A pen drive is nothing but a USB flash memory stick, it has no power or other logic in it, it won't function on its own, you can find a recorder that uses USB flash memory, otherwise you will effectively have to build a self contained recorder that uses the flash drive.
Anything's "possible", but I think the word you're looking for is "feasible". Yes, it would be possible, but no, it wouldn't be feasible. It'd be a whole lot easier and cheaper to just buy a recorder. Like Smoothy said, you can get one with USB output that will allow you to save your lectures to your computer. I use one at work for quick notes, I think it only cost about $50 (US) but it's way better than trying to keep track of a pile of notes.
Go to eBay and search for "usb keychain digital voice recorder". Most look like they're from China so I don't know about the quality but the prices aren't too bad.
I wonder what else there is out there that I don't know about? I'm so far behind the times it's not even funny...
What you need, if you can afford it, is the Livescribe Echo, which is a pen with built-in recording facility:
http://reviews.cnet.com/voice-recorders/livescribe-echo-8gb/4505-11314_7-34142159.html
If you use special paper it also digitises your notes. If that is too much there are cheaper pens with a voice recording facility but without the digitising capability.
Yep, I went to eBay and searched for the Echo and they're all over the place, too! If I could justify the cost I'd put in a bid just to see if I could get one to play with. But you weren't kidding when you said "if you can afford it"!
Did i say i was going to buy one? Whatever for? While on my morning walk, i listen to music on my tiny Sony MP3 player....i remembered it has a recording facility. i tried it out...FM was superb, general mic recording using the internal mic was quite good if i pointed it at the source (not that great for surreptious recording i mean ). So i don't need one. Except as a gadget. i also realised that i have never needed to record anyone.......
Well sakthipriya, you are obviously a member of young India, and must be having an iPod or equivalent. It probably already has this facility. Otherwise eBay India also has stuff.
But those things are cute....
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