Re eeg, conductance, and respiratory rate:
Skin conductance: I assume you have a circuit already in mind to do this, wihich produces a voltage which is proportional to skin conductance. If so, I suggest you low-pass filter the signal (1 Hz cutoff probably fine, since this is a signal that doesn't change quickly). In general, lower conductance = sweatier skin = more activation of the sympathetic division of the autonomic nervous system.
EEG: never measured one. Conclusions about emotional state from EEG seems challenging at best to me, but I'm sure you have or will read up on this.
Respiratory rate:
Typically measured with a strain gage transducer in an elastic band placed around the chest. The strain gage is one arm of a Wheatstone bridge and a voltage is produced which is proportional to chest circumference. A peak-finding algorithm similar in concept to what you use for ECG can be used to find the number of peaks in a given time, and from that compute the respiratory rate.
Yes you will have to store some values of "normal" for each of th measured quantities. Those values can be settable by the user via front panel controls, or can be hard-wired as constants on the block diagram.
You will have to decide how to combine the results of the four measurements, and whether you want a binary or more graded type of "output". A binary output would be "excited" or "bored/relaxed" and could be done by soeme boolean logic: if 3 out of 4 measurements exceed some threshold, then the subject is excited. Use the elents on the boolean palette for this.
A physiologist would be skeptical about this entire enterprise (since the sympathtic and parasympathetic nervous systems are continually responding to a whole range of stimuli) , but it is still a nice student project if you don't take the results too seriously.
