A LIE DETECTOR

This project is about a lie detector and how it can respond to the physiological
reaction in human body. Basically there are three different systems which will reactto
the physiological changes. The first system use to sense the changes due to human
electrical skin resistance. As people are exposing to the stress situation, it is believe
that they will sweat more especially between fingers and palm. This will cause skin
resistance to become low than normal. Dry skin is said to have a resistance in Mega
Ohm while for the moist skin, the resistive value might be in the range of few Kilo
Ohm. Simple circuit act as a skin resistance sensor is implemented byusing a voltage
comparator. Based onthe physiological changes, heart rate will be faster than normal
when people are under stress and so do the blood pressure. According to the human
biological, normal heart rate is stated as 75 beats per minute (bpm) while blood
pressure is 120/80 mmHg. During the study, it is realized that both of the systems
(heart rate monitoring and blood pressure monitoring system) are possible to use the
same circuit for monitoring or even measuring purposes. This is because, variations in
both the heart rate and the blood cause expansion and contraction of the arteries and
veins throughout the body. So, the second system design is to detect both parameters
by using only one device. As the heart beat increases as well as the blood pressure,
the value for respiration rate also increases proportionally as we breathe faster
because there are more oxygen needed as the heart pumps the blood faster.