Emotional Stress Indicator and Digital Thermometer-Project-8thsem
CONTENTSI. EMOTIONAL STRESS INDICATOR1. Introductiona) Definition of Galvanic Skin Responseb) Methodology2. Designing of circuita) Circuit Diagramb) Layout diagramc) Components used and their specificationsd) Function of each componente) Designing procedure3. Observations4. ConclusionII. DIGITAL THERMOMETER1. Introductiona) Definition of Thermometerb) Advantages of Digital Thermometerc) Methodology2. Designing of Circuita) Circuit Diagramb) Layout Diagramc) Components used and their specificationsd) Function of each componente) Designing procedure3. Observations4. Conclusion
I. EMOTIONAL STRESS INDICATORINTRODUCTIONThis project is based on the concept of Galvanic Skin Response or commonly usedacronym GSR. Galvanic Skin Response is a technique of measuring electricalconductance of skin, which varies with its moisture level. Moisture in skin refers tosweat produced by the sweat glands in our skin. This is of interest because the sweatglands are controlled by Sympathetic Nervous system, so skin conductance is used as anindication of physiological or psychological arousal.Human skin offers some resistance to current and voltage and this resistance changeswith the emotional state of the human body. The project designed measures resistancechanges in human skin for changes in the mental/emotional state.In relaxed state, human skin offers resistance as high as 2 mega-ohms or more, whichreduces to 500 kilo-ohms or less when emotional stress is too high. The reduction in skinresistance is related to increased blood flow and permeability followed by thephysiological changes during stress. This increases the electrical conductivity of theskin.The circuit used in this project is useful to monitor the skin’s response to relaxationtechniques. It is highly sensitive and shows immediate response during a sudden changeof stress.
MethodologyThe circuit uses a sensitive amplifier to sense variations in the skin’s resistance. ICCA3140 is designed as a resistance to voltage converter that outputs varying voltagebased on skin’s conductivity. It is wired as an inverting amplifier to generate constantcurrent to skin in order to measure the skin resistance.IC CA3140 is a 4.5MHz BiMOS operational amplifier with MOSFET (Metal OxideSemiconductor Field Effect Transistor) inputs and bipolar outputs. The gate protectedinputs have high impedance and can sense current as low as 10pA. Thus, this device isideal to sense minute currents in low input current applications. The inverting input(pin2) of the above IC is connected to ground (through preset VR1) and one of the touchplates, while the non inverting input (pin3) is grounded directly. The output from the IC1passes through current limiting resistor R1 to the second touch plate. R1 acts as a feedback along with the skin when the touch plates make contact with the skin. So the gainof IC1 depends on the feedback provided by the skin and R1.In the inverting mode of IC1, a positive input voltage to its pin2 through the feedbacknetwork makes its output low. If the skin offers very high resistance in the relaxed state,input voltage to pin2 reduces and the output remains high. Thus the gain of IC1 variesdepending on the current passing through the skin which in turn depends on skinresponse and emotional state.In the standby states, the touch plates are free as there is no feedback to IC1. It gives ahigh output (around 6 volts) which is indicated by the meter shifting to the right side.When touch plates are shorted by the skin, the feedback circuit completes and outputvoltage reduces to 4volts or less depending on the resistance of the skin. Since thefeedback network has a fixed resistor R1 and VR1 is fixed to a fixed value the currentflowing through it depends only on the resistance of the skin. The output of IC1 isdisplayed on a sensitive moving coil meter (VU Meter). By varying VR2 one can controlthis meter.For visual observations an LED (Light Emitting Diode) display is included. IC LM3915(IC2) is used to give a logarithmic display through LED indications. It can sink currentfrom pin 18 to pin 10 will each increment of 125 mV at its input pin 5. Using VR3 onecan adjust the input voltage of IC2. VR4 is used to control the brightness of the LEDs.In practice, the circuit provides both meter reading as well as LED indications. Place onefinger between the touch plates. Maintain the finger still and allow one minute ofbonding and keep the body relaxed. Adjust VR3 until the green LED lights up and metershows full deflection. Adjust VR2 to get the maximum deflection of the meter. Thisindicates the normal resistance of the skin, provided the body is relaxed.
If the subject is stressed, the skin resistance decreases and the blue LED lights upfollowed by the red LED.DESIGNING OF CIRCUITCircuit diagram:
Components used and their specifications:Component SpecificationPower Supply 9V, DCResistor Carbon Resistor. 10 k ohm, 1 k ohm.Potentiometer 5k ohm, 5 k ohm, 50 k ohm, 100 k ohm.Touch pads Standard GSR touch padsLED Red, Green, BlueIC CA3140, LM3915
Function of each component1) Power SupplyStandard laboratory DC power supply equipment is used as a power source for thiscircuit. This circuit works on 9V DC supply.2) ResistorsA linear resistor is a linear, passive two-terminal electrical component that implementselectrical resistance as a circuit element. The current through a resistor is in directproportion to the voltage across the resistors terminals. This relation is represented byOhms law: R=V/IApplications:>Resistors are common elements of electrical networks and electronic circuits and areubiquitous in most electronic equipment.>Resistors are also implemented within integrated circuits, particularly analog devices,and can also be integrated into hybrid and printed circuits.3) PotentiometerPotentiometer or commonly called Pots are variable resistors where resistance can bevaried from zero to the maximum magnitude mentioned.4) Touch padsStandard GSR touch pads are used which senses the electrical conductivity changeson the skin due to sweat variation at different stress levels.5) Light Emitting DiodesThey denote stress levels. Activated Green LED resembles relaxed state, ActivatedBlue LED denotes stressed condition and Activated Red LED denotes high stresscondition.
6) IC CA3140The CA3140 is an integrated circuit operational amplifier that combines theadvantages of high voltage PMOS transistors with high voltage bipolar transistors on asingle monolith chip.Featuresa) Very high input impedance: 1.5T ohmsb) Very low input current: 10 pAc) Wide common mode input voltage ranged) Directly replaces industry available 741 in most applicationsAbsolute maximum ratings:> DC Supply Voltage (Between V+ and V- Terminals) . . . . . . . . . 36V> Differential Mode Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . 8V> DC Input Voltage . . . . . . . . . . . . . . . . . . . . . . (V+ +8V) To (V- -0.5V)> Input Terminal Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1mA> Output Short Circuit Duration ……….. . . . . . . . . . . . . . . Indefinite> Operating Conditions> Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . -55oC to 125oC
7) LM3915The LM3915 is a monolithic integrated circuit that senses analog voltage levels anddrives ten LEDs, LCDs or vacuum fluorescent displays, providing a logarithmic 3dB/step analog display. One pin changes the display from a bar graph to a moving dotdisplay. LED current drive is regulated and programmable, eliminating the need forcurrent limiting resistors. The whole display system can operate from a singlesupply as low as 3V or as high as 25V.Features:> 3 dB/step, 30 dB range> Drives LEDs, LCDs, or vacuum fluorescents> Bar or dot display mode externally selectable by user> Expandable to displays of 90 dB> Internal voltage reference from 1.2V to 12V> Operates with single supply of 3V to 25V> Inputs operate down to ground> Output current programmable from 1 mA to 30 mA> Input withstands ±35V without damage or false outputs> Outputs are current regulated, open collectors> Directly drives TTL or CMOS> The internal 10-step divider is floating and can be referenced to a wide range ofvoltagesPinout diagram:
OBSERVATION:The Emotional Stress indicator device was tested on various human subjects and itdelivered proper results. When subjects were emotionally calm and in relaxed state theGreen LED flashed, while on stressed conditions blue LED flashed followed by RedLED.CONCLUSION:The project performed was successful. The objective to design an Emotional StressIndicator was realized.
II. DIGITAL THERMOMETERINTRODUCTIONA Thermometer is a device that measure temperature or temperature gradient.Any thermometer, be it digital or analog, has two basic elements. First, the temperaturesensor, the conventional thermometers have mercury as the sensor, while the digitalthermometers have transistors, integrated circuits or electronic chips as sensors. Second,some means of converting this physical change into a numerical or measurable value.Conventional thermometers have a scale, while for digital thermometers we either get avoltage as output, which can be measured using a voltmeter, or high end digitalthermometers which are microcontroller enabled, display temperature directly on anLED panel.The sole advantages of using a digital thermometer are, firstly, they producemore accurate results than conventional thermometers, secondly, the digitalthermometers can operate over a wide range of temperatures without any variations in itsinternal configurations.The digital thermometer designed in this project measures temperatures upto 150°C with an accuracy of +/- 1°C. The temperature is measured indirectly using 1V fullscale deflection Voltmeter or a multimeter as the output of this device is in volts.
Methodology:Operational Amplifier IC 741 (IC1) provides a constant flow of current through the baseemitter junction of the n-p-n transistor BC108 (IC2). This BC108 is the sensor whichsenses temperature and generates corresponding voltage. The voltage across the baseemitter junction of this transistor is proportional to its temperature. The transistor used inthis way makes a very low cost sensor, thereby making the device cheap, yet useful. Thesmall variation in the voltage across the base emitter junction is amplified by the secondoperational amplifier (IC4), before the temperature is displayed on the meter. PresetVR1 is used to set the zero reading on the meter and preset VR2 is used to set the rangeof the temperature measurement.Operational amplifiers IC3 and IC4 operate off regulated +/- 5 V DC power supply,which is derived from 3 terminal positive voltage regulator IC 7805 (IC1) and negativelow dropout regulator IC 7660 (IC2). The entire circuit is driven by a 9V DC powersupply.The thermometer can be calibrated using presets VR1 and VR2. After calibration thesensor should be placed at the vicinity of the object whose temperature is to bemeasured. The measured value is voltage, so for calibration purpose with respect toactual temperature, a standard conventional thermometer is taken. The object whosetemperature is to be measured is first placed at the vicinity of the conventionalthermometer, where the temperature is noted. Now this object is placed at the vicinity ofthe device which has been designed, i.e the digital thermometer. A voltage is generatedwhich implies that for the corresponding temperature noted previously, thecorresponding voltage is its corresponding electrical value. A set of readings is taken andthis is how calibration process is completed.Measuring unknown temperatures now becomes easy for the device, because from thetable constructed during calibration, the voltage generated by the device can becompared to the table where the temperature values are given. Thus the temperature ofthe unknown body gets measured.
c) Components used and their specificationsComponent SpecificationPower supply 9 V DCResistor 10 k ohm, 10 k ohm, 100 k ohm.Capacitor Polar: 1 uF,16 V; 10 uF, 16V; 10 uF, 16VNon Polar: 220 nFDiode Zener diode. 4.7 VPotentiometer 100 k ohm, 500 k ohmTransistor BC108Integrated circuit 7805, 7660, 741, 741
d) Functioning of each component1) Power SupplyStandard laboratory DC power supply equipment is used as a power source for thiscircuit. This circuit works on 9V DC supply.2) ResistorsA linear resistor is a linear, passive two-terminal electrical component that implementselectrical resistance as a circuit element. The current through a resistor is in directproportion to the voltage across the resistors terminals. This relation is represented byOhms law: R=V/IApplications:>Resistors are common elements of electrical networks and electronic circuits and areubiquitous in most electronic equipment.>Resistors are also implemented within integrated circuits, particularly analog devices,and can also be integrated into hybrid and printed circuits.3) PotentiometerPotentiometer or commonly called Pots are variable resistors where resistance can bevaried from zero to the maximum magnitude mentioned.4) CapacitorA capacitor (formerly known as condenser) is a passive two-terminal electricalcomponent used to store energy in an electric field. The forms of practical capacitorsvary widely, but all contain at least two electrical conductors separated by a dielectric(insulator). When there is a potential difference (voltage) across the conductors, a staticelectric field develops across the dielectric, causing positive charge to collect on oneplate and negative charge on the other plate. Energy is stored in the electrostatic field.An ideal capacitor is wholly characterized by a constant capacitance C, defined as theratio of charge ±Q on each conductor to the voltage V between them:C=Q/V
Applications:Energy storage:>A capacitor can store electric energy when disconnected from its charging circuit, so itcan be used like a temporary battery.>Pulsed power and weapons:Groups of large, specially constructed, low-inductance high-voltage capacitors(capacitor banks) are used to supply huge pulses of current for many pulsed powerapplications. These include electromagnetic forming, Marx generators, pulsed lasers(especially TEA lasers), pulse forming networks, radar, fusion research, and particleaccelerators.>Power conditioning:Reservoir capacitors are used in power supplies where they smooth the output of a fullor half wave rectifier.>Signal processing:The energy stored in a capacitor can be used to represent information, either inbinary form, as in DRAMs, or in analogue form, as in analog sampled filters and CCDs.>Tuned circuits:Capacitors and inductors are applied together in tuned circuits to select information inparticular frequency bands. For example, radio receivers rely on variable capacitors totune the station frequency. Speakers use passive analog crossovers, and analogequalizers use capacitors to select different audio bands.