Protocentral easyECG — Single-Lead ECG Breakout, Qwiic / STEMMA QT

Protocentral easyECG is a single-lead ECG breakout that doesn’t hide the interesting part. Most ECG boards put the whole front end inside one chip, so all you ever see is the output. We built easyECG from parts you can point at: a TI INA333 instrumentation amplifier, two OPA2333 op-amps and a TLA2024 12-bit ADC. Plug it into any Qwiic / STEMMA QT host, stick on three electrodes, and you’ll see your heartbeat in the free OpenView desktop app in minutes.

The board explains itself. Flip it over and the whole signal chain is printed on the back: input protection, in-amp ×11, 0.5 Hz high-pass, gain ×49, 31 Hz low-pass, 12-bit ADC. Turn it back and the key nodes have labelled test points: INA OUT, OUT, DRL and VMID, plus a GND point for your probe clip. Put a scope on them and you can watch each stage do its job. You’ll see the electrode offset that the high-pass removes, a 1 mV R-wave becoming half a volt, and the right-leg drive holding the common mode where it belongs.

Built for the lab bench. Every stage is a circuit from an analog-electronics textbook, so easyECG works as a biomedical-instrumentation or filter-design lab as well as a heart-rate sensor. Boards ship at I²C address 0x49, so an easyECG and an easyEMG share one Qwiic bus without touching a jumper. Full schematics and layout are open (CERN-OHL-P v2), and the library is MIT-licensed.

See it in OpenView

The library’s 04.OpenView example streams the ECG, the heart rate and a signal check to OpenView, the free desktop app for live plotting and recording. It needs OpenView 3.4 or later, which adds the easyECG profile. If an electrode comes off, the Signal tile says so.

Features

• Discrete, probeable ECG front end: INA333 in-amp (×11) → RC high-pass (0.5 Hz) → OPA2333 gain stage (×48.6) → Sallen-Key low-pass (31 Hz) → TLA2024 12-bit ADC
• Signal-chain block diagram printed on the back; labelled test points on the front, plus a GND point for your probe clip
• Driven-right-leg circuit with 10 MΩ input bias and a 390 kΩ current limit (≤ 4.2 µA into the body)
• ESD array and RF filtering on the electrode inputs
• Qwiic / STEMMA QT ×2 for daisy-chaining, plus a 0.1″ header that takes 3.3 V or 5 V hosts
• Arduino library with a 50/60 Hz notch, a 40 Hz low-pass and Pan-Tompkins heart-rate detection
• Open-source hardware (CERN-OHL-P v2) and software (MIT)

Use it for

• Biomedical instrumentation and analog-filter labs: measure the gain of each stage, plot the frequency response, see why the right-leg drive matters
• Embedded and DSP courses: I²C, sampling, digital notch filters, R-peak detection
• Physiology practicals: Lead I placement, heart rate at rest and after exercise
• Your first heart-rate project on an Arduino, ESP32, RP2040 or Raspberry Pi

Specifications

• Lead: single lead (Lead I), 3 electrodes (LA, RA, RL) on a 3.5 mm TRS jack
• Gain: ×535 total (×11 in-amp, ×48.6 second stage)
• Bandwidth: 0.5 – 31 Hz (analog, −3 dB)
• Input range: ±3.1 mV; electrode offset tolerance ±145 mV
• Resolution: 12-bit, 1.87 µV per count referred to the electrodes
• Sample rate: up to 1 kSPS host-paced (500 SPS on AVR Arduinos)
• Interface: I²C / Qwiic, address 0x49 (0x48 via the ADDR jumper)
• Supply: 3.3 – 5 V on the header; 3.3 V on Qwiic
• Board: 40.0 × 28.8 mm, 4 × M2 mounting holes

Qwiic cable not included. Use any Qwiic / STEMMA QT cable, or wire the 0.1″ header instead. Qwiic runs at 3.3 V; on a 5 V host, use the header.

Use a battery-powered host, or easyISO

Here’s the honest limitation: on a mains-powered computer, leakage current through the USB ground drives the right-leg circuit to its rail, and you get a flat line, not a noisy trace. Run your laptop on battery, use a battery-powered microcontroller, or put an easyISO isolated Qwiic adapter between the host and easyECG. The same applies to test equipment: probe the test points with a battery-powered scope or use an ECG simulator. A mains-earthed bench scope connects the person wearing the electrodes to earth.

Important notice

easyECG is for education, research and experimentation. It is not a medical device and must not be used for diagnosis or monitoring of any medical condition.

Browse the source on GitHub