Stress‑Meter: Standalone Thumb‑Press Stress Detection Device

First‑year BTech Electrical Engineering project (2020–21): NI Multisim simulation of a standalone stress‑meter activated by thumb‑press sensor

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Table of Contents

• Project Overview
• Circuit Design & Operation
• Technical Specifications
• Folder Structure
• Installation & Simulation
• Data & Results
• Contributors
• Contact

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Project Overview

This project simulates a standalone stress‑meter that activates when the user presses their thumb on a sensor pad. The device amplifies skin‑conductance variations and displays stress levels on a logarithmic LED bar, with an audio alert for high stress.

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Circuit Schematic

Signal Amplification

• Transistor Stage: A BC548 (T1) configured as a common‑emitter amplifier boosts voltage changes from the thumb sensor pad. The base is driven through resistor R1 and adjustable via potentiometer VR1 to set sensitivity.
• Biasing & Stabilization: Diode D1 provides stable bias for T1’s base; capacitor C1 decouples the emitter, ensuring steady amplification without oscillations.

Logarithmic LED Display

• Driver IC: Amplified signal feeds LM3915 (IC1), which drives five LEDs (pins 14–18) in logarithmic increments of ~125 mV per step. LED1 lights at 150 mV; LED5 and buzzer activate at ≥650 mV.
• Alarm Mechanism: R4, R5, and C2 form the LED flashing circuit; when stress threshold is exceeded, LED5 flashes and piezo buzzer PZ1 beeps.

Power Regulation

• Supply: Zener diode ZD1 with R6 establishes a 5 V regulated rail.
• Decoupling: Capacitor C3, placed close to IC1’s supply pin, filters noise and prevents false triggering.

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Technical Specifications

| Component | Value / Type | Purpose | | BC548 (T1) | NPN transistor, common‑emitter | Signal amplification | | LM3915 (IC1) | Logarithmic LED driver | Stress‑level display | | R1, VR1 | 10 kΩ + 10 kΩ potentiometer | Input bias & sensitivity adjustment | | R3 | 220 Ω | LED current limiting (~20 mA) | | R4, R5, C2 | 1 kΩ, 10 µF | LED flash oscillator | | ZD1, R6 | 5 V Zener + 1 kΩ | Voltage regulation | | C1, C3 | 100 nF each | Decoupling | | PZ1 | Piezo buzzer | Audio alert |

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Folder Structure

stress‑meter/
├── README.md                     # Project overview and instructions  
├── docs/
│   ├── slides.pdf                # Presentation PDF  
│   └── slides.pptx               # Original PPTX  
├── simulation/
│   ├── multisim/                 # NI Multisim files  
│   └── results.csv               # Voltage vs. LED state data  
├── src/                          # Placeholder for future code  
└── assets/
    ├── schematic.png             # Circuit diagram screenshot  
    └── demo.gif                  # Simulation animation  

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Installation & Simulation

1. Clone the repo

   git clone https://github.com/Siddharthsinghkumar/stress-meter.git  
   cd stress-meter  

2. Open in NI Multisim

   • Load simulation/multisim/stress-meter.ms14
   • Run transient analysis to view LED thresholds.

3. View Slides

   • Open docs/slides.pdf for design rationale and test results.

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Data & Results

The results.csv includes time‑stamped voltage readings and illuminated LED count:

• time_ms: Simulation time (ms)
• vin_mV: Input pad voltage (mV)
• led_count: Number of LEDs lit (0–5)
• alarm: 1 when buzzer activates

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Contributors

Siddharth Singh: Circuit analysis and Multisim simulation Friend A: Presentation slides Friend B: Project report

Contact

Siddharth Singh

• GitHub: Siddharthsinghkumar
• LinkedIn: siddharth-singh-735340296
• Email: [email protected]