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Re: [school-discuss] Open Source Classroom Response Software "clickers"
So, do all receivers (once they decode the signal)
return the same 'code' for a particular transmitter?
(pardon my ignorance)
Yes, it is a simple binary number.
As well, how does one set particular transmitters to be
unique? (ie. identify themselves)
That is what makes universal remotes so usefull in this
type of application. Each device has its own ID code,
which allows the TV and VCR to use the same remote because
they listen for their ID before accepting a command. A
cheap universal remote will have hundreds of different
device ID's programmed in. The device ID's become the
student ID's, and the commands become the different
possible responses.
I assume that we want individual transmitters sending
sending a code (ie. we can then record each transmitter's
input (ie. it's ID code of some sort and Response Code of
another sort).
Correct?
Yes, there are 4 or 5 different encoding schemes on a
typical universal remote. Most are very similar. For
instance, sony devices use a 5 bit ID followed by a 7 bit
command. The number buttons on the remote generally send a
simple binary equivalent as a series of short and long
bursts of IR(like morse code). Most other encoding schemes
are similar in structure, but the length of a short or
long burst may be different for a phillips code. Also some
encoding schemes use a 7 bit ID instead of 5 bit. So when
you program a universal remote to work with your VCR you
are really just picking the encoding scheme for the
manufacturer and the device ID to match your device. For
the sony codes there are 32 different IDs, so just using
those you could nearly run a whole class with a single
decoding algorithm. Add in a couple more encoding schemes
and you could scale all the way up to large college
lecture classes.
For a good explanation of the most common encoding schemes
see <http://users.telenet.be/davshomepage/>