Lab 5: Sensors

2.12/2.120 Intro to Robotics
Spring 2024¹

Table of Contents

• 1 Microcontroller
  • 1.1 Validate Microcontroller
  • 1.2 Microcontroller Pinout
• 2 Wiring and Reading Sensors
  • 2.1 Potentiometer
    • 2.1.1 Wiring
    • 2.1.2 Coding
  • 2.2 Button
    • 2.2.1 Wiring
    • 2.2.2 Coding
  • 2.3 Time-of-Flight
    • 2.3.1 Wiring
    • 2.3.2 Coding
  • 2.4 IMU
    • 2.4.1 Wiring
    • 2.4.2 Coding
• 3 Sensor-controlled Motor
  • 3.1 Validate Motors
  • 3.2 Validate Encoders
  • 3.3 Sensor Integration
• 4 Free Exploration
• 4.1 Wireless Communication
  • 4.1.1 Wiring
  • 4.1.2 Coding
  • 4.1.3 Wireless Sensor-controlled Motor
• 4.2 TFT Display
  • 4.2.1 Wiring
  • 4.2.2 Coding
  • 4.2.3 Sensor Integration
• 5 Feedback Form

1 Microcontroller

Estimated time of completion: 5 min

1.1 Validate Microcontroller

Clone this repository and run robot/blink_test.cpp. You should see the onboard LED change colors!

Forget how to clone?

Please refer to the instructions from Lab 1.

1.2 Microcontroller Pinout

Refer to the pinout diagram here when choosing pins for sensors, motors, and encoders.

The pin numbers in code are usually defined either in include/pinout.h or through #define statements at the beginning of the test code. In this lab, you are free to use any pins as long as they are the right type and you update the code to match your chosen pins.

Feel free to clarify with staff if you are unsure what the labels mean! A printout of this diagram has also been provided to you.

2 Wiring and Reading Sensors

Estimated time of completion: 40 min

In this section, you will wire and code each sensor by following Adafruit tutorials. The instructions are intentionally vague to prepare you incase you use other sensors for the final project! Don't be afraid to ask the lab staff any questions you might have.

Please keep the sensors on the breadboard as you move through this section.

2.1 Potentiometer

2.1.1 Wiring

Wire the potentiometer onto your breadboard. Refer to this Adafruit page as an example.

2.1.2 Coding

Fill in test_sensors/pot_test.cpp with test code to read your potentiometer. Refer to this Adafruit page as an example.

Necessary changes:

• Add #include <Arduino.h> to the beginning of your file.

2.2 Button

2.2.1 Wiring

Wire the button, LED, and resistor onto your breadboard. Refer to this Adafruit page as an example. You only need one button.

2.2.2 Coding

Fill in test_sensors/button_test.cpp with test code to read your button. For this lab, we will be using the Bounce2 library to filter out undesired state changes (debouncing).

How do I import a library in PlatformIO?

1. Click the PIO Icon on the left side of the screen.

   

2. Go to PIO Home/Libraries.

   

3. Search for and click the Bounce2 library.

   

4. Click the "Add to Project" button. Don't click Add in the pop up! Instead, copy the text in the topmost textbox.

   

5. Exit out of the pop up by clicking the X or the "Cancel" button.

6. Navigate back to see your files and directories by clicking the topmost icon on the left side of the screen.

7. Open the platformio.ini file, likely the second to the last file, above README.md.

8. Paste the text you copied under the TODO, in the lib_deps section of [env].

9. Save the file. You should see PlatformIO reprocess the imported libraries.

Where do I find demo code?

1. Navigate back to the Bounce2 library.

2. You can select an example from the dropdown. For the button, we will use bounce_basic.

   

3. Copy the code into test_sensors/button_test.cpp.

2.3 Time-of-Flight

2.3.1 Wiring

Wire the ToF sensor onto your breadboard. We will be using the I2C protocol.

If you are using the VL6180X, refer to this Adafruit page as an example.

If you are using the VL53L0X, refer to this Adafruit page as an example.

2.3.2 Coding

Fill in test_sensors/tof_test.cpp with test code to read your time-of-flight sensor. Similar to the button, you will have to import the ToF library and refer to the demo code.

If you are using the VL6180X, refer to this Adafruit page as an example. The name of the library is Adafruit_VL6180X, and the demo code is called vl6180x.

If you are using the VL53L0X, refer to this Adafruit page as an example. The name of the library is Adafruit_VL53L0X, and the demo code is called vl53l0x.

2.4 IMU

2.4.1 Wiring

Wire the IMU onto your breadboard. Refer to this Adafruit page as an example. We will use the SPI protocol. SPI MISO is equivalent to SPI MI and SPI MOSI is equivalent to SPI MO.

2.4.2 Coding

Fill in test_sensors/imu_test.cpp with test code to read your IMU. We have already imported the IMU library for you. However, you will still have to look it up to refer to the demo code. The name of the library is Adafruit BNO08x, and the demo code is called quaternion_yaw_pitch_roll.

Necessary changes:

• Comment out line 17 #define BNO08X_RESET -1 and uncomment line 15 #define BNO08X_RESET 5
• Comment out line 52 if (!bno08x.begin_I2C()) { and uncomment line 54 if (!bno08x.begin_SPI(BNO08X_CS, BNO08X_INT)) {

3 Sensor-controlled Motor

Estimated time of completion: 15 min

3.1 Validate Motors

Push and hold either of the M1A and M1B buttons on the motor driver to see the wheel spin. Then, wire up the motor and run test_code/motor_drive_test.cpp. The wheel should spin in different directions with varied speeds.

3.2 Validate Encoders

Wire up the encoder and run test_code/encoder_test.cpp. Open the Serial Monitor and confirm that both the direction and the magnitude make sense.

3.3 Sensor Integration

We now want to use one of the sensors to dictate a variable involved in test_code/motor_position_control.cpp. For example, you can use the potentiometer reading to be setpoint. Running test_code/motor_position_control.cpp as is should make the motor oscillate back and forth.

Incorporate sensor reading code from the tests in the previous section into test_code/motor_position_control.cpp. You may have to map or convert your sensor reading into reasonable values for the variable you choose.

You are free to use any sensor you want. You can even use multiple sensors! Consider sensor/s that you think will be useful for the final project.

Getting an insanely large control effort??

If your control effort looks like it's 100 digits long, comment out any delay calls in the loop function. The delay might be messing with the timing of EVERY_N_MICROS.

✅ CHECKOFF 1 ✅
Demonstrate your new test_code/motor_position_control.cpp to a TA or LA.

4 Free Exploration

Estimated time of completion: now until the end of lab

The next two subsections are purposefully open-ended to encourage exploration. You are welcome to do either, both, or something completely different! (We have random sensors in the bin.) Again, consider doing something you think will be useful for the final project. You will demonstrate to the staff what you have made in the last 10-15 minutes of lab.

4.1 Wireless Communication

Upto now, we've only used wired communications. What happens if we want to control the mobile robot via joystick for the final project? Clearly, the joystick can't also be physically attached to the mobile robot. The microcontrollers we are using can communicate to each other via WiFi.

4.1.1 Wiring

You first need to divide your setup into a sender and a receiver. In our case, the sender should be connected to your chosen sensor, while the receiver should be connected to the motor. Ask the staff for any necessary parts and rewire your setup.

4.1.2 Coding

Run get_mac.cpp on the receiver to get the MAC address of the receiver microcontroller. Then, replace broadcastAddress in wireless/esp_now_sender.cpp to be that MAC address. Run wireless/esp_now_sender.cpp on the sender and wireless/esp_now_receiver.cpp on the receiver. Keep the receiver connected to your machine and open the Serial Monitor.

Confirm that the data received, as printed on the Serial Monitor, is reasonable given the data sent. Hint: Refer to lines 60 to 63 in wireless/esp_now_sender.cpp to see what data is being sent.

4.1.3 Wireless Sensor-controlled Motor

Copy wireless/esp_now_sender.cpp to lab_code/sensor_sender.cpp and wireless/esp_now_receiver.cpp to lab_code/robot_receiver.cpp.

Then, modify the newly copied code so that the sender reads and sends sensor data, while the receiver parses this data and uses it to command the motor. Remember what you learned in previous labs about structs to define a message type. You may need to incorporate code from test_code/motor_position/control.cpp.

If you get stuck, refer to this tutorial or ask the staff for help!

4.2 TFT Display

Up to now, we've conducted all our validation tests by printing to the Serial Monitor. This requires constant wired connection to your machine, which isn't always ideal. For example, you might want to troubleshoot sensors on your mobile robot as it is moving! In some cases, it is more convenient to instead use a TFT display.

4.2.1 Wiring

Ask the staff for a TFT display and wire it onto your breadboard using this Adafruit page as reference. If you did the wireless setup, wire the display to the sender. Or, if your breadboard is too crowded, ask the staff for another microcontroller and breadboard. Remember to validate the new microcontroller by first running robot/blink_test.cpp.

4.2.2 Coding

Import the Adafruit_HX8357 library and copy the example code into test_code/display_test.cpp. Run test_code/display_test.cpp to show text and shapes on your display.

4.2.3 Sensor Integration

Choose a sensor whose readings will be printed on the display. If you are using a new microcontroller and breadboard, rewire your chosen sensor on the new breadboard and revalidate it first using the test code you wrote in test_sensors/.

In lab_code/display_sensor.cpp, combine test_code/display_test.cpp and the test code you wrote in test_sensors/ to print sensor readings to the display instead of the Serial Monitor. You may find the implementation of testText() in test_code/display_test.cpp helpful.

✅ CHECKOFF 2 ✅
Show your chosen mini-project to a TA or LA.

5 Feedback Form

Before you leave, please fill out https://tinyurl.com/212-feedback.

✅ CHECKOFF 3 ✅
Show the feedback form completion screen to a TA or LA.

Footnotes

1. Version 1 - 2024: Joseph Ntaimo, Jinger Chong, Josh Sohn ↩