Stress Meter Project Report 674l4j

1

ABSTRACT

Stress is a term that refers to the sum of the physical, mental, and emotional strains or tensions on a person. Feelings of stress in humans result from interactions between persons and their environment that are perceived as straining or exceeding their adaptive capacities and threatening their well-being. The element of perception indicates that human stress responses reflect differences in personality as well as differences in physical strength or health. This Stress meter allows to assess one’s emotional pain. If the stress is very high, it gives visual indication through LED display along with a warning yellow light.

Stress meter is based on the principle that the resistance of the skin varies in accordance with your emotional states. Resistance varies inversely proportional to the stress. If the stress level is high the skin offers less resistance, and if relaxed, resistance is high.

In an article “Stress and Mind Control”, 21/03/2008, Roberto Bonomi stated that “When we speak of the fabulous relaxation capacity that mind control gives us, the first thing that comes to our mind, is that we will be able to take off, the excesses of nervous tension, the stress; and this is a great benefit. Because suppose that you could measure stress in inches, and that you have stress zero when the meter is located in zero.” Based on this our project is aimed to give a visual indication of one’s stress through a light-emitting diode display along with a warning light.

2

LIST OF TABLES

1. Table 3.1: LED Color Vs. Potential difference…………………...13 2. Table 4.1: LED Vs. Threshold voltage…………………………...19

3

LIST OF FIGURES

1) Fig 2.1: Block diagram of stress meter………………………….… .. 6 2) Fig 3.1: Dot/Bar display driver……………………………….…. ..... 8 3) Fig 3.2: The piezo element ……………………………………….… .9 4) Fig 3.3: Piezo electric diaphragm……………………………….…. ..10 5) Fig 3.4: Touch pad……………………………………………..…… .10 6) Fig 3.5: Light emitting diode……………………………………… ...11 7) Fig 3.6: Inside a light emitting diode………………………………. ..12 8) Fig 3.7: Regulated power supply……………………………….….. ..14 9) Fig 3.8: Voltage regulator…………………………………………… 14 10) Fig 3.9: Circuit diagram of Stress meter……………………………. .15 11) Fig 4.1: Basic block diagram showing the operation of the circuit… .17 12) Fig 4.2: Role played by touch pads…………………………………. 18 13) Fig 4.3: Bridge Rectifier Circuit…………………………………….. 20 14) Fig 4.4: The Power supply generation………………………………..21

4

Chapter 1 INTRODUCTION

1.1 STRESS METER Stress is the very common condition of every human being. Stress is nothing more than a socially acceptable form of mental illness. This Stress meter allows to assess the emotional pain. If the stress is very high, it gives visual indication on a LED display along with a warning light. Stress meter is based on the principle that the resistance of the skin varies in accordance with your emotional states. Resistance varies inversely proportional to the stress. If the stress level is high the skin offers less resistance, and if relaxed resistance is high. The low resistance of the skin during high stress is due to an increase in the blood supply to the skin. This increases the permeability of the skin and hence the conductivity for electric current. This property of the skin is used here to measure the stress level. Using suitable circuitry we can convert the amount of stress a human being feels to a varying analog voltage. The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LED’s, LCD’s or vacuum fluorescent displays, providing a logarithmic 3dB/step analog display. The touch pads of the stress meter sense the voltage variations across the touch pads and convey the same to the circuit. The circuit is very sensitive and detects even a minute voltage variation across the touch pad.

5

1.2 EVOLUTION In an article “Stress and Mind Control”, 21/03/2008, Roberto Bonomi stated that “When we speak of the fabulous relaxation capacity that mind control gives us, the first thing that comes to our mind, is that we will be able to take off, the excesses of nervous tension, the stress; and this is a great benefit. Because suppose that you could measure stress in inches, and that you have stress zero when the meter is located in zero.” Based on this, our project is aimed to give a visual indication of one’s stress through a light-emitting diode display along with a warning yellow light.

1.3 PURPOSE OF THE PROJECT The purpose of stress meter is to assess the emotional pain of human being. The stress can cause hair to fall, acne to break out and many other problems. These manifestations of stress can cause even more anxiety. Stress causes cortical levels to increase within the body, which increases oil production, which causes acne breakouts. So this stress meter is to solve all the problems caused due to stress by checking the stress of an individual and taking care before any serious problem occurs.

6

Chapter 2 BLOCK DIAGRAM AND PROJECT OVERVIEW

2.1 PRINCIPLE OF STRESS METER: The stress meter is based on the principle that the variations in the resistance of the skin due to blood pressure of ones’ body can be directly converted and transmitted into analog voltage levels to give the visual indication of human stress using a proper circuitry.

2.2 BLOCK DIAGRAM:

230 volts AC power Supply

Input through Touch Pads

Regulated Transformer

power supply

Dot/Bar Display Driver

Out Put Stress Lev Indication

High Stre Indicatio

7 Fig: 2.1 Block diagram of stress meter

2.3 BLOCK DIAGRAM DESCRIPTION: The 230 volts ac power supply is given to the transformer. The transformer steps down the input voltage line and isolates the power supply from the power line. A full wave bridge rectifier circuit along with a voltage regulator is used to give a regulated power supply to the circuit .The input touch pads are used to sense the resistance of our skin and this input is fed to the dot/bar display driver. The dot/bar display driver accepts the input through the touch pads which sense the small change in resistance the dot/bar driver gives the output stress level indication according the input. The output is indicated on a led display .The ten led’s act like the stress level indicators form zero stress level to high stress level on a scale of ten. The high stress detected from the dot/ bar display driver is indicated through a warning yellow light.

2.4 APPLICATION: Each LED in stress meter operates with a 3dB difference from the previous one, and a jumper is provided to allow dot or bar mode. This project is an essential part of the expandable analyzer and one meter circuit is used for each frequency band. There are many other uses for a simple LED meter. They are ideal as power meters on amplifiers, can be used with mixers (including the high quality mixer), preamps and any other application where it is important to know the signal level.

8 LM3915's 3 dB/step display is suited for signals with wide dynamic range, such as audio level, power, light intensity or vibration. Audio applications include average or peak level indicators, power meters and RF signal strength meters. Replacing conventional meters with an LED bar graph results in a faster responding, more rugged display with high visibility that retains the ease of interpretation of an analog display.

Chapter 3 COMPONENTS OVERVIEW

3.1 DOT/BAR DISPLAY DRIVER: 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.

LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of ±35V. The input buffer drives 10 individual

9 comparators referenced to the precision divider. Accuracy is typically better than 1 dB.

Fig: 3.1 Dot/Bar display driver

3.2 THE PIEZO ELEMENT: Piezoelectric diaphragm is a basic electronic sound component. It has the advantages of simple structure, stable performance and high reliability. It is not only the core element of piezoelectric buzzers and the alarms, but also used as shock sensors in many sensitive equipments.

10

Fig 3.2 The piezo element

Basically, the sound source of a piezoelectric sound component is a piezoelectric diaphragm. A piezoelectric diaphragm consists of a piezoelectric ceramic plate which has electrodes on both sides and a metal plate (brass or stainless steel, etc.). A piezoelectric ceramic plate is attached to a metal plate with adhesives. Applying D.C. voltage between electrodes of a piezoelectric diaphragm causes mechanical distortion due to the piezoelectric effect

Design Considerations: These devices contain no electronics, and require external circuitry to produce an audible tone. Presence of the tab enables the designer to simplify the drive circuit. Voltage applied to the device produces mechanical

11 distortions which are usable, among other applications, in alarms and sensors.

Fig 3.3 Piezo electric diaphragm The Touch Pad: The Touch Pad is two tinned pads on the PC board. When touched them with a finger, the resistance of the finger is reduced by a factor of about 100 - 400 by the gain of the emitter-follower transistor and this puts a HIGH on the input pin of the chip. The input impedance of the chip is fairly high (about 50k) but when you add a pull-down resistor (to prevent stray signals being detected by the chip), the impedance decreases. The answer is to add the emitter-follower transistor.

Fig: 3.4 Touch pad

12

3.3 LIGHT EMITTING DIODES: A light emitting diode (LED) is a PN junction semiconductor diode that emits photons when electrical current es through the junction in the forward direction, the electrical carriers give up energy proportional to the forward voltage drop across the diode junction, this energy is emitted in the form of light.

Fig 3.5 Light Emitting Diode LED’s are used in numerical displays such as those on electronic digital watches and pocket calculators. By definition, it is a solid-state device that controls current without heated filaments and is therefore very reliable. LED’s are highly monochromatic, emitting a pure color in a narrow frequency range. The color emitted from an LED is identified by peak wavelength and measured in nanometers. LEDs are made from gallium-based crystals that contain one or more additional materials such as phosphorous to produce a distinct color. LED light output varies with the type of chip, encapsulation, efficiency of

13 individual wafer lots and other variables. Several LED manufacturers use such as "super-bright," and "ultrabright" to describe LED intensity.

Because LED’s are solid-state devices they are not subject to catastrophic failure when operated within design parameters. LED’s are current-driven devices, not voltage driven. Although drive current and light output are directly related, exceeding the maximum current rating will produce excessive heat within the LED chip due to excessive power dissipation. The color of an LED is determined by the semiconductor material, not by the coloring of the 'package' (the plastic body). LEDs are available in red, orange, amber, yellow, green, and blue and white colors. LED’s are specially constructed to release a large number of photons outward. Additionally, they are housed in a plastic bulb that concentrates the light in a particular direction

Fig 3.6 Inside a Light Emitting Diode

14 Design Parameters: Never an LED should be connected directly to a battery or power supply. It will be destroyed almost instantly because too much current will through and burn it out. An LED must have a resistor connected in series to limit the current through the LED; otherwise it will burn out almost instantly and try to avoid connecting them in parallel.

LED Color

Potential Difference

Infrared red orange yellow green blue white ultraviolet

1.6V 1.8 to 2.1V 2.2V 2.4V 2.6V 3.0V to 3.5V 3.0V to 3.5V 3.5V

Table 3.1 LED color vs. potential difference Equation to determine the required resistance: Resistance = (Source Voltage – LED Voltage Drop) / desired current To drive an LED from a system, the following values are used: Source voltage = 13.4 volts (approximately) Voltage drop = 3.6 volts (typical for a blue or white LED) Desired current = 30 milliamps (typical value)

15 So the resistor we need is: (13.4 – 3.6) / (30 / 1000) = 327 ohms (Approximately 330 ohms).

3.4 REGULATED POWER SUPPLY: In a typical linear power supply, AC line voltage is first down-converted to a smaller peak voltage using a transformer which is then rectified using a full wave bridge rectifier circuit. A capacitor filter is then used to smoothen the obtained sinusoidal signal. The residual periodic variation or ripple in this filtered signal is eliminated using an active regulator.

Fig: 3.7 Regulated power supply To obtain a DC power supply with both positive and negative output voltages, a center-tapped transformer is used, where a third wire is attached to the middle of the secondary winding and it is taken as the common ground point. Then voltages from the opposite ends of the winding will be positive or negative with respect to this point

16 Care should be taken while connecting 78XX and 79XX ICs. Voltage Regulator: The 7805 takes in a voltage between 7 and 30 volts and regulates it down to exactly 5 volts. The first capacitor takes out any ripple coming from the transformer so that the 7805 is receiving a smooth input voltage, and the second capacitor acts as a load balancer to ensure consistent output from the 7805.

The 7805 has three leads. If the 7805 is seen from the front (the side with printing on it), the three leads are, from left to right, input voltage (7 to 30 volts), ground, and output voltage (5 volts).

Fig 3.8 Voltage regulator

3.5 CIRCUIT DIAGRAM OF STRESS METER:

17

Fig 3.9 Circuit diagram of Stress meter

Chapter 4

18

CIRCUIT OPERATION 4.1 OPERATION OF THE CIRCUIT: This stress meter circuit uses just one IC and a very few number of external components. It displays the input level in of 10 LEDs. The suggested input voltage can vary from 12V to 20V. The LM3915 IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of 35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 1 dB. A high input impedance buffer operates with signals from ground to 12V, and is protected against reverse and over voltage signals. The signal is then applied to a series of 10 comparators; each of which is biased to a different comparison level by the resistor string. The LM3915 is extremely easy to apply. A 1.2V fullscale meter requires only one resistor in addition to the ten LEDs. One more resistor programs the full-scale anywhere from 1.2V to 12V independent of supply voltage. LED brightness is easily controlled with a single pot. The following relations can be used to know the approximate values of current and reference voltages. V ref = 1.25 (1+R2/R1) + R2* 80UA I (LED) = (12.5V/R1) + (Vref/2.2K)

19 The outputs can drive LCDs, vacuum fluorescents and incandescent bulbs as well as LED’s of any color. Multiple devices can be cascaded for a dot or bar mode display with a range of 60 or 90 dB. LM3915s can also be cascaded with LM3914s for a linear/log display or with LM3916s for an extended-range VU meter. 4.2 CIRCUIT CONNECTIONS: The pins 2, 4 and 8 of the LM3915 are grounded. 6 and 7 pins are shorted and a resistor is connected across them which is grounded. Pin 1 and pins 10 to 18 are connected to LED’s to be driven by the IC. Pin 9 and 11 are shorted to give a bar mode display.3 pin is given the input voltage. Pin 5 is used to connect the touch pads.

20

Fig 4.1 Basic block diagram showing the operation of the circuit

4.3 ROLE PLAYED BY TOUCH PADS: The touch pad which is a piezoelectric substance senses the skin resistance when touched with a finger and acts like the

21 input to the circuit. The output stress level is indicated on the LED display. The high stress level is indicated by a warning yellow light. The following figure gives a clear idea of the principle behind the stress meter and the role played by the touch pads.

Conducting pad (upper)

Conducting pad (lower)

Top view

Fig 4.2 Role played by touch pads

4.4 THE LED DISPLAY:

Resistance between the pads varies based on wetness and dryness of the skin of the finger Insulator strip (between the upper and lower pad)

Side View sis

22 The output is indicated on a LED display .The ten LED’s act like the stress level indicators form zero stress level to high stress level on a scale of ten. The high stress detected from the dot/ bar display driver is indicated by a yellow light.

LED

THRESHOLD

1 2 3 4 5 6 7 8 9 10

60mV 80mV 110mV 160mV 220mV 320mV 440mV 630mV 890mV 1.25V

Table 4.1 LED Vs. Threshold voltage

4.5 POWER SUPPLY GENERATION: The 230 volts ac power supply is fed to the transformer and the transformer in turn is connected to a bridge rectifier circuit. When four diodes are connected as shown in figure, the circuit is called a BRIDGE RECTIFIER. The input to the

23 circuit is applied to the diagonally opposite corners of the network, and the output is taken from the remaining two corners. On the positive half cycle of transformer secondary supply voltage, diodes D1 and D2 conduct, supplying this voltage to the load. On the negative half cycle of supply voltage, diodes D3 and D4 conduct supplying this voltage to the load. It can be seen from the waveforms that the peak inverse voltage of the diodes is only Vm .The average output voltage is the same as that for the center-tapped transformer full-wave rectifier. With a resistive load, the load current is identical in shape to the output voltage. Most loads are inductive and the load current with these loads depends on the value of load resistance and load inductance so they do not conduct any current.

24

Fig 4.3 Bridge Rectifier Circuit During the negative half-cycle, the top end of the transformer winding is negative. Now, D1 and D4 are forward biased, and D2 and D3 are reverse biased. Therefore, electrons move through D1, the resistor, and D4 in the direction shown by the blue arrows. As with the positive half-cycle, electrons move through the resistor from left to right. In this manner, the diodes keep switching the transformer connections to the resistor so that current always flows in only one direction through the resistor. The resistors can be replaced with any other circuit, including more power supply circuitry (such as the filter), and still see the same behavior from the bridge rectifier.

Fig 4.4 The Power supply generation

25

The output from the bridge rectifier is thus connected to voltage regulator 7805 to generate 5 volts regulated power supply to the circuit. The capacitors are used as filters to smoothen the sinusoidal signals.

4.6 THE STRESS METER:

26

Chapter 5 RESULTS AND ANALYSIS

27 5.1 RESULTS: The stress meter thus detects the resistance of skin which is according to one’s mental stress and gives a visual indication on a LED display. The LED’s on the stress meter can be observed as stress level indicators form zero to ten stress levels on a scale of ten. The high stress of a person is indicated through a warning yellow light.

5.2 ANALYSIS: Resistance varies inverse proportional to the stress. If the stress level is high the skin offers less resistance, and if relaxed resistance is high. The low resistance of the skin during high stress is due to an increase in the blood supply to the skin. This increases the permeability of the skin and hence the conductivity for electric current. The LED 1 glows by default when the circuit is on. When a person touches the touch pad of the stress meter with his finger, it senses the skin resistance and hence the stress. On a scale of ten, stress levels from 0 to 10 can be observed, where the LED 10 when on gives a warning yellow light high stress indication.

28

Chapter 6 CONCLUSION

6.1 SUMMARY: In this project, is proposed a stress meter that indicates the stress level of a human being based on one’s skin resistance on a scale of ten. The circuit uses the IC LM3915 which is a dot/bar display driver which can easily drive ten led’s with a suggested input voltage. The touch pad which is a piezoelectric substance senses the skin resistance when touched with a finger and acts like the input to the circuit. The output stress level is indicated on the led display. The high stress level is indicated by a warning yellow light. The regulated power supply used in the project gives an input voltage of 5V for the circuit to operate. A switch is used to ON/OFF the circuit.

6.2 APPLICATIONS: Stress meter is widely applicable in various meters and indicators. It is used as •

A simple LED meter.

•

Signal level indicator.

•

In Peak detectors.

•

Light, audio, and power meters.

•

Multiple devices can be cascaded for a dot or bar mode display with a range of 60 or 90 dB.

29 •

LM3915s can also be cascaded with LM3914s for a linear/log display or with

LM3916s for an

extended-range VU meter. . .

6.3 BENEFITS:

•

The circuit is absolutely free from ambient light.

•

It is economical and a low budget project.

•

Not a complex circuit.

•

The components are easily available in the market and replaceable.

•

Noise pulse do not have any effect on the circuit.

•

LED’s can withstand the voltage even if no resistors are connected across.

•

Can be used easily to regularly check one’s stress level.

30

APPENDIX PIN DIAGRAM OF LM3915:

31

DEFINITION OF : Absolute Accuracy: The difference between the observed threshold voltage and the ideal threshold voltage for each comparator. Specified and tested with 10V across the internal voltage divider so that resistor ratio matching error predominates over comparator offset voltage. Adjust Pin Current: Current flowing out of the reference adjust pin when the reference amplifier is in the linear region. Comparator Gain: The ratio of the change in output current (ILED) to the change in input voltage (VIN) required to produce it for a comparator in the linear region. http://www.atmel.com/dyn/resources/prod_documents/doc 0368.pdf

32 Dropout Voltage: The voltage measured at the current source outputs required to make the output current fall by 10%. Input Bias Current: Current flowing out of the signal input when the input buffer is in the linear region. LED Current Regulation: The change in output current over the specified range of LED supply voltage (VLED) as measured at the current source outputs. As the forward voltage of an LED does not change significantly with a small change in forward current, this is equivalent to changing the voltage at the LED anodes by the same amount. Line Regulation: The average change in reference output voltage (VREF) over the specified range of supply voltage (V+). Load Regulation: The change in reference output voltage over the specified range of load current (IL (REF)). Offset Voltage: The differential input voltage which must be applied to each comparator to bias the output in the linear region. Most significant error when the voltage across the internal voltage divider is small. Specified and tested with pin 6 voltage (VRHI) equal to pin 4 voltage (VRLO). Relative Accuracy: The difference between any two adjacent threshold points. Specified and tested with 10V across the internal voltage divider so that resistor ratio matching error predominates over comparator offset voltage.

33

LM3915 OUTPUT CHARACTERISTICS:

Output voltage Vs. Output current

34

BIBLIOGRAPHY

Journals: 1. Roberto Bonomi, “Stress and Mind Control”, dated 21/03/2008 Reference Books: 1. Joseph Edminster and Mahmood Nahvi, Electric circuits, Schaum’s Outline, 2003 2. Stanley G Burns and Paul R Bond, Principles of Electronic Circuits, International Thomson publishing, 1997 3. Richard C Jaegar and Travis N Blalock, Micro electronic circuit design, Third Edition Errata, 2008