Week 9 Group Assignment: Measuring Grove Sensors with an Oscilloscope

Task Overview

According to the requirements in the Week 9 course outline, our group needs to select input devices, measure their electrical signal characteristics using an oscilloscope, and analyze and understand their working principles. In this assignment, we will:

Test XIAO ESP32C3 with Grove DHT11 temperature and humidity sensor (written by Lei Feng)
Test XIAO ESP32S3 with ADXL345L three-axis accelerometer (written by Liu Hongtai)

XIAO ESP32C3 with Grove DHT11 Temperature and Humidity Sensor Tutorial

I used the OWON EDS102CV oscilloscope for measurements. This is a dual-channel digital storage oscilloscope with a sampling rate of up to 1GS/s and a bandwidth of 100MHz, suitable for measuring and analyzing various electronic signals.

OWON EDS102CV oscilloscope

Main Technical Specifications:

Bandwidth: 100MHz
Number of channels: 2
Maximum sampling rate: 1GS/s
Timebase range: 2ns/div - 100s/div
Vertical sensitivity: 2mV/div - 10V/div
Display: 8-inch color LCD

For oscilloscope function descriptions, refer to Katherine's documentation: Week12. Input Devices.

Grove DHT11 Temperature and Humidity Sensor Introduction

Grove DHT11 is a basic digital temperature and humidity sensor manufactured by Seeed Studio, designed for entry-level electronic projects. Here are its main features:

Basic Specifications

Measurement Range: Temperature 0-50°C, Humidity 20-90%RH
Accuracy: Temperature ±2°C, Humidity ±5%RH
Resolution: Temperature 1°C, Humidity 1%RH
Supply Voltage: 3.3V-5.5V
Data Output: Single-bus digital signal

Features

Grove Interface: Designed with standard Grove interface, no soldering required, plug and play
Low Power Consumption: Average operating current 0.5mA, standby current about 100μA
Small Size: Small sensor module size, easy to integrate into various projects
Signal Transmission Distance: Up to 20 meters under standard conditions
Long-term Stability: Calibration coefficients stored in OTP memory, ensuring long-term stable operation

Working Principle

The DHT11 contains a resistive humidity measurement element and an NTC temperature measurement element. After the sensor collects environmental data, it outputs digital signals to the microcontroller through a single-bus protocol. A complete data packet contains 40 bits of data, including humidity integer part, humidity decimal part, temperature integer part, temperature decimal part, and checksum.

Communication Protocol

DHT11 uses a simplified single-bus communication protocol:

Host Sends Start Signal: Pulls the data line low for at least 18ms, then pulls it high for 20-40μs
Sensor Response: Pulls the data line low for 80μs, then high for 80μs
Data Transmission: Each data bit starts with a 50μs low-level signal, followed by a high-level signal whose duration determines whether the data bit is "0" or "1"
- "0": High level lasts 26-28μs
- "1": High level lasts 70μs

Application Scenarios

Home Automation Projects: Indoor environment monitoring
Weather Stations: Simple weather monitoring
Educational Projects: Arduino, Raspberry Pi, and other microcontroller learning
Plant Care: Indoor plant growth environment monitoring
Simple Temperature and Humidity Display: Combined with LCD/OLED displays

Advantages and Disadvantages

Advantages:

Low cost, suitable for beginners
Easy to use, rich code libraries
Grove interface facilitates rapid prototyping

Disadvantages:

Relatively low accuracy, not suitable for high-precision scenarios
Limited measurement range, not suitable for extreme environments
Slow update rate, recommended measurement interval ≥2 seconds

This sensor is an ideal choice for beginners learning about input devices and sensor communication protocols, particularly suitable for educational environments like the MIT Fab Academy input devices course.

Materials Preparation

XIAO ESP32C3 development board
Grove DHT11 temperature and humidity sensor
OWON EDS102CV oscilloscope
Oscilloscope probe
Connection wires
USB data cable
Computer (with Arduino IDE installed)

Part One: Hardware Connection

Connect DHT11 to XIAO ESP32C3
- Connect Grove DHT11's VCC pin to XIAO ESP32C3's 3.3V
- Connect Grove DHT11's GND pin to XIAO ESP32C3's GND
- Connect Grove DHT11's DATA pin to XIAO ESP32C3's D2 (digital pin 2)

The wiring diagram is shown below.

Wiring diagram of XIAO ESP32C3 and Grove DHT11

Connect the Oscilloscope Probe
- Connect the oscilloscope CH1 probe's tip to DHT11's DATA pin
- Connect the oscilloscope CH1 probe's ground clip to the circuit's GND
Connect XIAO ESP32C3 to Computer
- Use a USB data cable to connect XIAO ESP32C3 to the computer

The connected devices are shown below.

Live image of the actual device connections

Part Two: Software Setup

Install Necessary Libraries
- Open Arduino IDE
- Go to "Tools" > "Manage Libraries"
- Search for and install "DHT sensor library" and "Adafruit Unified Sensor" libraries
- Search for and install "Seeed XIAO ESP32C3" board support (if not already installed)
Basic Code Writing
- Create a new Arduino sketch
- Copy the following code:

cpp

// Example testing sketch for various DHT humidity/temperature sensors
  // Written by ladyada, public domain
  
  // REQUIRES the following Arduino libraries:
  // - DHT Sensor Library: https://github.com/adafruit/DHT-sensor-library
  // - Adafruit Unified Sensor Lib: https://github.com/adafruit/Adafruit_Sensor
  
  #include "DHT.h"
  
  #define DHTPIN D2   // Digital pin connected to the DHT sensor
  
  #define DHTTYPE DHT11   // DHT 11
  
  DHT dht(DHTPIN, DHTTYPE);
  
  void setup() {
    Serial.begin(9600);
    Serial.println(F("DHTxx test!"));
  
    dht.begin();
  }
  
  void loop() {
    // Wait a few seconds between measurements.
    delay(2000);
  
    // Reading temperature or humidity takes about 250 milliseconds!
    // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
    float h = dht.readHumidity();
    // Read temperature as Celsius (the default)
    float t = dht.readTemperature();
    // Read temperature as Fahrenheit (isFahrenheit = true)
    float f = dht.readTemperature(true);
  
    // Check if any reads failed and exit early (to try again).
    if (isnan(h) || isnan(t) || isnan(f)) {
      Serial.println(F("Failed to read from DHT sensor!"));
      return;
    }
  
    // Compute heat index in Fahrenheit (the default)
    float hif = dht.computeHeatIndex(f, h);
    // Compute heat index in Celsius (isFahreheit = false)
    float hic = dht.computeHeatIndex(t, h, false);
  
    Serial.print(F("Humidity: "));
    Serial.print(h);
    Serial.print(F("%  Temperature: "));
    Serial.print(t);
    Serial.print(F("°C "));
    Serial.print(f);
    Serial.print(F("°F  Heat index: "));
    Serial.print(hic);
    Serial.print(F("°C "));
    Serial.print(hif);
    Serial.println(F("°F"));
  }

Upload Code
- Select the correct development board: "Tools" > "Board" > "Seeed Studio XIAO Series" > "Seeed Studio XIAO ESP32C3"
- Select the correct port: "Tools" > "Port" > Select the COM port connected to XIAO
- Click the upload button

If the hardware connection is normal, you can see the sensor data shown in the Arduino serial monitor below. Keep the sensor continuously outputting data while measuring with the oscilloscope.

Keep the Arduino IDE serial monitor always showing sensor output data

Part Three: Oscilloscope Measurement

Configure Oscilloscope Settings
- Turn on the OWON EDS102CV oscilloscope.
- Set the timebase (Time/Div) to 2ms/div to start observing.
- Set the voltage scale (Volts/Div) to 1V/div.
- Make sure CH1 is selected and displayed.
Observe DHT11 Communication Signal
- Observe the waveform displayed on the oscilloscope
- DHT11 uses a single-bus protocol, you should be able to see the following characteristics:
  - Start signal: Low level lasting at least 18ms, then high level for 80μs.
  - Data transmission: Each bit consists of 50μs low level + 26-28μs high level (representing "0") or 50μs low level + 70μs high level (representing "1").
Adjust Oscilloscope Settings
- If the signal is not clear, try adjusting the trigger level.
- Use the oscilloscope's Single button trigger function to capture the complete communication process. After successfully capturing the data, the Run/Stop button in the upper left corner will turn red and pause, as shown below.

Using the Single button on the right can automatically capture the Grove DHT11 data transmission cycle

Use the "Add Measurement > Snapshot All" function to measure a comprehensive report of the signal, as shown below.

The "Add Measurement > Snapshot All" function can obtain a comprehensive report of the signal

Part Four: Measurement and Analysis

Based on the report provided by the oscilloscope, here is a list of the measured parameters:

Parameter Name	Measured Value
Period (T)	93.095μs
Frequency (F)	10.74KHz
Average Value (V)	1.526V
Peak-to-Peak Value (Vp)	3.380V
RMS Value (Vk)	2.250V
Minimum Value (Mi)	-20.00mV
Base Value (Vb)	-20.00mV
Overshoot (Os)	1.2%
Rise Time (RT)	<10.000μs
Positive Pulse Width (PW)	20.000μs
Positive Duty Cycle (D)	20.0%
Delay (PD)	?
Period RMS (TR)	370.9mV
Working Period (WP)	20.0%
Maximum Value (Ma)	3.360V
Top Value (Vt)	3.320V
Amplitude (Va)	3.340V
Top Shoot (Ps)	0.0%
Fall Time (FT)	<10.000μs
Negative Pulse Width (NW)	80.000μs
Negative Duty Cycle (~D)	80.0%
Distortion (ND)	?
Common Mode RMS (CR)	0.000mV
Phase (RP)	0.000rad

These parameters comprehensively describe the electrical, temporal, and frequency characteristics of the DHT11 sensor communication signal, providing important basis for analyzing the data transmission protocol.

1. Communication Cycle Analysis

Through the OWON EDS102CV oscilloscope's Single trigger mode capture, we observed that a complete DHT11 data transmission cycle is:

Period (T): 93.095μs
Frequency (F): 10.74KHz

This indicates that the basic bit pulse cycle of the DHT11 sensor during data transmission is about 93μs, which is consistent with the typical value range of 80-100μs in the DHT11 specifications.

2. Data Bit Characteristic Analysis

From the oscilloscope image, we can observe:

Waveform Characteristics: Square wave signal, showing alternating high and low levels
Peak-to-Peak Value (Vp): 3.380V, indicating that the signal swings from near 0V to about 3.3V, consistent with the 3.3V supply logic level
Duty Cycle:
- Positive Duty Cycle (D): 20.0%
- Negative Duty Cycle (~D): 80.0%

This duty cycle data is very important, showing that the DHT11 uses high level for about 20% of the time and low level for about 80% of the time when transmitting data. This is consistent with the DHT11 communication protocol's encoding method for "0" and "1" - differentiating data bit values through different high-level durations.

3. Voltage Characteristic Analysis

Average Voltage Value (V): 1.526V
Maximum Value (Ma): 3.360V
Top Value (Vt): 3.320V
Peak Value (Vp): 3.380V

The voltage characteristics show that the high level is stable at around 3.3V, which matches the XIAO ESP32C3's 3.3V logic level. The average voltage is 1.526V, reflecting that the low-level state occupies a greater proportion of time.

4. Time Characteristic Analysis

Rise Time (RT): <10.000μs
Fall Time (FT): <10.000μs
Positive Pulse Width (PW): 20.000μs
Negative Pulse Width (NW): 80.000μs

These time parameters are consistent with the DHT11 protocol specifications. In particular, the positive pulse width of 20μs and negative pulse width of 80μs correspond exactly to the 20%:80% duty cycle ratio.

Observation Results and Analysis

Signal Integrity The observed waveform shows stable and clear signals without obvious noise interference or signal distortion, indicating good connections and normal sensor operation.
Protocol Characteristics The captured waveform clearly demonstrates the single-bus communication characteristics of the DHT11:
- Data is transmitted in the form of continuous pulse trains
- Each data bit starts with a fixed low level, followed by a variable length high level
- The overall timing is stable, with no obvious jitter
Bit Encoding Verification According to the DHT11 protocol, a "0" bit consists of 50μs low level + 26-28μs high level, and a "1" bit consists of 50μs low level + 70μs high level. From the oscilloscope measurement results, the negative pulse width (low level) is about 80μs, and the positive pulse width (high level) is about 20μs, indicating that we mainly captured data bits representing "0".

Experiment Report Conclusion

Hardware Connection Evaluation

The connection method between XIAO ESP32C3 and Grove DHT11 is simple and effective, using D2 pin as the data line is sufficient to achieve stable communication. The oscilloscope connection did not cause obvious interference to the signal and successfully captured the complete communication waveform.

DHT11 Communication Protocol Features

Through oscilloscope observation, we verified that the single-bus communication protocol used by DHT11 has the following features:

Signal level range is 0-3.3V, matching the microcontroller logic level.
Basic communication cycle is about 93μs, frequency is 10.74KHz.
Data encoding uses duty cycle encoding, distinguishing "0" and "1" through high-level duration.
The signal has good edge characteristics, with rise and fall times both less than 10μs.

Application Scenario Analysis

Based on the observation results, the DHT11 sensor is suitable for:

Non-high-precision environmental monitoring systems, such as home weather stations.
Education and learning demonstrations of single-bus communication protocols.
Simple environmental control systems, such as greenhouse control.
Environmental sensing components for low-cost IoT devices.

XIAO ESP32S3 with ADXL345L Three-Axis Accelerometer Test Tutorial

Seeed Studio Grove 3-Axis Digital Compass

Task Objectives

Establish I2C communication connection between XIAO ESP32S3 and ADXL345L
Capture I2C protocol communication waveforms using a logic analyzer
Parse the data from register 0x32 to obtain three-axis acceleration values

ADXL345L Technical Specifications

Core Parameters

Parameter	Specification
Communication Protocol	I2C/SPI (this tutorial uses I2C)
Measurement Range	±2g/±4g/±8g/±16g
Resolution (±2g)	4mg/LSB
Output Data Rate	0.1Hz - 3200Hz
Operating Voltage	2.0V - 3.6V
I2C Address	0x53 (SDO=GND)
Three-Axis Data Registers	0x32-0x37 (X/Y/Z LSB)

Register Function Description

• 0x32: X-axis data low byte (X0)
• 0x33: X-axis data high byte (X1)
• 0x34: Y-axis data low byte (Y0)
• 0x35: Y-axis data high byte (Y1)
• 0x36: Z-axis data low byte (Z0)
• 0x37: Z-axis data high byte (Z1)

Hardware Connection Guide

1. XIAO ESP32S3 and ADXL345L Wiring

ADXL345L Pin	XIAO ESP32S3 Pin
VCC	3.3V
GND	GND
SDA	D4 (I2C_SDA)
SCL	D5 (I2C_SCL)
SDO	GND (address 0x53)

2. Logic Analyzer Connection

Logic Analyzer Channel	Connection Point
CH0	SDA line (white wire)
CH1	SCL line (red wire)
GND	PCB GND

Connecting ADX345L with XIAO ESP32S3 and the logic analyzer

Software Implementation

1. Arduino Code Framework

cpp

#include <Wire.h>
#include <ADXL345.h>


ADXL345 adxl; //variable adxl is an instance of the ADXL345 library

void setup() {
    Serial.begin(9600);
    adxl.powerOn();

    //set activity/ inactivity thresholds (0-255)
    adxl.setActivityThreshold(75); //62.5mg per increment
    adxl.setInactivityThreshold(75); //62.5mg per increment
    adxl.setTimeInactivity(10); // how many seconds of no activity is inactive?

    //look of activity movement on this axes - 1 == on; 0 == off
    adxl.setActivityX(1);
    adxl.setActivityY(1);
    adxl.setActivityZ(1);

    //look of inactivity movement on this axes - 1 == on; 0 == off
    adxl.setInactivityX(1);
    adxl.setInactivityY(1);
    adxl.setInactivityZ(1);

    //look of tap movement on this axes - 1 == on; 0 == off
    adxl.setTapDetectionOnX(0);
    adxl.setTapDetectionOnY(0);
    adxl.setTapDetectionOnZ(1);

    //set values for what is a tap, and what is a double tap (0-255)
    adxl.setTapThreshold(50); //62.5mg per increment
    adxl.setTapDuration(15); //625us per increment
    adxl.setDoubleTapLatency(80); //1.25ms per increment
    adxl.setDoubleTapWindow(200); //1.25ms per increment

    //set values for what is considered freefall (0-255)
    adxl.setFreeFallThreshold(7); //(5 - 9) recommended - 62.5mg per increment
    adxl.setFreeFallDuration(45); //(20 - 70) recommended - 5ms per increment

    //setting all interrupts to take place on int pin 1
    //I had issues with int pin 2, was unable to reset it
    adxl.setInterruptMapping(ADXL345_INT_SINGLE_TAP_BIT,   ADXL345_INT1_PIN);
    adxl.setInterruptMapping(ADXL345_INT_DOUBLE_TAP_BIT,   ADXL345_INT1_PIN);
    adxl.setInterruptMapping(ADXL345_INT_FREE_FALL_BIT,    ADXL345_INT1_PIN);
    adxl.setInterruptMapping(ADXL345_INT_ACTIVITY_BIT,     ADXL345_INT1_PIN);
    adxl.setInterruptMapping(ADXL345_INT_INACTIVITY_BIT,   ADXL345_INT1_PIN);

    //register interrupt actions - 1 == on; 0 == off
    adxl.setInterrupt(ADXL345_INT_SINGLE_TAP_BIT, 1);
    adxl.setInterrupt(ADXL345_INT_DOUBLE_TAP_BIT, 1);
    adxl.setInterrupt(ADXL345_INT_FREE_FALL_BIT,  1);
    adxl.setInterrupt(ADXL345_INT_ACTIVITY_BIT,   1);
    adxl.setInterrupt(ADXL345_INT_INACTIVITY_BIT, 1);
}

void loop() {

    //Boring accelerometer stuff
    int x, y, z;
    adxl.readXYZ(&x, &y, &z); //read the accelerometer values and store them in variables  x,y,z
    // Output x,y,z values
    Serial.print("values of X , Y , Z: ");
    Serial.print(x);
    Serial.print(" , ");
    Serial.print(y);
    Serial.print(" , ");
    Serial.println(z);

    double xyz[3];
    double ax, ay, az;
    adxl.getAcceleration(xyz);
    ax = xyz[0];
    ay = xyz[1];
    az = xyz[2];
    Serial.print("X=");
    Serial.print(ax);
    Serial.println(" g");
    Serial.print("Y=");
    Serial.print(ay);
    Serial.println(" g");
    Serial.print("Z=");
    Serial.print(az);
    Serial.println(" g");
    Serial.println("**********************");
    delay(500);

}

Logic Analyzer Verification

1. Typical I2C Communication Waveform

Capturing logic data when reading three-axis data

Waveform Feature Analysis:

Start Condition: SDA transitions from high→low while SCL is high
Address Frame: 0x53 (7-bit address + R/W bit)
Register Write: Send register address 0x32
Data Read: Continuously read 6 bytes of data (each byte followed by ACK)

ADXL345L datasheet

2. Data Parsing Verification

From the datasheet, the GAIN values for the three axes are:

X: 0.00376390
Y: 0.00376009
Z: 0.00349265

Register Address	Raw Value (HEX)	Calculation	Actual Acceleration (g)
0x32 (X0)	0x34	52 * 0.00376390	+0.1957228g
0x33 (X1)	0x00
0x34 (Y0)	0x05	-251 * 0.00376009	-0.94378259g
0x35 (Y1)	0xFF
0x36 (Z0)	0x43	67 * 0.00349265	+0.23400755g
0x35 (Z1)	0x00

The actual reading results match the expectations

Verification and display of calculation results

Experiment Report Conclusion

1. Protocol Verification Results

• I2C timing conforms to standard specifications, measured SCL clock frequency is 100kHz
• Register read sequence is completely consistent with the datasheet
• Data parsing algorithm verification passed, error range within ±0.005g

2. Engineering Application Suggestions

• Motion Detection: Implement fall detection using threshold interrupt functionality
• Posture Recognition: Calculate device tilt angle using three-axis data
• Low Power Optimization: Adjust output data rate to reduce power consumption

Week 9 Group Assignment: Measuring Grove Sensors with an Oscilloscope ​

Task Overview ​

XIAO ESP32C3 with Grove DHT11 Temperature and Humidity Sensor Tutorial ​

Grove DHT11 Temperature and Humidity Sensor Introduction ​

Basic Specifications ​

Features ​

Working Principle ​

Communication Protocol ​

Application Scenarios ​

Advantages and Disadvantages ​

Materials Preparation ​

Part One: Hardware Connection ​

Part Two: Software Setup ​

Part Three: Oscilloscope Measurement ​

Part Four: Measurement and Analysis ​

1. Communication Cycle Analysis ​

2. Data Bit Characteristic Analysis ​

3. Voltage Characteristic Analysis ​

4. Time Characteristic Analysis ​

Observation Results and Analysis ​

Experiment Report Conclusion ​

Hardware Connection Evaluation ​

DHT11 Communication Protocol Features ​

Application Scenario Analysis ​

XIAO ESP32S3 with ADXL345L Three-Axis Accelerometer Test Tutorial ​

Task Objectives ​

ADXL345L Technical Specifications ​

Core Parameters ​

Register Function Description ​

Hardware Connection Guide ​

1. XIAO ESP32S3 and ADXL345L Wiring ​

2. Logic Analyzer Connection ​

Software Implementation ​

1. Arduino Code Framework ​

Logic Analyzer Verification ​

1. Typical I2C Communication Waveform ​

2. Data Parsing Verification ​

Experiment Report Conclusion ​

1. Protocol Verification Results ​

2. Engineering Application Suggestions ​

Week 9 Group Assignment: Measuring Grove Sensors with an Oscilloscope

Task Overview

XIAO ESP32C3 with Grove DHT11 Temperature and Humidity Sensor Tutorial

Grove DHT11 Temperature and Humidity Sensor Introduction

Basic Specifications

Features

Working Principle

Communication Protocol

Application Scenarios

Advantages and Disadvantages

Materials Preparation

Part One: Hardware Connection

Part Two: Software Setup

Part Three: Oscilloscope Measurement

Part Four: Measurement and Analysis

1. Communication Cycle Analysis

2. Data Bit Characteristic Analysis

3. Voltage Characteristic Analysis

4. Time Characteristic Analysis

Observation Results and Analysis

Experiment Report Conclusion

Hardware Connection Evaluation

DHT11 Communication Protocol Features

Application Scenario Analysis

XIAO ESP32S3 with ADXL345L Three-Axis Accelerometer Test Tutorial

Task Objectives

ADXL345L Technical Specifications

Core Parameters

Register Function Description

Hardware Connection Guide

1. XIAO ESP32S3 and ADXL345L Wiring

2. Logic Analyzer Connection

Software Implementation

1. Arduino Code Framework

Logic Analyzer Verification

1. Typical I2C Communication Waveform

2. Data Parsing Verification

Experiment Report Conclusion

1. Protocol Verification Results

2. Engineering Application Suggestions