Classroom seismograph with a scrolling OLED trace (Arduino Uno + MPU6050)

Parts list

Part	Qty	Approx.	Buy
Arduino Uno R3 (CH340 clone)	1	₹450	Buy Arduino Uno R3 (CH340 clone)
MPU6050 module (GY-521)	1	₹150	Buy MPU6050 module (GY-521)
0.96" SSD1306 OLED, I2C, 4-pin	1	₹180	Buy 0.96" SSD1306 OLED, I2C, 4-pin
Active buzzer module	1	₹25	Buy Active buzzer module
Jumper wires + small breadboard	1	₹80	Buy Jumper wires + small breadboard
Heavy base (tile or wooden block) and double-sided tape	1	₹50	Buy Heavy base (tile or wooden block) and double-sided tape
Total		₹935

Affiliate disclosure: “Buy” links may earn FlashReady a small commission at no extra cost to you. Prices are indicative.

Wiring

Every connection
Arduino Uno R3	Part · pin	Wire	Notes
A4	MPU6050 (GY-521) · SDA	blue
A5	MPU6050 (GY-521) · SCL	yellow
5V	MPU6050 (GY-521) · VCC	red	The GY-521 has its own 3.3 V regulator and 3.3 V pull-ups
GND	MPU6050 (GY-521) · GND	black	AD0 left open = address 0x68
SDA	SSD1306 OLED 0.96″ (128×64, I2C) · SDA	blue	The SDA header pin is the same signal as A4
SCL	SSD1306 OLED 0.96″ (128×64, I2C) · SCL	yellow	The SCL header pin is the same signal as A5
5V	SSD1306 OLED 0.96″ (128×64, I2C) · VCC	red
GND	SSD1306 OLED 0.96″ (128×64, I2C) · GND	black
D8	Active buzzer module (high-level trigger) · I/O	orange
5V	Active buzzer module (high-level trigger) · VCC	red
GND	Active buzzer module (high-level trigger) · GND	black

Board quirks: This is a teaching model. A real seismometer measures ground motion thousands of times smaller than a table thump, and India’s official earthquake information comes from the National Center for Seismology. Never present it as a warning system. Tape the MPU6050 flat and firmly to a heavy base. A sensor hanging on its wires records the wires swinging, not the table. Keep it still for the first half second after power-up: the sketch learns the resting 1 g of gravity then and subtracts it from every reading. MPU6050 modules are cheap clones; the noise floor is around 5–10 mg. Footsteps on a wooden stage show up; a person walking past a concrete floor usually doesn’t.

Code

mpu6050-seismograph.inoArduino C++Open in Playground Flash

// Classroom seismograph — Arduino Uno + MPU6050 (GY-521) + 0.96" SSD1306 OLED + active buzzer module.
// Samples the accelerometer 100 times a second, removes the steady 1 g of gravity, and draws the
// shaking as a scrolling trace (one column every 50 ms, newest on the right). Above 0.15 g the
// buzzer sounds. A teaching model of a seismometer — NOT an earthquake warning system.
// MPU6050 and OLED share I2C: SDA → A4, SCL → A5 (MPU6050 0x68, OLED 0x3C). Buzzer I/O → D8.
// Serial (115200): one "time_ms,shake_mg" line per column — open the Serial Plotter.
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

constexpr uint8_t MPU_ADDR = 0x68;
constexpr uint8_t BUZZER_PIN = 8;
constexpr int ALARM_MG = 150;         // shaking (above gravity) that sounds the buzzer
constexpr int FULL_SCALE_MG = 200;    // trace height = this many mg (bigger shakes are clipped)
constexpr uint8_t TRACE_TOP = 16, TRACE_H = 48;

Adafruit_SSD1306 oled(128, 64, &Wire, -1);
int8_t trace[128];                    // one column per 50 ms, in pixels above/below the centre
uint8_t head = 0;
bool mpuOk = false;
long baseline = 1000;                 // |a| at rest in mg, learned while still
int peakMg = 0, windowPeak = 0;
unsigned long lastSample = 0, lastColumn = 0, lastRetry = 0, buzzOff = 0;

bool mpuWrite(uint8_t reg, uint8_t val) {
  Wire.beginTransmission(MPU_ADDR);
  Wire.write(reg);
  Wire.write(val);
  return Wire.endTransmission() == 0;
}

// Magnitude of acceleration in mg (±2 g range: 16384 counts per g), or -1 if the read fails.
long readMagnitudeMg() {
  Wire.beginTransmission(MPU_ADDR);
  Wire.write(0x3B);  // ACCEL_XOUT_H
  if (Wire.endTransmission(false) != 0) return -1;
  if (Wire.requestFrom(MPU_ADDR, (uint8_t)6) != 6) return -1;
  float sum = 0;
  for (uint8_t i = 0; i < 3; i++) {
    uint8_t hi = Wire.read();  // separate statement: read order inside one expression isn't defined
    int16_t raw = (hi << 8) | Wire.read();
    float g = raw / 16384.0;
    sum += g * g;
  }
  return lround(sqrt(sum) * 1000);
}

bool mpuBegin() {
  if (!mpuWrite(0x6B, 0x00)) return false;  // PWR_MGMT_1: wake up, internal clock
  mpuWrite(0x1C, 0x00);                     // ACCEL_CONFIG: ±2 g, the most sensitive range
  mpuWrite(0x1A, 0x03);                     // CONFIG: 44 Hz low-pass filter
  delay(50);
  // Learn the resting value of |a| (≈1000 mg) over half a second. Keep the sensor still.
  long sum = 0;
  uint8_t n = 0;
  for (uint8_t i = 0; i < 50; i++) {
    long m = readMagnitudeMg();
    if (m > 0) sum += m, n++;
    delay(10);
  }
  if (!n) return false;
  baseline = sum / n;
  return true;
}

void drawScreen(int nowMg) {
  oled.clearDisplay();
  oled.setTextSize(1);
  oled.setTextColor(SSD1306_WHITE);
  oled.setCursor(0, 0);
  if (!mpuOk) {
    oled.println(F("Seismograph"));
    oled.println(F("MPU6050 missing!"));
    oled.println(F("Check SDA A4, SCL A5"));
    oled.println(F("and VCC/GND."));
    oled.display();
    return;
  }
  oled.print(F("Now "));
  oled.print(nowMg);
  oled.print(F("mg  Peak "));
  oled.print(peakMg);
  oled.setCursor(0, 8);
  oled.print(peakMg >= ALARM_MG ? F("STRONG SHAKING") : peakMg >= 30 ? F("Felt") : F("Quiet"));
  int mid = TRACE_TOP + TRACE_H / 2;
  for (uint8_t x = 0; x < 128; x += 8) oled.drawPixel(x, mid, SSD1306_WHITE);  // dotted zero line
  for (uint8_t x = 0; x < 128; x++) {
    int8_t v = trace[(head + x) % 128];  // oldest on the left
    oled.drawFastVLine(x, v >= 0 ? mid - v : mid, abs(v) + 1, SSD1306_WHITE);
  }
  oled.display();
}

void setup() {
  Serial.begin(115200);
  pinMode(BUZZER_PIN, OUTPUT);
  Wire.begin();
  if (!oled.begin(SSD1306_SWITCHCAPVCC, 0x3C)) Serial.println(F("OLED not found at 0x3C"));
  oled.clearDisplay();
  oled.setTextColor(SSD1306_WHITE);
  oled.setCursor(0, 0);
  oled.println(F("Seismograph"));
  oled.println(F("Keep still..."));
  oled.display();
  mpuOk = mpuBegin();
  Serial.println(mpuOk ? F("MPU6050 ready. Baseline (mg):") : F("MPU6050 not found - check SDA A4, SCL A5, VCC, GND"));
  if (mpuOk) Serial.println(baseline);
  Serial.println(F("time_ms,shake_mg"));
  drawScreen(0);
}

void loop() {
  unsigned long now = millis();
  if (buzzOff && now > buzzOff) {
    digitalWrite(BUZZER_PIN, LOW);
    buzzOff = 0;
  }
  if (!mpuOk) {
    if (now - lastRetry > 2000) {  // keep trying, so a loose wire can be fixed live
      lastRetry = now;
      mpuOk = mpuBegin();
      if (mpuOk) Serial.println(F("MPU6050 found"));
      drawScreen(0);
    }
    return;
  }

  if (now - lastSample >= 10) {  // 100 samples per second
    lastSample = now;
    long m = readMagnitudeMg();
    if (m < 0) {
      mpuOk = false;
      Serial.println(F("MPU6050 stopped answering"));
      return;
    }
    int dev = m - baseline;
    // Let the baseline follow very slow drift (temperature), not the shaking itself.
    baseline += (m - baseline) / 256;
    if (abs(dev) > abs(windowPeak)) windowPeak = dev;
  }

  if (now - lastColumn >= 50) {  // one trace column per 50 ms → 6.4 s across the screen
    lastColumn = now;
    int mg = windowPeak;
    windowPeak = 0;
    int px = constrain((long)mg * (TRACE_H / 2) / FULL_SCALE_MG, -(TRACE_H / 2 - 1), TRACE_H / 2 - 1);
    trace[head] = px;
    head = (head + 1) % 128;
    // Peak of what is on screen now.
    peakMg = 0;
    for (uint8_t i = 0; i < 128; i++) peakMg = max(peakMg, abs(trace[i]) * FULL_SCALE_MG / (TRACE_H / 2));
    peakMg = max(peakMg, abs(mg));
    if (abs(mg) >= ALARM_MG) {
      digitalWrite(BUZZER_PIN, HIGH);
      buzzOff = now + 1000;
    }
    Serial.print(now);
    Serial.print(',');
    Serial.println(mg);
    drawScreen(abs(mg));
  }
}

// Classroom seismograph — Arduino Uno + MPU6050 (GY-521) + 0.96" SSD1306 OLED + active buzzer module.
// Samples the accelerometer 100 times a second, removes the steady 1 g of gravity, and draws the
// shaking as a scrolling trace (one column every 50 ms, newest on the right). Above 0.15 g the
// buzzer sounds. A teaching model of a seismometer — NOT an earthquake warning system.
// MPU6050 and OLED share I2C: SDA → A4, SCL → A5 (MPU6050 0x68, OLED 0x3C). Buzzer I/O → D8.
// Serial (115200): one "time_ms,shake_mg" line per column — open the Serial Plotter.
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

constexpr uint8_t MPU_ADDR = 0x68;
constexpr uint8_t BUZZER_PIN = 8;
constexpr int ALARM_MG = 150;         // shaking (above gravity) that sounds the buzzer
constexpr int FULL_SCALE_MG = 200;    // trace height = this many mg (bigger shakes are clipped)
constexpr uint8_t TRACE_TOP = 16, TRACE_H = 48;

Adafruit_SSD1306 oled(128, 64, &Wire, -1);
int8_t trace[128];                    // one column per 50 ms, in pixels above/below the centre
uint8_t head = 0;
bool mpuOk = false;
long baseline = 1000;                 // |a| at rest in mg, learned while still
int peakMg = 0, windowPeak = 0;
unsigned long lastSample = 0, lastColumn = 0, lastRetry = 0, buzzOff = 0;

bool mpuWrite(uint8_t reg, uint8_t val) {
  Wire.beginTransmission(MPU_ADDR);
  Wire.write(reg);
  Wire.write(val);
  return Wire.endTransmission() == 0;
}

// Magnitude of acceleration in mg (±2 g range: 16384 counts per g), or -1 if the read fails.
long readMagnitudeMg() {
  Wire.beginTransmission(MPU_ADDR);
  Wire.write(0x3B);  // ACCEL_XOUT_H
  if (Wire.endTransmission(false) != 0) return -1;
  if (Wire.requestFrom(MPU_ADDR, (uint8_t)6) != 6) return -1;
  float sum = 0;
  for (uint8_t i = 0; i < 3; i++) {
    uint8_t hi = Wire.read();  // separate statement: read order inside one expression isn't defined
    int16_t raw = (hi << 8) | Wire.read();
    float g = raw / 16384.0;
    sum += g * g;
  }
  return lround(sqrt(sum) * 1000);
}

bool mpuBegin() {
  if (!mpuWrite(0x6B, 0x00)) return false;  // PWR_MGMT_1: wake up, internal clock
  mpuWrite(0x1C, 0x00);                     // ACCEL_CONFIG: ±2 g, the most sensitive range
  mpuWrite(0x1A, 0x03);                     // CONFIG: 44 Hz low-pass filter
  delay(50);
  // Learn the resting value of |a| (≈1000 mg) over half a second. Keep the sensor still.
  long sum = 0;
  uint8_t n = 0;
  for (uint8_t i = 0; i < 50; i++) {
    long m = readMagnitudeMg();
    if (m > 0) sum += m, n++;
    delay(10);
  }
  if (!n) return false;
  baseline = sum / n;
  return true;
}

void drawScreen(int nowMg) {
  oled.clearDisplay();
  oled.setTextSize(1);
  oled.setTextColor(SSD1306_WHITE);
  oled.setCursor(0, 0);
  if (!mpuOk) {
    oled.println(F("Seismograph"));
    oled.println(F("MPU6050 missing!"));
    oled.println(F("Check SDA A4, SCL A5"));
    oled.println(F("and VCC/GND."));
    oled.display();
    return;
  }
  oled.print(F("Now "));
  oled.print(nowMg);
  oled.print(F("mg  Peak "));
  oled.print(peakMg);
  oled.setCursor(0, 8);
  oled.print(peakMg >= ALARM_MG ? F("STRONG SHAKING") : peakMg >= 30 ? F("Felt") : F("Quiet"));
  int mid = TRACE_TOP + TRACE_H / 2;
  for (uint8_t x = 0; x < 128; x += 8) oled.drawPixel(x, mid, SSD1306_WHITE);  // dotted zero line
  for (uint8_t x = 0; x < 128; x++) {
    int8_t v = trace[(head + x) % 128];  // oldest on the left
    oled.drawFastVLine(x, v >= 0 ? mid - v : mid, abs(v) + 1, SSD1306_WHITE);
  }
  oled.display();
}

void setup() {
  Serial.begin(115200);
  pinMode(BUZZER_PIN, OUTPUT);
  Wire.begin();
  if (!oled.begin(SSD1306_SWITCHCAPVCC, 0x3C)) Serial.println(F("OLED not found at 0x3C"));
  oled.clearDisplay();
  oled.setTextColor(SSD1306_WHITE);
  oled.setCursor(0, 0);
  oled.println(F("Seismograph"));
  oled.println(F("Keep still..."));
  oled.display();
  mpuOk = mpuBegin();
  Serial.println(mpuOk ? F("MPU6050 ready. Baseline (mg):") : F("MPU6050 not found - check SDA A4, SCL A5, VCC, GND"));
  if (mpuOk) Serial.println(baseline);
  Serial.println(F("time_ms,shake_mg"));
  drawScreen(0);
}

void loop() {
  unsigned long now = millis();
  if (buzzOff && now > buzzOff) {
    digitalWrite(BUZZER_PIN, LOW);
    buzzOff = 0;
  }
  if (!mpuOk) {
    if (now - lastRetry > 2000) {  // keep trying, so a loose wire can be fixed live
      lastRetry = now;
      mpuOk = mpuBegin();
      if (mpuOk) Serial.println(F("MPU6050 found"));
      drawScreen(0);
    }
    return;
  }

  if (now - lastSample >= 10) {  // 100 samples per second
    lastSample = now;
    long m = readMagnitudeMg();
    if (m < 0) {
      mpuOk = false;
      Serial.println(F("MPU6050 stopped answering"));
      return;
    }
    int dev = m - baseline;
    // Let the baseline follow very slow drift (temperature), not the shaking itself.
    baseline += (m - baseline) / 256;
    if (abs(dev) > abs(windowPeak)) windowPeak = dev;
  }

  if (now - lastColumn >= 50) {  // one trace column per 50 ms → 6.4 s across the screen
    lastColumn = now;
    int mg = windowPeak;
    windowPeak = 0;
    int px = constrain((long)mg * (TRACE_H / 2) / FULL_SCALE_MG, -(TRACE_H / 2 - 1), TRACE_H / 2 - 1);
    trace[head] = px;
    head = (head + 1) % 128;
    // Peak of what is on screen now.
    peakMg = 0;
    for (uint8_t i = 0; i < 128; i++) peakMg = max(peakMg, abs(trace[i]) * FULL_SCALE_MG / (TRACE_H / 2));
    peakMg = max(peakMg, abs(mg));
    if (abs(mg) >= ALARM_MG) {
      digitalWrite(BUZZER_PIN, HIGH);
      buzzOff = now + 1000;
    }
    Serial.print(now);
    Serial.print(',');
    Serial.println(mg);
    drawScreen(abs(mg));
  }
}

Compiled for uno on avr 1.8.8 with Adafruit SSD1306 2.5.17 · 3 Nov 2026

How it works

A seismograph turns invisible shaking into a picture. This one uses the accelerometer inside an MPU6050 — the same kind of sensor that rotates your phone screen — and draws a scrolling trace on a small OLED, just like the paper drum in a textbook diagram.

How it works

The MPU6050 measures acceleration on three axes. At rest it still reads about 1 g (1000 mg), because gravity pulls on its tiny test mass. The sketch combines the three axes into one magnitude, √(x² + y² + z²), so it doesn’t matter which way the module is mounted, then subtracts the resting value it learned at power-up. What’s left is the shaking.

The Uno reads the sensor over I2C 100 times a second with plain Wire calls (no library — it saves memory for the OLED’s 1 KB screen buffer). Every 50 ms the biggest reading of that window becomes one column of the trace, so the 128-pixel screen shows the last 6.4 seconds. The top line shows the current shaking and the peak on screen in mg; the second line says Quiet, Felt or STRONG SHAKING. Above 150 mg the buzzer sounds for a second.

The Serial Monitor prints time_ms,shake_mg for every column — open Tools → Serial Plotter and the laptop draws a big version of the same seismogram.

What to show at the exhibition

Tap the table softly, then harder: the spikes grow. Ask visitors to guess which tap will set off the buzzer.
Drop a coin from 10 cm and from 30 cm at the same distance: a harder impact gives a bigger spike.
Tap close to the sensor and at the far end of the table: the shaking dies away with distance, which is why earthquakes are felt most near the epicentre.
Put a chart beside it explaining P-waves (arrive first, push–pull) and S-waves (arrive later, side to side) and the Richter/moment-magnitude idea.

Questions the examiner may ask

Why does a still sensor read 1 g? An accelerometer measures the force on its test mass; gravity pulls on it all the time, so at rest it reads 1 g upwards.
What is mg? One-thousandth of g (9.81 m/s²), so 150 mg ≈ 1.5 m/s².
How is this different from a real seismometer? Real ones detect ground movement of nanometres, are buried on bedrock away from traffic, and record at precise times from GPS so several stations can locate the epicentre.
Why 100 samples per second? Shaking of a table or a building is mostly below 20 Hz; sampling well above twice that frequency (the Nyquist rule) captures it.
What does the low-pass filter do? The MPU6050’s built-in 44 Hz filter removes fast electrical noise before the Uno reads the value.

Cost in India

About ₹950: the GY-521 module is ₹120–180 and the OLED ₹150–220 at local shops or online. No extra resistors are needed — the GY-521 has its own regulator and pull-ups.

Troubleshooting

The OLED says “MPU6050 missing!”

No reply at 0x68. Check SDA on A4 and SCL on A5 (not swapped), VCC and GND. If AD0 is tied to 3.3 V the address is 0x69 — leave AD0 open. The sketch retries every 2 s, so it recovers as soon as the wire is fixed.

The trace is never flat

Something is vibrating — a fan on the same table, or the board was moved after power-up. Press the Uno’s reset with everything still to learn a new baseline.

The buzzer goes off at every small tap

Raise ALARM_MG from 150 to 300 for a demo on a light table.

Blank OLED

Some 0.96" OLEDs are at 0x3D. Change 0x3C in oled.begin(), or run an I2C scanner to see both addresses.

Upgrades

Log the trace to a microSD card with a timestamp from a DS3231 RTC.
Build a “shake table” from a cardboard box on pencils and compare model buildings with and without cross-bracing.
Send the Serial CSV to a laptop and compute the dominant frequency with a spreadsheet FFT.
Use three axes separately to tell side-to-side (S-wave-like) from up-down (P-wave-like) motion.

Parts list

Wiring

Code

How it works

How it works

What to show at the exhibition

Questions the examiner may ask

Cost in India

Troubleshooting

Upgrades

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