Your classmates used a stopwatch. You have a data logger.

Imagine this: Chemistry lab. Reaction rate experiment. Everyone drops Alka-Seltzer in water and times how long until bubbling stops with a stopwatch. One data point per trial. Rough.

You drop the tablet and your DS18B20 records temperature every second for 5 minutes. You get 300 data points. You plot the curve: temperature rises 2.3°C in 45 seconds (exothermic), then slowly returns to baseline. You compare cold water vs. hot water vs. salt water. You show the effect of temperature on reaction rate — with actual temperature measurements, not just observation.

That’s what we’re building. For about $22.

What you’ll need

You also need: 4.7kΩ resistor (comes with most breadboard kits), beakers or glasses, Alka-Seltzer tablets, water at different temperatures.

Total: ~$22 | Time: ~1–2 hours | Difficulty: ●●○○○

How it works (60 seconds)

The DS18B20 is a digital thermometer in a waterproof stainless steel probe. It communicates on a 1-Wire bus — one data wire, plus power and ground. The sensor contains a tiny computer that measures temperature and sends it as a precise digital number (±0.5°C accuracy).

When a reaction is exothermic (releases heat), the water temperature rises. The faster the reaction, the faster the temperature rises. By measuring temperature every second, you can calculate the rate (°C per second = proxy for reaction speed).

Step 0: Design your experiment

Hypothesis options (pick one):

• “Higher initial water temperature = faster reaction rate (measured by °C rise per second)”
• “Crushed tablet reacts faster than whole tablet”
• “Salt water changes the reaction rate vs. plain water”

Variables:

Run each trial twice and average the results.

Step 1: Wire it up

Time: ~10 minutes

The DS18B20 has 3 wires in a specific order (check your sensor’s datasheet):

• Red = VCC (3.3V)
• Black = GND
• Yellow/White = Data (one-wire signal)

1. DS18B20 Red → 3.3V
2. DS18B20 Black → GND
3. DS18B20 Yellow → board GPIO 4 (C6: GPIO 0)
4. 4.7kΩ resistor between GPIO 4 (C6: GPIO 0) and 3.3V (pull-up — REQUIRED)

OLED: 5. SDA → board GPIO 8 (C6: GPIO 6) 6. SCL → board GPIO 9 (C6: GPIO 7) 7. VCC → 3.3V 8. GND → GND

Check: The 4.7kΩ pull-up resistor is not optional — without it, the 1-Wire protocol won’t work. Most breadboard component kits include resistors; look for “4.7K” or color code: yellow-violet-red.

Step 2: Flash the code

Time: ~20 minutes

Install libraries: OneWire (by Paul Stoffregen), DallasTemperature, Adafruit SSD1306, Adafruit GFX Library

The big picture first. This program is a web-controlled chemistry data logger:

• The DS18B20 probe sits in the beaker and reports the water temperature once per second.
• The web interface on your phone shows the live temperature and has Start/Stop buttons — so you can control the recording while your hands are busy dropping the tablet.
• After the trial, you download a CSV file with every second of data, including how many degrees the temperature changed from baseline.

A program is like a recipe. The computer reads it top to bottom and does exactly what is written, nothing more. Copy this entire recipe into Arduino IDE and upload it:

// ========== CHOOSE YOUR BOARD ==========
// Uncomment the line for YOUR board:
#define BOARD_S3    // ESP32-S3-DevKitC-1
//#define BOARD_C6  // ESP32-C6-DevKitC-1
// ========================================

#ifdef BOARD_S3
  #define PIN_ONEWIRE          4
  #define PIN_SDA              8
  #define PIN_SCL              9
#endif
#ifdef BOARD_C6
  #define PIN_ONEWIRE          0
  #define PIN_SDA              6
  #define PIN_SCL              7
#endif

#include <OneWire.h>
#include <DallasTemperature.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <WiFi.h>
#include <WebServer.h>

OneWire oneWire(PIN_ONEWIRE);
DallasTemperature sensors(&oneWire);
Adafruit_SSD1306 display(128, 64, &Wire, -1);

const char* ssid = "YOUR_WIFI_NAME";
const char* password = "YOUR_WIFI_PASSWORD";
WebServer server(80);

float tempLog[600];
unsigned long timeLog[600];
int logCount = 0;
bool recording = false;
float baselineTemp = 0;
unsigned long recordStart = 0;

void startRecording() {
  logCount = 0;
  recording = true;
  recordStart = millis();
  sensors.requestTemperatures();
  baselineTemp = sensors.getTempCByIndex(0);
  Serial.println("Recording started. Baseline: " + String(baselineTemp, 2) + "C");
}

void stopRecording() {
  recording = false;
  Serial.println("Recording stopped. " + String(logCount) + " points.");
}

void setup() {
  Serial.begin(115200);
  sensors.begin();
  Wire.begin(PIN_SDA, PIN_SCL);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) delay(500);
  Serial.println("IP: " + WiFi.localIP().toString());
  
  server.on("/", []() {
    String html = "<!DOCTYPE html><html><head><meta name='viewport' content='width=device-width,initial-scale=1'>";
    html += "<title>Reaction Logger</title>";
    html += "<style>body{font-family:sans-serif;padding:20px}button{padding:12px 20px;margin:5px;font-size:16px;border-radius:6px;border:none;cursor:pointer}";
    html += ".start{background:#4CAF50;color:white}.stop{background:#f44336;color:white}.dl{background:#2196F3;color:white}</style></head><body>";
    html += "<h2>Reaction Rate Logger</h2>";
    
    sensors.requestTemperatures();
    float t = sensors.getTempCByIndex(0);
    html += "<p>Current temp: <b>" + String(t, 2) + " C</b></p>";
    html += "<p>Status: <b>" + String(recording ? "RECORDING" : "IDLE") + "</b> | Points: " + String(logCount) + "</p>";
    html += "<button class='start' onclick=\"fetch('/start')\">Start Recording</button>";
    html += "<button class='stop' onclick=\"fetch('/stop')\">Stop Recording</button>";
    html += "<button class='dl' onclick='window.location=\"/csv\"'>Download CSV</button>";
    html += "</body></html>";
    server.send(200, "text/html", html);
  });
  
  server.on("/start", []() {
    startRecording();
    server.send(200, "text/plain", "started");
  });
  
  server.on("/stop", []() {
    stopRecording();
    server.send(200, "text/plain", "stopped");
  });
  
  server.on("/csv", []() {
    String csv = "time_s,temp_C,delta_C\n";
    for (int i = 0; i < logCount; i++) {
      csv += String(timeLog[i]/1000.0, 1) + "," + String(tempLog[i], 2) + "," + String(tempLog[i] - baselineTemp, 2) + "\n";
    }
    server.send(200, "text/csv", csv);
  });
  
  server.begin();
  display.clearDisplay();
  display.display();
}

unsigned long lastSample = 0;

void loop() {
  server.handleClient();
  
  if (millis() - lastSample > 1000) {
    lastSample = millis();
    sensors.requestTemperatures();
    float temp = sensors.getTempCByIndex(0);
    
    if (recording && logCount < 600) {
      tempLog[logCount] = temp;
      timeLog[logCount] = millis() - recordStart;
      logCount++;
      Serial.println(String(timeLog[logCount-1]/1000.0, 1) + "," + String(temp, 2));
    }
    
    display.clearDisplay();
    display.setTextSize(1);
    display.setCursor(0, 0);
    display.println(recording ? "RECORDING" : "READY");
    
    display.setTextSize(2);
    display.setCursor(0, 16);
    display.println(String(temp, 1) + " C");
    
    if (recording && logCount > 0) {
      float delta = temp - baselineTemp;
      display.setTextSize(1);
      display.setCursor(0, 40);
      display.println("Change: +" + String(delta, 2) + " C");
      display.setCursor(0, 52);
      display.println("t=" + String((millis()-recordStart)/1000) + "s n=" + String(logCount));
    }
    
    display.display();
  }
}

Line-by-line: what every line does and why

Lines 1–7: Borrowing ready-made instruction books

#include <OneWire.h>
#include <DallasTemperature.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <WiFi.h>
#include <WebServer.h>

#include means “grab this instruction book.” OneWire handles the 1-Wire communication protocol — a clever way to send digital data over a single wire. DallasTemperature knows how to talk to DS18B20 sensors specifically (Dallas was the company that invented them). The rest handle the display, WiFi, and web server.

Lines 9–12: Sensor and display setup

#define PIN_ONEWIRE          4
OneWire oneWire(PIN_ONEWIRE);
DallasTemperature sensors(&oneWire);
Adafruit_SSD1306 display(128, 64, &Wire, -1);

PIN_ONEWIRE 4 means the sensor data wire plugs into leg 4 (C6: leg 0). OneWire oneWire(PIN_ONEWIRE) creates the 1-Wire bus on that leg. DallasTemperature sensors(&oneWire) creates the temperature sensor system using that bus — the & means “use the address of oneWire, do not copy it.” Think of it like giving someone directions to a location rather than moving the location.

Lines 17–23: Data storage

float tempLog[600];
unsigned long timeLog[600];
int logCount = 0;
bool recording = false;
float baselineTemp = 0;
unsigned long recordStart = 0;

Two shelves of 600 compartments: one for temperatures, one for timestamps. 600 entries at 1 per second = 10 minutes of data. recording is a true/false flag. baselineTemp is the water temperature at the moment you tap “Start” — all delta calculations compare against this. recordStart is the clock time when recording began — so timestamps in the CSV are “seconds since start,” not “milliseconds since power-on.”

Lines 25–31: startRecording() and stopRecording()

void startRecording() {
  logCount = 0;
  recording = true;
  recordStart = millis();
  sensors.requestTemperatures();
  baselineTemp = sensors.getTempCByIndex(0);
}

Reset the log count to 0 (start fresh). Set the recording flag. Save the current time as the start reference. sensors.requestTemperatures() tells the DS18B20 to start measuring — it takes about 750ms to complete a 12-bit temperature conversion. getTempCByIndex(0) retrieves the result from the first (index 0) sensor on the bus.

void stopRecording() {
  recording = false;
}

Just flip the flag. The data stays in the arrays until the next Start.

Lines 33–90: setup() — morning routine

sensors.begin();
Wire.begin(PIN_SDA, PIN_SCL);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);

Start the temperature sensor library. Start the I2C bus on legs 8 and 9 (C6: legs 6 and 7). Start the display at address 0x3C.

WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) delay(500);
Serial.println("IP: " + WiFi.localIP().toString());

Connect to WiFi. Keep waiting, checking every 500 ms, until connected. Print the IP address — you need this to open the control panel on your phone.

server.on("/", []() { ... server.send(200, "text/html", html); });

Register the main page handler using a lambda — a mini function with no name, written right inside the parentheses. Every time a phone visits the main page, it reads the live temperature and shows Start/Stop/Download buttons.

server.on("/start", []() {
  startRecording();
  server.send(200, "text/plain", "started");
});

When the phone taps “Start Recording,” it sends a request to /start. This handler calls startRecording() and sends back “started” as confirmation.

server.on("/csv", []() {
  String csv = "time_s,temp_C,delta_C\n";
  for (int i = 0; i < logCount; i++) {
    csv += String(timeLog[i]/1000.0, 1) + "," + String(tempLog[i], 2) + "," + String(tempLog[i] - baselineTemp, 2) + "\n";
  }
  server.send(200, "text/csv", csv);
});

Build the download file. timeLog[i]/1000.0 converts milliseconds to seconds. tempLog[i] - baselineTemp is the temperature change from the start — your ΔT column. \n ends each row. The three columns become your X, Y1, Y2 in Google Sheets.

Lines 92–127: loop() — runs forever

server.handleClient();

Must be in every loop() iteration — this is what makes the web server respond to phone taps.

if (millis() - lastSample > 1000) {
  lastSample = millis();
  sensors.requestTemperatures();
  float temp = sensors.getTempCByIndex(0);

Every second, ask the sensor for a new reading. requestTemperatures() triggers the measurement. getTempCByIndex(0) retrieves the result in Celsius.

  if (recording && logCount < 600) {
    tempLog[logCount] = temp;
    timeLog[logCount] = millis() - recordStart;
    logCount++;
    Serial.println(String(timeLog[logCount-1]/1000.0, 1) + "," + String(temp, 2));
  }

Only save if recording is active AND there is still space in the array. Store the temperature and elapsed time. logCount++ advances the pointer after storing (so it writes to the current slot, then moves forward). Print to Serial for backup.

  display.println(recording ? "RECORDING" : "READY");
  display.setTextSize(2);
  display.println(String(temp, 1) + " C");
  if (recording && logCount > 0) {
    float delta = temp - baselineTemp;
    display.println("Change: +" + String(delta, 2) + " C");
    display.println("t=" + String((millis()-recordStart)/1000) + "s n=" + String(logCount));
  }
  display.display();

Show the status (RECORDING or READY), the big temperature in Celsius with one decimal, and — when recording — the temperature change and elapsed time. display.display() pushes everything to the screen.

The whole thing in one sentence

On power-on, connect to WiFi and register four web routes (setup). Then forever, answer phone requests, and every second read the temperature and — if recording is active — store it in the log and update the display (loop).

First thing to try: After uploading, open the IP in your phone browser. You should see the live temperature. Hold the DS18B20 probe between your fingers — your body temperature (about 37°C) should make the number climb in a few seconds, then fall back when you release it. This confirms the sensor is working before the experiment.

Check: The display should show temperature immediately. If it shows -127°C or 85°C, the sensor isn’t connected correctly or the pull-up resistor is missing.

Step 3: Run your trials

Protocol for each trial:

1. Open the web dashboard on your phone
2. Prepare beaker with correct water temperature (use kitchen thermometer to verify)
3. Put the DS18B20 probe in the water, wait for reading to stabilize (~30 seconds)
4. Tap “Start Recording”
5. Drop the Alka-Seltzer tablet immediately
6. Watch the temperature rise on the OLED
7. Wait 3–4 minutes until temperature returns to baseline
8. Tap “Stop Recording”
9. Download CSV and save it (rename: trial-cold.csv, trial-hot.csv, etc.)

Repeat for each condition. Each trial is about 5 minutes.

Analysis in Google Sheets:

• Plot all trials on one chart: time (X) vs. temperature (Y)
• Calculate: peak temperature rise (ΔT), time to peak, time to return to baseline
• Higher ΔT / faster peak = faster reaction rate

Presentation tip: Show all four curves on one graph with different colored lines. Point to where the hot water curve rises faster and peaks higher. Say: “The Arrhenius equation in chemistry predicts that a 10°C increase in temperature roughly doubles the reaction rate. My data shows [your result] — consistent with / different from the prediction because [reason].”

What just happened

The DS18B20 uses semiconductor physics to measure temperature. A diode junction voltage changes precisely with temperature. The chip converts this to a 12-bit digital value and sends it via the 1-Wire protocol — all in one tiny sensor.

Activation energy is the energy barrier a chemical reaction must overcome. Higher temperature = more molecules have enough kinetic energy to exceed the barrier = faster reaction. You just measured the Arrhenius relationship experimentally.

Curriculum connections:

• NGSS HS-PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs
• AP Chemistry: Reaction kinetics, Arrhenius equation, activation energy
• Common Core Math: Modeling with functions, rate of change

The shape of your temperature curve (sharp rise, slow decay) is an exponential decay curve — the same math as radioactive decay, Newton’s Law of Cooling, and RC circuits.

Level Up

Calculate rate quantitatively: In your spreadsheet, compute ΔTemp/Δtime for each second. This is the rate of temperature change — a proxy for reaction rate. Plot it. Find the maximum rate point.

Concentration effect: Keep temperature constant, vary tablet concentration (whole vs. half vs. quarter). Plot reaction rate vs. concentration.

Enzyme catalysis: Crush a pineapple and add the juice (contains bromelain enzyme) to your reaction. Does it speed up?

Troubleshooting