
content: Using this method:

author: Monkeh
author_rank: Super Contributor
timestamp: May 20, 2016, 06:07:52 pm
content: Quote from: ali6x944 on May 20, 2016, 06:05:50 pmNo.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: May 20, 2016, 06:14:39 pm
content: I've purchased devices similar to the one posted by Richard Crowley many times, they work just fine.

author: ali6x944
author_rank: Frequent Contributor
timestamp: May 20, 2016, 06:26:08 pm
content: Quote from: Monkeh on May 20, 2016, 06:07:52 pmQuote from: suicidaleggroll on May 20, 2016, 06:14:39 pmWhat so will it work or not?

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 20, 2016, 06:37:04 pm
content: The protocol used by the old PS2 keyboard/mouse is NOT the same as USB.You cannot connect them straight across like that.What we call the "PS2 protocol" is actually I2C. NOT compatible with USB.Some modern USB keyboards have auto-sense and will work with a simple converter.But it would be extraordinary to find an old PS2/I2C keyboard that would speak USB.Especially since USB hadn't even been invented yet.I strongly suspect there is a tiny protocol conversion chip in the USB plug that does the conversion.

author: electr_peter
author_rank: Unknown
timestamp: May 20, 2016, 06:43:11 pm
content: Some mouse/keyboard devices support both PS/2 and USB on the same lines, thus making simple passive adapters (USB<->PS2) possible. Other devices require special active PS2<->USB converters.One can always try to see if it works. PS2 is ancient, are you sure you really need it?

author: wraper
author_rank: Unknown
timestamp: May 20, 2016, 06:43:16 pm
content: Quote from: ali6x944 on May 20, 2016, 06:26:08 pmIf this keyboard is less than 10 years old, quiet likely it will. The older is the keyboard, the less chance you have it working.

author: Monkeh
author_rank: Super Contributor
timestamp: May 20, 2016, 07:00:39 pm
content: Quote from: ali6x944 on May 20, 2016, 06:26:08 pmWiring a PS/2 keyboard to a USB port is entirely different to using an active adapter.You cannot wire a PS/2 keyboard to a USB port. You can wiresomeUSB keyboards to PS/2 ports.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: May 20, 2016, 07:48:46 pm
content: Quote from: ali6x944 on May 20, 2016, 06:26:08 pmWill what work? I highly doubt the wiring schematic you posted would work at all, I wasn't talking about that. The adapter posted by Richard Crowley does not just map pins, it does the full USB to PS/2 translation and works just fine.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: May 20, 2016, 07:51:56 pm
content: Quote from: Richard Crowley on May 20, 2016, 06:37:04 pmYes there absolutely is, it says so on the page you linked to:Quote

author: wraper
author_rank: Unknown
timestamp: May 20, 2016, 09:52:15 pm
content: Quote from: Monkeh on May 20, 2016, 07:00:39 pmYes you can, manufacturers often use the same chipset and only connector is different.Quotemost of them

author: Monkeh
author_rank: Super Contributor
timestamp: May 20, 2016, 10:05:11 pm
content: Quote from: wraper on May 20, 2016, 09:52:15 pmOf the few dozen I have on hand? Maybe two or three USB ones which are definitely compatible (came with the adapter), most which are not, and a few PS/2 ones which mostly predate USB acceptance. So.. I disagree.

author: ali6x944
author_rank: Frequent Contributor
timestamp: May 21, 2016, 07:19:55 am
content: So I have to use a microcontroller of some kind to to connect from ps/2 to usb...

author: Monkeh
author_rank: Super Contributor
timestamp: May 21, 2016, 11:06:31 am
content: Quote from: ali6x944 on May 21, 2016, 07:19:55 amOr just buy the off-the-shelf adapter.

author: ali6x944
author_rank: Frequent Contributor
timestamp: May 21, 2016, 11:40:00 am
content: PS/2 pulgs uses I²C right?

author: rsjsouza
author_rank: Super Contributor
timestamp: May 21, 2016, 11:48:45 am
content: Quote from: Monkeh on May 21, 2016, 11:06:31 amAs others have said, an old PS/2 keyboard will not work if connected directly to a USB port such asthis one- some more modern keyboards and mice would have the USB/PS/2 auto-sense circuitry mentioned.You need an active microcontroller-based converter but several adapters will have some trouble with a 104-key ABNT2 keyboard - in my experience most of the keys will work but not the backslash and the period in the numeric keypad.One adapter I use withmy ABNT2 Model M keyboardisthis one- all keys but the period on the keypad work. Make sure you get the version 2.0 of that.

author: Ian.M
author_rank: Super Contributor
timestamp: May 21, 2016, 12:47:42 pm
content: PS/2 uses 5V signalling over a two wire open collector bus. The clock is generated by the device but can be inhibited by the host. the data line is bidirectional. This is totally different from USB which uses 3.3V quasi-differential signalling.Some keyboard and mouse chipsets during the transition period (round about the turn of the Millennium) when Microsoft & Intel were pushing the 'Legacy free PC' could do both, and detect what type of port they were connected to (quite easy - if pulled up to 5V talk PS/2 otherwise activate their USB SIE and gate it onto the bus), via a proprietary 'dumb' adapter.I wouldn't expect most modern keyboards to support both protocols, and old ones from the early days of USB didn't either. I seem to remember a lot of Logitech Keyboards/Mice from that era that supported both, but their adapters were usually not interchangable with other brands. You'd need to check the user manual of the specific model device you have to see if there's any chance that a dumb adapter will work, then will have to get lucky and find an adapter with the correct (almost invariably undocumented) wiring for your device.Dual interface mode keyboards and mice are nowadays only a historical curiosity. You'd be far better off getting a budget USB keyboard or if you have a really nice legacy IBM or Cherry mechanical PS/2 keyboard, getting a smart USB <=> dual port Keyboard/Mouse adapter.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 21, 2016, 01:31:39 pm
content: Quote from: ali6x944 on May 21, 2016, 11:40:00 amCorrect

author: Ian.M
author_rank: Super Contributor
timestamp: May 21, 2016, 01:40:02 pm
content: Quote from: Richard Crowley on May 21, 2016, 01:31:39 pmWRONG! Its nothing like I2C apart from the open collector bus. A few of the differences are no addressing, different framing and ACK.Seehttp://computer-engineering.org/ps2protocol/Just about the only place you'll find an external I2C interface on an ordinary PC is the DDC2B bus on its VGA or DVI monitor port.

author: Brumby
author_rank: Unknown
timestamp: May 21, 2016, 02:08:05 pm
content: Just use an off-the-shelf adapter.I've used three different models (from China) on keyboards and barcode scanners without any problem. For the price, you wouldn't bother messing about.

author: ali6x944
author_rank: Frequent Contributor
timestamp: May 21, 2016, 05:46:06 pm
content: Thanx everyone I will do what u suggested guys,Thanx very much.

author: Raj
author_rank: Frequent Contributor
timestamp: May 22, 2016, 02:49:47 pm
content: Here-https://www.youtube.com/watch?v=UJaqHnPR-XEKinda overkill, you'll need Bluetooth dongle

author: lapm
author_rank: Frequent Contributor
timestamp: May 22, 2016, 04:13:16 pm
content: I would go with off the self adapter. Saves you from many headaches...

author: rch
author_rank: Regular Contributor
timestamp: May 23, 2016, 10:39:24 am
content: I would just mention my experience with a " NEWLink USB to PS/2 Keyboard & Mouse Cable". It basically didn't work, but some random keyboard our mouse messages got through and unexpected things happened.On the other hand I have had excellent experience with very old ps/2 mice and keyboards and a Belkin adaptor to USB. They don't seem to sell them any more, though.