top of page

  Heartbeat Sensor Circuit Project 

PROJECT OVERVIEW:

Technologies: IR LED & Receiver, LM358 Dual Op-Amp, Breadboard, Resistors, Capacitors, 9V DC Supply

​

This project involved designing and implementing an analog heart-rate monitoring circuit capable of detecting human pulse signals in real time. The system utilized an infrared LED and photodiode pair to detect variations in light intensity caused by the changing blood volume in a fingertip. Each heartbeat alters the reflectivity of blood, producing a minute voltage fluctuation which is then amplified and filtered using the LM358 operational amplifier configured in a dual-stage setup.

The first op-amp stage provided signal amplification, converting weak analog pulses into a readable voltage range, while the second stage incorporated low-pass filtering to remove high-frequency noise and produce a stable, smooth waveform. The processed signal was then used to drive an LED indicator, flashing in rhythm with the detected heartbeat, and simultaneously output to an oscilloscope for real-time visualization of the pulse waveform.

By avoiding the use of microcontrollers, the focus was placed entirely on core analog circuit design, signal conditioning, and real-time instrumentation highlighting a practical understanding of both electronic fundamentals and biomedical signal interpretation.

​

​

          KEY TECHNICAL CONTRIBUTION:

  • Analog Signal Acquisition: Designed an infrared reflection-based sensor circuit to detect pulse signals via optical variation.

  • Dual-Stage Amplification: Configured an LM358 op-amp to amplify millivolt-level bio-signals to 0–5 V, enabling LED visualization and oscilloscope analysis.

  • Noise Filtering & Stability: Implemented RC filters and proper grounding to suppress power-line interference and ambient light noise.

  • Waveform Visualization: Interfaced the analog output with an oscilloscope, measuring waveform amplitude, timing, and frequency for accuracy verification.

  • Circuit Optimization: Fine-tuned resistor-capacitor values to balance gain, response time, and signal clarity without distortion or clipping.

  • Hardware Debugging: Conducted iterative breadboard testing, continuity checks, and calibration under variable lighting conditions.

​

LEARNING OUTCOMES:

  • Developed a strong grasp of biomedical instrumentation principles, particularly optical pulse sensing and analog front-end design.

  • Strengthened circuit-level understanding of op-amp configuration, frequency response, impedance matching, and signal stability.

  • Gained hands-on proficiency with oscilloscopes, breadboarding, and component-level troubleshooting.

  • Learned to document hardware performance metrics such as gain, bandwidth, and signal-to-noise ratio for validation.

  • Built a foundation for embedded biomedical systems, bridging electrical engineering with real-world health monitoring applications.

bottom of page