As your name suggested someone who is trying to invent things I’ve got an idea I’d like to share with you:
http://www.gliffy.com/publish/1341973/

I am a teacher and I’d like my students to all have their own infrared device that sends my computer a signal. Should I focus on the software side or the hardware side in this invention?

Any thoughts on this matter are very welcome.

Any advice I could give would depend a lot on your background. If you’re comfortable creating embedded circuits, this would be a manageable project. There was an article in the Jan 08 issue of Circuit Cellar Mag. about creating a device that could record and play back remote control signals, ie, a learning universal remote. The main components of the circuit included a microcontroller and IR receiver and transmitter. Lots of PICs come with built in USB functionality that would let you talk to code on a PC. This is most definitely not a beginner project, but very do able if you have some experience.

If you don’t have experience, another route might be to write code for the original Lego RCX. It connects to a PC via USB and talks to the main microcontroller brick via infrared. You might be able to hack that device and get it to send strings from random remote controls to the PC.

That’s my two cents.

That’s a cool idea. I think it might be possible to use relatively cheap learning remote controls to do this. The Sony RM VL600 is probably not the cheapest, but just an example.

To program a unique code into each remote, the computer software could send out an IR code while you hold a remote in front of an IR emitter connected to the computer. Program each button on each remote with a unique code.

Some potential issues I can anticipate: TV remotes are modulated on a carrier frequency of something around 40kHz. This frequency may not be compatible with your computer’s IRDA port. Luckily there are products available to interface your computer with TV remotes. (try TV-Tuner cards)

Another potential problem is collisions between signals from multiple remotes being pressed at the same time. Commercial systems probably use higher data rates (for shorter duration signals) and other collision prevention methods. In a class of 4 students this probably wouldn’t be that big of a problem (especially if students can verify that their answer was received), but in a class that small you probably won’t need this system anyway.
Perhaps you could have a screen that highlights each student’s name sequentially and that student can submit his answer while his name is highlighted to avoid the collision issue.

The “PRS” system we used at my school was not always responsive to key presses. Sometime I had to press several times and verify that my response showed up on the screen. Their old system used IR transmitters, but has upgraded to newer (even more expensive) RF based models since then.