ECG Project using Arduino with AD8232 Heart Sensor

This project builds a working single-lead electrocardiograph: an Arduino Uno reads the heart's electrical signal through an AD8232 ECG sensor module and displays the live waveform on a 0.96-inch OLED screen with a heart-rate readout in beats per minute. The real engineering challenge is scale — the signal at the skin is roughly 1 mV (design-level figure), while the body also picks up mains interference many times larger, and the DC offset from electrode gel can reach ±300 mV (datasheet value). The AD8232 solves this with a classic analog chain: an instrumentation amplifier with a gain of 100 (datasheet value) rejects what both electrodes see in common, and a right-leg-drive amplifier actively cancels the 50 Hz mains hum before it swamps the trace. Three adhesive gel electrodes, a small breadboard circuit and firmware that samples, peak-detects and plots the waveform complete the build. It is designed strictly as an academic prototype for learning biopotential signal conditioning — not as certified medical equipment.

1. Three adhesive gel electrodes are placed on the chest or forearms with the 3-wire lead snapped on — electrode placement and fresh gel contact is the single biggest factor in trace quality, and beats any firmware tweak.
2. The AD8232's instrumentation amplifier reads the differential signal between two electrodes at a gain of 100 (datasheet value), tolerating up to ±300 mV of skin-electrode DC offset (datasheet value).
3. The right-leg-drive circuit senses common-mode mains interference and drives its inverse into the third electrode, cancelling most 50 Hz hum before amplification.
4. Two-pole high-pass and three-pole low-pass filter stages inside the AD8232 shape the signal band; the rail-to-rail output feeds Arduino analog pin A0.
5. The Arduino samples the output at approximately 100 samples per second (design target) and pushes the points to the OLED as a scrolling trace over I2C.
6. An R-peak detector (threshold crossing with refractory lockout) measures beat-to-beat intervals and converts the rolling average of the last 8 beats (design target) into beats per minute on the display.
7. The firmware polls the LO+ and LO− leads-off pins continuously; if either flags, the waveform pauses and the display notes the electrode check until contact is restored.

Tech stack:

• Arduino Uno (ATmega328P)
• AD8232 single-lead ECG module
• 0.96-inch OLED · I2C (SSD1306)
• Arduino IDE · C++ firmware
• 3-wire ECG electrode lead + gel electrodes
• USB serial link (debug + plotter)

• [Single-lead ECG acquisition] The AD8232 module picks up surface biopotentials of roughly 1 mV (design-level figure) through three adhesive gel electrodes, with a datasheet instrumentation-amplifier gain of 100 and acceptance of up to ±300 mV of electrode DC offset.
• [Right-leg-drive mains rejection] The AD8232's right-leg-drive amplifier senses the body's common-mode voltage and drives an inverted copy back into the right-leg electrode, actively cancelling 50 Hz mains hum before it swamps the heart signal; the instrumentation amplifier (80 dB CMRR from dc to 60 Hz, datasheet value) then amplifies only the differential — the actual heartbeat.
• [Live OLED waveform] A 0.96-inch 128 × 64 OLED draws a scrolling real-time ECG trace fed by the Arduino sampling the AD8232 output at approximately 100 samples per second (design target), so the P-QRS-T morphology is visible during the demo.
• [R-peak heart-rate readout] Firmware detects R-peaks with a threshold crossing plus a refractory lockout and computes beats per minute over a rolling window of the last 8 beats (design target), shown beside the waveform.
• [Leads-off detection] The AD8232's LO+ and LO− pins flag the moment an electrode peels or loses contact; firmware pauses the trace and notes the electrode check instead of flatlining silently — a strong viva talking point.
• [Fast-restore after motion] When electrode movement saturates the filter stages, the AD8232's fast-restore circuit shortens the settling time so the trace recovers in a fraction of a second instead of drifting (datasheet behavior).
• [Serial plotter debugging] Raw samples stream over USB to the Arduino IDE serial plotter, giving a second large-screen view of the waveform for calibration and viva demonstration.

• Assembled and tested prototype (Arduino Uno, AD8232 module, OLED, 3-wire electrode lead, breadboard wiring)
• Complete firmware source code (Arduino IDE, commented)
• Wiring diagram and component list
• Electrode placement and skin-preparation guide (placement and gel contact quality is the single biggest factor in trace quality)
• Project report PDF (background, AD8232 signal-chain theory, methodology, results)
• PPT presentation for final review
• Viva Q&A preparation document (instrumentation amplifiers, right-leg drive, ECG basics, leads-off detection)