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ElectronicsSchool ProjectsMarch 2025

ECG HMI

Integrated portable ECG device: flexible cleanroom-fabricated electrodes, STM32 acquisition card and LED display. Complete multidisciplinary biomedical project.

ECG HMI

ECG HMI - Complete Electrocardiographic Device

Overview

Design and realization of an integrated portable ECG device, combining cleanroom microfabrication, embedded electronics, and display interface. Multidisciplinary project covering the entire biomedical measurement chain: from sensors to real-time visualization.

Objectives

Develop a functional electrocardiogram prototype integrating:

  • Custom-fabricated ECG electrodes in cleanroom
  • Acquisition card for signal processing
  • Display interface (OLED/LED matrix)

Technologies Used

Microfabrication

  • Photolithography: Electrode structuring
  • Vacuum evaporation: Ti/Au and organic layer deposition
  • PEDOT:PSS: Conductive polymer for impedance improvement
  • Kapton (polyimide): Flexible substrate for electrodes

Electronics & Programming

  • STM32: Microcontroller for signal processing
  • CMSIS-DSP: Library for FIR filtering
  • UART: Serial communication for visualization
  • PCB fabrication (SMD components, reflow)

Characterization

  • Impedance spectroscopy: Electrode performance measurement
  • Ellipsometry: Layer thickness control
  • Oscilloscope: ECG signal validation

System Architecture

ECG System Synoptic

1. ECG Electrodes (Cleanroom)

Fabrication process:

  1. Flexible Kapton substrate
  2. O₂ plasma treatment for activation
  3. Photolithography (S1813 photoresist)
  4. Ti/Au evaporation (100nm)
  5. Lift-off and cleaning
  6. PEDOT:PSS coating

Performance:

  • Impedance ~7 Ω (comparable to commercial electrodes)
  • Water-only operation (no conductive gel)
  • Nyquist diagram compliant

2. ECG Acquisition Card

Fabrication:

  • SMD components soldered by reflow (stencil + hot plate)
  • ±15V power supply
  • Test points for validation

Signal processing:

  • ECG signal capture via electrodes
  • FIR filtering (CMSIS-DSP)
  • UART transmission to Serial Plot
  • Real-time visualization

3. Display Matrix

OLED attempt:

  • Multilayer architecture (ITO/HTL/EML/ETL/Al)
  • Thermal and co-evaporation
  • Real-time thickness monitoring (Inficon)
  • Nitrogen encapsulation

Alternative solution - 8×8 LED Matrix:

  • Multiplexing card fabricated
  • Adapted programming (eCampus library)
  • Functional scrolling text display

Technical Challenges

Microfabrication

  • Control of deposition uniformity
  • Environmental management (oxygen, humidity)
  • Lift-off process precision

Electronics

  • SMD component soldering (defective vias)
  • Methodical debugging of multiplexing card
  • Multi-filter processing stability

OLED

  • Oxygen spike during chamber opening (machine fault)
  • Missing HBL layer → excessive voltages (13-20V)
  • Matrix non-functional outside neutral environment

Learnings

Technical Skills

  • Mastery of cleanroom techniques (photolithography, evaporation)
  • Optical and electrical component characterization
  • Real-time biomedical signal processing
  • Electronic circuit fabrication and debugging

Methodology

  • Importance of scientific rigor (impact of attention errors)
  • Systematic and methodical debugging
  • Adaptation to hardware constraints
  • Multidisciplinary integration (chemistry, physics, electronics, computer science)

Innovation

  • Development of gel-free biomedical electrodes
  • Complete portable medical device architecture
  • Mastery of complete chain: sensor → processing → display