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Simple and CHEAP voting system - AM? Answered

I'm a teacher, and I have a little (but not a lot) of money to spend. I'd really like to buy something like a Quizdom voting system, but with anything up to five classes of 26 running at once, it's just not financially possible. Which got me thunking...

AM radio transmitters are cheap to build right? I've seen one using a 555 timer and an NPN transistor - these cost pennies - use to transmit voice. Could I instead transmit a BEEP - or high tone or something - each timer on a slightly different frequency? And have a single receiver which then listens across this frequency range and identifies which frequency is transmitting the tone or signal and feeds that back into... PC, Arduino, Raspberry Pi? Range would only need to be like 5-10m.


Or, maybe pick up a job lot of cheap "universal" TV remotes, and an IR detector on the wall over your board - they can then "zap" their answer at your computer.

They may be more expensive than the radio transmitters you mentioned, but they will not interfere with other classrooms through the wall, and will save you many hours of work building the devices and enclosures that will stand up to abuse by pupils.