Emotional Stress Indicator and Digital Thermometer-Project-8thsem
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This document outlines the contents and design of an emotional stress indicator and digital thermometer circuit. It includes sections on the introduction, methodology, circuit design, components used, operation of components, observations and conclusions for each project. The emotional stress indicator circuit measures changes in skin resistance to detect stress levels, while the digital thermometer circuit uses a temperature sensor and microcontroller to directly display temperature readings on an LED screen. Both circuits were successfully tested and achieved their objectives of measuring stress and temperature, respectively.
Emotional Stress Indicator and Digital Thermometer-Project-8thsem
- 1. CONTENTS I. EMOTIONAL STRESS INDICATOR 1. Introduction a) Definition of Galvanic Skin Response b) Methodology 2. Designing of circuit a) Circuit Diagram b) Layout diagram c) Components used and their specifications d) Function of each component e) Designing procedure 3. Observations 4. Conclusion II. DIGITAL THERMOMETER 1. Introduction a) Definition of Thermometer b) Advantages of Digital Thermometer c) Methodology 2. Designing of Circuit a) Circuit Diagram b) Layout Diagram c) Components used and their specifications d) Function of each component e) Designing procedure 3. Observations 4. Conclusion
- 2. I. EMOTIONAL STRESS INDICATOR INTRODUCTION This project is based on the concept of Galvanic Skin Response or commonly used acronym GSR. Galvanic Skin Response is a technique of measuring electrical conductance of skin, which varies with its moisture level. Moisture in skin refers to sweat produced by the sweat glands in our skin. This is of interest because the sweat glands are controlled by Sympathetic Nervous system, so skin conductance is used as an indication of physiological or psychological arousal. Human skin offers some resistance to current and voltage and this resistance changes with the emotional state of the human body. The project designed measures resistance changes 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, which reduces to 500 kilo-ohms or less when emotional stress is too high. The reduction in skin resistance is related to increased blood flow and permeability followed by the physiological changes during stress. This increases the electrical conductivity of the skin. The circuit used in this project is useful to monitor the skin’s response to relaxation techniques. It is highly sensitive and shows immediate response during a sudden change of stress.
- 3. Methodology The circuit uses a sensitive amplifier to sense variations in the skin’s resistance. IC CA3140 is designed as a resistance to voltage converter that outputs varying voltage based on skin’s conductivity. It is wired as an inverting amplifier to generate constant current to skin in order to measure the skin resistance. IC CA3140 is a 4.5MHz BiMOS operational amplifier with MOSFET (Metal Oxide Semiconductor Field Effect Transistor) inputs and bipolar outputs. The gate protected inputs have high impedance and can sense current as low as 10pA. Thus, this device is ideal 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 touch plates, while the non inverting input (pin3) is grounded directly. The output from the IC1 passes through current limiting resistor R1 to the second touch plate. R1 acts as a feed back along with the skin when the touch plates make contact with the skin. So the gain of 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 feedback network 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 varies depending on the current passing through the skin which in turn depends on skin response and emotional state. In the standby states, the touch plates are free as there is no feedback to IC1. It gives a high 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 output voltage reduces to 4volts or less depending on the resistance of the skin. Since the feedback network has a fixed resistor R1 and VR1 is fixed to a fixed value the current flowing through it depends only on the resistance of the skin. The output of IC1 is displayed on a sensitive moving coil meter (VU Meter). By varying VR2 one can control this 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 current from pin 18 to pin 10 will each increment of 125 mV at its input pin 5. Using VR3 one can 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 one finger between the touch plates. Maintain the finger still and allow one minute of bonding and keep the body relaxed. Adjust VR3 until the green LED lights up and meter shows full deflection. Adjust VR2 to get the maximum deflection of the meter. This indicates the normal resistance of the skin, provided the body is relaxed.
- 4. If the subject is stressed, the skin resistance decreases and the blue LED lights up followed by the red LED. DESIGNING OF CIRCUIT Circuit diagram:
- 6. Components used and their specifications: Component Specification Power Supply 9V, DC Resistor 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 pads LED Red, Green, Blue IC CA3140, LM3915
- 7. Function of each component 1) Power Supply Standard laboratory DC power supply equipment is used as a power source for this circuit. This circuit works on 9V DC supply. 2) Resistors A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. This relation is represented by Ohm's law: R=V/I Applications: >Resistors are common elements of electrical networks and electronic circuits and are ubiquitous 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) Potentiometer Potentiometer or commonly called Pots are variable resistors where resistance can be varied from zero to the maximum magnitude mentioned. 4) Touch pads Standard GSR touch pads are used which senses the electrical conductivity changes on the skin due to sweat variation at different stress levels. 5) Light Emitting Diodes They denote stress levels. Activated Green LED resembles relaxed state, Activated Blue LED denotes stressed condition and Activated Red LED denotes high stress condition.
- 8. 6) IC CA3140 The CA3140 is an integrated circuit operational amplifier that combines the advantages of high voltage PMOS transistors with high voltage bipolar transistors on a single monolith chip. Features a) Very high input impedance: 1.5T ohms b) Very low input current: 10 pA c) Wide common mode input voltage range d) Directly replaces industry available 741 in most applications Absolute 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
- 9. 7) LM3915 The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs, LCDs or vacuum fluorescent displays, providing a logarithmic 3 dB/step analog display. One pin changes the display from a bar graph to a moving dot display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The whole display system can operate from a single supply 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 of voltages Pinout diagram:
- 11. OBSERVATION: The Emotional Stress indicator device was tested on various human subjects and it delivered proper results. When subjects were emotionally calm and in relaxed state the Green LED flashed, while on stressed conditions blue LED flashed followed by Red LED. CONCLUSION: The project performed was successful. The objective to design an Emotional Stress Indicator was realized.
- 12. II. DIGITAL THERMOMETER INTRODUCTION A Thermometer is a device that measure temperature or temperature gradient. Any thermometer, be it digital or analog, has two basic elements. First, the temperature sensor, the conventional thermometers have mercury as the sensor, while the digital thermometers 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 a voltage as output, which can be measured using a voltmeter, or high end digital thermometers which are microcontroller enabled, display temperature directly on an LED panel. The sole advantages of using a digital thermometer are, firstly, they produce more accurate results than conventional thermometers, secondly, the digital thermometers can operate over a wide range of temperatures without any variations in its internal 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 full scale deflection Voltmeter or a multimeter as the output of this device is in volts.
- 13. Methodology: Operational Amplifier IC 741 (IC1) provides a constant flow of current through the base emitter junction of the n-p-n transistor BC108 (IC2). This BC108 is the sensor which senses temperature and generates corresponding voltage. The voltage across the base emitter junction of this transistor is proportional to its temperature. The transistor used in this way makes a very low cost sensor, thereby making the device cheap, yet useful. The small variation in the voltage across the base emitter junction is amplified by the second operational amplifier (IC4), before the temperature is displayed on the meter. Preset VR1 is used to set the zero reading on the meter and preset VR2 is used to set the range of 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 negative low dropout regulator IC 7660 (IC2). The entire circuit is driven by a 9V DC power supply. The thermometer can be calibrated using presets VR1 and VR2. After calibration the sensor should be placed at the vicinity of the object whose temperature is to be measured. The measured value is voltage, so for calibration purpose with respect to actual temperature, a standard conventional thermometer is taken. The object whose temperature is to be measured is first placed at the vicinity of the conventional thermometer, where the temperature is noted. Now this object is placed at the vicinity of the device which has been designed, i.e the digital thermometer. A voltage is generated which implies that for the corresponding temperature noted previously, the corresponding voltage is its corresponding electrical value. A set of readings is taken and this is how calibration process is completed. Measuring unknown temperatures now becomes easy for the device, because from the table constructed during calibration, the voltage generated by the device can be compared to the table where the temperature values are given. Thus the temperature of the unknown body gets measured.
- 14. DESINGING OF CIRCUIT a) Circuit diagram
- 16. c) Components used and their specifications Component Specification Power supply 9 V DC Resistor 10 k ohm, 10 k ohm, 100 k ohm. Capacitor Polar: 1 uF,16 V; 10 uF, 16V; 10 uF, 16V Non Polar: 220 nF Diode Zener diode. 4.7 V Potentiometer 100 k ohm, 500 k ohm Transistor BC108 Integrated circuit 7805, 7660, 741, 741
- 17. d) Functioning of each component 1) Power Supply Standard laboratory DC power supply equipment is used as a power source for this circuit. This circuit works on 9V DC supply. 2) Resistors A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. This relation is represented by Ohm's law: R=V/I Applications: >Resistors are common elements of electrical networks and electronic circuits and are ubiquitous 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) Potentiometer Potentiometer or commonly called Pots are variable resistors where resistance can be varied from zero to the maximum magnitude mentioned. 4) Capacitor A capacitor (formerly known as condenser) is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary 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 static electric field develops across the dielectric, causing positive charge to collect on one plate 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 the ratio of charge ±Q on each conductor to the voltage V between them: C=Q/V
- 18. Applications: Energy storage: >A capacitor can store electric energy when disconnected from its charging circuit, so it can 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 power applications. These include electromagnetic forming, Marx generators, pulsed lasers (especially TEA lasers), pulse forming networks, radar, fusion research, and particle accelerators. >Power conditioning: Reservoir capacitors are used in power supplies where they smooth the output of a full or half wave rectifier. >Signal processing: The energy stored in a capacitor can be used to represent information, either in binary 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 in particular frequency bands. For example, radio receivers rely on variable capacitors to tune the station frequency. Speakers use passive analog crossovers, and analog equalizers use capacitors to select different audio bands.