Week 9 Group Assignment: Using an Oscilloscope to Measure Grove Sensors

Task Overview

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

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

Testing Tutorial for XIAO ESP32C3 with Grove DHT11 Temperature and Humidity Sensor

I used the OWON EDS102CV oscilloscope, 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

Key Technical Specifications:

Bandwidth: 100MHz
Number of Channels: 2
Maximum Sampling Rate: 1GS/s
Time Base Range: 2ns/div - 100s/div
Vertical Sensitivity: 2mV/div - 10V/div
Display: 8-inch color LCD

For oscilloscope function details, refer to Katherine's document: Week12. Input Devices.

Introduction to Grove DHT11 Temperature and Humidity Sensor

The Grove DHT11 is a basic digital temperature and humidity sensor manufactured by Seeed Studio, designed for entry-level electronics projects. Below 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: Standard Grove interface design, no soldering required, plug-and-play
Low Power Consumption: Average operating current 0.5mA, standby current about 100μA
Small Size: Compact sensor module for easy integration into various projects
Signal Transmission Distance: Up to 20 meters under standard conditions
Long-term Stability: Calibration coefficients stored in OTP memory for stable operation

Working Principle

The DHT11 contains a resistive humidity sensing element and an NTC temperature sensing element. After collecting environmental data, the sensor outputs digital signals to the microcontroller via a single-bus protocol. A complete data transmission includes 40 bits of data, comprising the integer and decimal parts of humidity and temperature, as well as a checksum.

Communication Protocol

The DHT11 uses a simplified single-bus communication protocol:

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

Application Scenarios

Home Automation Projects: Indoor environment monitoring
Weather Stations: Simple weather monitoring
Educational Projects: Learning Arduino, Raspberry Pi, and other microcontrollers
Plant Care: Monitoring indoor plant growth environments
Simple Hygrometer/Thermometer: Combining with LCD/OLED displays

Advantages and Disadvantages

Advantages:

Cost-effective for beginners
Easy to use with rich code libraries
Grove interface facilitates rapid prototyping

Disadvantages:

Lower accuracy, unsuitable for high-precision requirements
Limited measurement range, unsuitable for extreme environments
Slow update rate, recommended measurement interval ≥2 seconds

This sensor is ideal for beginners learning input devices and sensor communication protocols, especially in educational settings 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
Connecting wires
USB data cable
Computer (with Arduino IDE installed)

Part 1: Hardware Connection

Connecting DHT11 to XIAO ESP32C3
- Connect the VCC pin of Grove DHT11 to the 3.3V of XIAO ESP32C3
- Connect the GND pin of Grove DHT11 to the GND of XIAO ESP32C3
- Connect the DATA pin of Grove DHT11 to digital pin 2 (D2) of XIAO ESP32C3

The wiring diagram is shown below.

Wiring diagram for XIAO ESP32C3 and Grove DHT11

Connecting the Oscilloscope Probe
- Connect the probe needle of CH1 of the oscilloscope to the DATA pin of DHT11
- Connect the ground clip of the oscilloscope probe to the ground of the circuit
Connecting XIAO ESP32C3 to the Computer
- Use the USB data cable to connect the XIAO ESP32C3 to the computer

After the devices are connected, it should look like the following.

Actual connection of devices

Part 2: Software Setup

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

// 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' (it's 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 (isFahrenheit = 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"));
}

Uploading Code
- Select the correct 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 should see sensor data in the Arduino serial monitor as shown in the figure below. Keep the sensor outputting data when measuring with the oscilloscope.

Ensure the Arduino IDE serial monitor always displays sensor data

Part 3: Oscilloscope Measurement

Configuring Oscilloscope Settings
- Turn on the OWON EDS102CV oscilloscope.
- Set the time base (Time/Div) to 2ms/div and start observing.
- Set the voltage scale (Volts/Div) to 1V/div.
- Ensure CH1 is selected and displayed.
Observing DHT11 Communication Signals
- Observe the waveform displayed on the oscilloscope
- The DHT11 uses a single-bus protocol, so you should see the following characteristics:
  - Start signal: Low level lasting at least 18ms, followed by high level for 80μs.
  - Data transmission: Each bit consists of 50μs low + 26-28μs high (for "0") or 50μs low + 70μs high (for "1").
Adjusting Oscilloscope Settings
- If the signal is unclear, try adjusting the trigger level.
- Use the oscilloscope's single (Single) button trigger function to capture the complete communication process. Once data is captured, the Run/Stop button in the upper left corner will turn red and pause, as shown in the figure below.

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

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

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

Part 4: Measurement and Analysis

Based on the oscilloscope report, the measured parameters are listed in the table below:

Parameter (Chinese Name)	Measured Value
Period (T)	93.095μs
Frequency (F)	10.74KHz
Average Value (V)	1.526V
Peak-to-Peak (Vp)	3.380V
RMS (Vk)	2.250V
Minimum Value (Mi)	-20.00mV
Bottom 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)	?
Cycle RMS (TR)	370.9mV
Working Cycle (WP)	20.0%
Maximum Value (Ma)	3.360V
Top Value (Vt)	3.320V
Amplitude (Va)	3.340V
Top Overshoot (Ps)	0.0%
Fall Time (FT)	less than10.000μs
Negative Pulse Width (NW)	80.000μs
Negative Duty Cycle (~D)	80.0%
Distortion (ND)	?
Cursor RMS (CR)	0.000mV
Phase (RP)	0.000rad

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

1. Communication Cycle Analysis

Using the single (Single) trigger mode of the OWON EDS102CV oscilloscope, we captured the complete DHT11 data transmission cycle:

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

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

2. Data Bit Characteristic Analysis

From the oscilloscope image, we can observe:

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

This duty cycle data is crucial as it shows that the DHT11 occupies about 20% of the time with high level and 80% with low level during data transmission, which matches the encoding method of the DHT11 communication protocol where the value of data bits is distinguished by the duration of the high level.

3. Voltage Characteristics Analysis

Average Voltage (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 stabilizes around 3.3V, matching the 3.3V logic level of the XIAO ESP32C3. The average voltage of 1.526V reflects the proportion of time that the low level state occupies.

4. Timing Characteristics Analysis

Rise Time (RT): less than10.000μs
Fall Time (FT): less than10.000μs
Positive Pulse Width (PW): 20.000μs
Negative Pulse Width (NW): 80.000μs

These timing parameters align with the DHT11 protocol specifications. Particularly, the ratio of positive pulse width (20μs) to negative pulse width (80μs) corresponds to the 20%:80% duty cycle.

Observations and Analysis

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

Experimental Report Conclusion

Hardware Connection Evaluation

The connection between XIAO ESP32C3 and Grove DHT11 is simple and effective. Using digital pin D2 as the data line is sufficient for stable communication. The oscilloscope connection did not significantly interfere with the signal, and the complete communication waveform was successfully captured.

Characteristics of DHT11 Communication Protocol

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

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

Application Scenario Analysis

Based on the observations, the DHT11 sensor is suitable for:

Non-high-precision environmental monitoring systems, such as home weather stations.
Demonstrations for educational purposes and learning the single-bus communication protocol.
Simple environmental control systems, such as greenhouse controls.
Environmental perception components in low-cost IoT devices.

Testing Tutorial for XIAO ESP32S3 with ADXL345L Three-axis Accelerometer

Seeed Studio Grove 3-Axis Digital Compass

Task Objectives

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

ADXL345L Technical Specifications

Core Parameters

Parameter	Specification Value
Communication Protocol	I2C/SPI (using I2C in this tutorial)
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. Wiring between XIAO ESP32S3 and ADXL345L

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	Ground of the circuit board

Connect ADXL345L with XIAO ESP32S3 and connect the logic analyzer

Software Implementation

1. Arduino Code Framework

#include less thanWire.h>
#include less thanADXL345.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 to low while SCL is high
Address Frame: 0x53 (7-bit address + R/W bit)
Register Write: Sends 0x32 register address
Data Read: Continuously reads 6 bytes of data (each byte followed by ACK)

ADXL345L Data Manual

2. Data Parsing Verification

The GAIN for the three axes obtained from the data manual is as follows

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 are consistent with the expected results.

Verification and display of calculation results

Experimental Report Conclusion

1. Protocol Verification Results

• The I2C timing complies with standard specifications, with a measured SCL clock frequency of 100kHz
• The register read sequence is identical to that in the data manual
• The data parsing algorithm is verified, with errors within ±0.005g

2. Engineering Application Suggestions

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

Task Overview​

Testing Tutorial for XIAO ESP32C3 with Grove DHT11 Temperature and Humidity Sensor​

Introduction to Grove DHT11 Temperature and Humidity Sensor​

Basic Specifications​

Features​

Working Principle​

Communication Protocol​

Application Scenarios​

Advantages and Disadvantages​

Materials Preparation​

Part 1: Hardware Connection​

Part 2: Software Setup​

Part 3: Oscilloscope Measurement​

Part 4: Measurement and Analysis​

1. Communication Cycle Analysis​

2. Data Bit Characteristic Analysis​

3. Voltage Characteristics Analysis​

4. Timing Characteristics Analysis​

Observations and Analysis​

Experimental Report Conclusion​

Hardware Connection Evaluation​

Characteristics of DHT11 Communication Protocol​

Application Scenario Analysis​

Testing Tutorial for XIAO ESP32S3 with ADXL345L Three-axis Accelerometer

Task Objectives​

ADXL345L Technical Specifications​

Core Parameters​

Register Function Description​

Hardware Connection Guide​

1. Wiring between XIAO ESP32S3 and ADXL345L​

2. Logic Analyzer Connection​

Software Implementation​

1. Arduino Code Framework​

Logic Analyzer Verification​

1. Typical I2C Communication Waveform​

2. Data Parsing Verification​

Experimental Report Conclusion​

1. Protocol Verification Results​

2. Engineering Application Suggestions​

Task Overview

Testing Tutorial for XIAO ESP32C3 with Grove DHT11 Temperature and Humidity Sensor

Introduction to Grove DHT11 Temperature and Humidity Sensor

Basic Specifications

Features

Working Principle

Communication Protocol

Application Scenarios

Advantages and Disadvantages

Materials Preparation

Part 1: Hardware Connection

Part 2: Software Setup

Part 3: Oscilloscope Measurement

Part 4: Measurement and Analysis

1. Communication Cycle Analysis

2. Data Bit Characteristic Analysis

3. Voltage Characteristics Analysis

4. Timing Characteristics Analysis

Observations and Analysis

Experimental Report Conclusion

Hardware Connection Evaluation

Characteristics of DHT11 Communication Protocol

Application Scenario Analysis

Task Objectives

ADXL345L Technical Specifications

Core Parameters

Register Function Description

Hardware Connection Guide

1. Wiring between XIAO ESP32S3 and ADXL345L

2. Logic Analyzer Connection

Software Implementation

1. Arduino Code Framework

Logic Analyzer Verification

1. Typical I2C Communication Waveform

2. Data Parsing Verification

Experimental Report Conclusion

1. Protocol Verification Results

2. Engineering Application Suggestions