AD8232 ECG Signal Noisy? Fix 50 Hz Hum and Power Noise

Is this your problem?

If two or more of these sound familiar, power and mains coupling are your prime suspects:

• The trace looks thick or fuzzy, even when you sit still
• It gets much cleaner when the laptop charger is unplugged
• The baseline drifts slowly up and down
• Random spikes appear when Wi-Fi or a motor is active
• It’s worse near a fan, tube light or extension board
• The QRS peaks are there, but P and T waves are lost

Why it happens, in one picture

The AD8232 amplifies a 1 mV signal about a thousand times. Anything that sneaks in before or alongside that signal is amplified or added too. Four things usually do it, and the biggest isn’t the board at all.

The 2-minute test: is it power or the electrodes?

The fix in 3 steps

1. Cut the link to mainsRun the laptop on battery while you record, or build the project on batteries (for example 3× AA or a 1-cell Li-ion pack feeding the regulator). Safer, and it removes the biggest noise path.
2. Give the AD8232 its own clean 3.3 VFeed a dedicated low-noise 3.3 V regulator and use it only for the AD8232, and on an Arduino also for AREF. Then call analogReference(EXTERNAL) first in setup(). The ECG output sits around the middle of 0–3.3 V, so a 3.3 V reference also gives you more resolution than 5 V.
3. Fresh electrodes, still body, 50 Hz filterUse new gel pads on clean skin, keep the lead cable still and away from power cords, and remove leftover 50 Hz in code (below).

Remove 50 Hz in code (works on any Arduino)

Sample at exactly 500 times per second and average the last 10 samples. That’s 20 ms, exactly one 50 Hz cycle, so the hum averages to zero (and so does 100 Hz).

const int N = 10;               // 10 samples x 2 ms = 20 ms = one 50 Hz cycle
int buf[N]; int idx = 0; long sum = 0;
unsigned long next = 0;

void setup() {
  analogReference(EXTERNAL);    // clean 3.3 V on AREF: FIRST line
  Serial.begin(115200);
  pinMode(10, INPUT);           // LO+
  pinMode(11, INPUT);           // LO-
}

void loop() {
  if ((long)(micros() - next) < 0) return;
  next += 2000;                 // 500 samples per second
  if (digitalRead(10) || digitalRead(11)) {   // an electrode is off
    Serial.println(0);
    return;
  }
  int v = analogRead(A0);
  sum += v - buf[idx]; buf[idx] = v; idx = (idx + 1) % N;
  Serial.println(sum / N);      // 50 Hz and 100 Hz removed
}

In a 60 Hz country, sample at 600 per second (next += 1667) with the same N = 10. This filter also softens the sharp QRS peak a little: fine for heart rate, not for detailed waveform analysis.

Which setup are you using?

Still noisy? The other common causes

Frequently asked questions

© Ramanu Systems · Precision electronics modules, Made in India · This article is for learning and hobby projects only and is not medical advice. AD8232 figures from Analog Devices. Pin numbers follow the SparkFun AD8232 hookup guide. Regulator figures from the Texas Instruments TPS7A20 datasheet. Found an error? Tell us and we will fix it and credit you.