Abstract
Mechanical switches are common in many machines and robots. They can be used to detect when a button is pushed, when a door is open, or a low-speed collision when two objects bump into each other. Switches can act as "bump sensors" on a simple robot to help it detect when it hits an obstacle. The robot can use this information to navigate around obstacles and avoid getting stuck. Can you build and program a robot that can drive around your house while using bump sensors to avoid obstacles?Summary
Recommended Project Supplies
Objective
Build and program an autonomous robot that navigates using bump sensors.Introduction
Advanced autonomous robots like the Perseverance rover (Figure 1) use a variety of cameras to detect obstacles and navigate around them. Since the robot is millions of miles from Earth, scientists will be unable to fix it if it crashes or gets stuck. In this case, it is very important to detect obstacles before the robot bumps into them.
Figure 1. The Perseverance rover.
Simpler robots, like the iRobot® Roomba®, an autonomous vacuum cleaner robot (Figure 2), commonly use bump sensors to detect obstacles. For example, bump sensors can be used to detect low-speed collisions between the robot and a piece of furniture. Newer, faster moving versions of the Roomba use forward-facing infrared sensors to detect objects and slow the robot down before the bump sensor hits them. When the robot hits an obstacle, its programming tells it to back up or turn around. This allows the robot to drive around a room without getting stuck against a wall or piece of furniture, even though it does not start out with a pre-planned path or a map of the entire room.
Figure 2. A Roomba® robotic vacuum cleaner. (Source: Larry D. Moore, CC BY-SA 3.0, Wikimedia Commons.)
In this project, you will build a robot that behaves like a Roomba®. It will have two bump sensors that you can mount on the robot. Can you design a program that will allow the robot to drive around without getting stuck?
Terms and Concepts
Questions
- What are the advantages and disadvantages of a robot using cameras vs. bump sensors to navigate?
Bibliography
General electronics references:
- Science Buddies (n.d.). How to Use a Breadboard. Retrieved July 6, 2020.
- Science Buddies (n.d.). How to Use a Multimeter. Retrieved July 6, 2020.
- Science Buddies (n.d.). Wire Stripping Tutorial. Retrieved July 6, 2020.
References for using an Arduino:
- Science Buddies (n.d.). How to Use an Arduino. Retrieved July 6, 2020.
- Arduino (n.d.). Language Reference. Retrieved July 6, 2020.
Reference about the cameras on the Mars 2020 Perseverance rover:
- NASA (n.d.). The Cameras on the Mars 2020 Perseverance Rover. Retrieved July 10, 2020.
References about the Roomba's sensors:
- iRobot (n.d.). Why is my Roomba® Bumping into Obstacles Harder than before?. Retrieved July 10, 2020.
- Layton, J. (n.d.). How Robotic Vacuums Work. HowStuffWorks. Retrieved July 10, 2020.
Datasheet for the L293D H-bridge motor driver:
- Texas Instruments (January 2016). L293x Quadruple Half-H Drivers. Retrieved July 8, 2020.
Materials and Equipment 
Recommended Project Supplies
Notes about using an Arduino:
- The list below shows all the individual parts you need to purchase to do this project. An Arduino starter kit, like the Elegoo UNO Super Starter Kit, may be worth it if you plan to do more Arduino projects in the future. They contain many of the parts you will need for this and other projects. If you decide to purchase a starter kit, make sure you check this project's materials list for other parts you might still need to purchase separately. Note that since the Arduino project is open source, some starter kits contain third-party Arduino-compatible boards with equivalent functionality.
- You have several options when it comes to programming your Arduino. You can install the Arduino Integrated Development Environment (IDE) locally on your computer by following the instructions for your operating system on the Arduino software page. Alternatively, you can use the web-based editor, which offers cloud storage of your programs so you can access them from multiple computers. If you have a Chromebook, see the Arduino Chrome App page for instructions.
- This project was developed with the Arduino UNO R3. The Arduino UNO R4 is now available, and was designed for backwards compatibility with UNO R3 projects. However, some third-party Arduino libraries may not work with the UNO R4. You can learn more about the UNO R4 on the official Arduino website.
- You will need a USB cable to upload code from your computer to your Arduino. The type of cable you need depends on what type of USB ports your computer has and which version of the Arduino you have. Make sure you purchase a USB cable or adapter that is compatible with your computer and your Arduino.
- Bluebot 4-in-1 robotics kit. The kit includes a robot chassis, wheels, motors, breadboard, batteries, and circuit parts to build four different robots.
- An Arduino Uno
- A 9V battery snap connector with barrel jack connector
- 9V battery
- A USB-B printer cable to connect your Arduino to a computer and program it
- Computer with free Arduino software installed (you can also use Arduino's web-based editor)
- Some additional tools are recommended for working with circuits:
- A digital multimeter is strongly recommended for help with troubleshooting
- Alligator clip leads make it easier to connect your multimeter probes to your circuit
- Needle nose pliers or tweezers make it easier to handle small parts
- Wire strippers allow you to cut wires to custom lengths, keeping your circuit neater
- Double-sided foam tape
- Lab notebook
Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.
Experimental Procedure
- Assemble your Bluebot chassis as shown in this video. However, instead of mounting the 4xAA battery pack on top of the robot, mount it on the lower plate. Then mount your Arduino next to the breadboard on the top plate.
- To control your robot's motors, you will use the L293D H-bridge motor driver chip, included in your BlueBot kit. This chip allows you to control the speed and direction of two motors. Figure 3 shows the pinout from the chip's datasheet and Table 1 describes the functions of the pins. When one of the input pins ("A") for a motor is high and the other one is low, the motor will spin. Reversing which pin is high/low reverses the motor's direction (Table 2). If both input pins are high or both input pins are low, the motor will stop. Do not worry if that does not make sense yet. You will wire the circuit and see example code in the next few steps.
Pinout for the L293D H-bridge chip. Pins are in two columns of 8, labeled one through 16, counter-clockwise from the top left, as follows: 1,2EN 1A 1Y 'HEAT SINK AND GROUND' 'HEAT SINK AND GROUND' 2Y 2A VCC2 3,4EN 3A 3Y 'HEAT SINK AND GROUND' 'HEAT SINK AND GROUND' 4Y 4A VCC1
Figure 3. L293D H-bridge chip pinout.
| Name | Pin number(s) | Description |
|---|---|---|
| VCC1 | 16 | Digital logic voltage supply (5V from Arduino) |
| VCC2 | 8 | Motor power voltage supply (6V from 4xAA battery pack) |
| GROUND | 4, 5, 12, 13 | Electrical ground |
| 1,2EN | 1 | Speed control for motor 1 using pulse width modulation (PWM) signal from Arduino |
| 3,4EN | 9 | Speed control for motor 2 using pulse width modulation (PWM) signal from Arduino |
| 1A, 2A | 2, 7 | Inputs to control motor 1 using Arduino digital pins |
| 3A, 4A | 10, 15 | Inputs to control motor 2 using Arduino digital pins |
| 1Y, 2Y | 3, 6 | Outputs to drive motor 1 |
| 3Y, 4Y | 11, 14 | Outputs to drive motor 2 |
| 1A | 2A | Motor 1 behavior |
|---|---|---|
| Low | Low | Stop |
| Low | High | Spin |
| High | Low | Spin the other way |
| High | High | Stop |
- Before you worry about connecting the bump sensors, you should make sure your robot's motors work and that it can drive around. Connect your motors, batteries, and the L293D, as shown in Figure 4 (note: there is more than one correct way to wire the circuit, this is just an example). The colors shown in the picture are for readability purposes only; your wire colors do not need to match. If you are not sure how to wire a circuit on a breadboard, see the How to Use a Breadboard resource. Here are a few things to look out for when building the circuit:
- Make sure the L293D is oriented with the notch facing "up" on the breadboard.
- Important: All the components in your circuit should have a "common ground." This means the Arduino's ground pin, the L293D's ground pins, and the 4xAA battery pack's negative wire should all be connected to the ground bus on the breadboard, and the ground buses on opposite sides of the breadboard should be connected.
- However, make sure you do not short-circuit the 5V Arduino supply to the 6V battery supply. In the diagram, notice how the left and right power buses on the breadboard are not connected with a jumper wire. The left-side bus provides 6V from the battery pack, and the right-side bus provides 5V from the Arduino. The H-bridge makes use of both power supplies: one for internal logic (5V from the Arduino) and one to power the motors (6V from the batteries). The external 4xAA battery pack is required because the Arduino cannot provide enough current to drive the motors directly.
Circuit diagram with the following connections: 9V battery to Arduino barrel jack; Arduino 5V pin to breadboard right-side power bus; Arduino GND pin to breadboard ground bus; 4xAA battery pack positive wire to breadboard A1; 4xAA battery pack ground wire to breadboard ground bus; Jumper wire connecting breadboard left and right ground buses; Do NOT connect the breadboard left and right power buses, this will short the Arduino 5V supply to the 6V from the battery pack; Power switch in breadboard C1, C2, C3; Jumper wire from left side power bus to A2; L293D chip straddling middle gap in breadboard from rows 10-17, with notch facing up (towards row 1); Jumper wire from breadboard A10 to Arduino pin 10; Jumper wire from breadboard B11 to Arduino pin 9; Motor negative lead to breadboard A12; Jumper wire from breadboard A13 to ground bus; Jumper wire from breadboard A14 to ground bus; Motor positive lead to breadboard A15; Jumper wire from breadboard C16 to Arduino pin 8; Jumper wire from breadboard A17 to left side power bus; Jumper wire from breadboard J10 to right side power bus; Jumper wire from breadboard G11 to Arduino pin 13; Motor negative lead to breadboard J12; Jumper wire from breadboard J13 to ground bus; Jumper wire from breadboard J14 to ground bus; Motor positive lead to breadboard J15; Jumper wire from breadboard H16 to Arduino pin 12; Jumper wire from breadboard H17 to Arduino pin 11;
Figure 4. Wiring diagram for connecting the Arduino to the L293D, your robot's motors, and batteries. A bigger version of the image is available.
- Make sure the power switch for the 4xAA battery pack is off and that the barrel jack for the 9V battery is unplugged (always do this before connecting the USB cable to program your Arduino). Enter the code shown in Figure 5 and upload it to your Arduino. If you are unsure how to do this, refer to the How to Use an Arduino guide.
// declare variables for motor control pins int Motor1Speed = 10; int Motor1Control1 = 9; int Motor1Control2 = 8; int Motor2Speed = 11; int Motor2Control1 = 13; int Motor2Control2 = 12; // declare variable for motor speed (0-255) int speed = 255; // declare variable for delay time in milliseconds int delayTime = 1000; void setup() { // setup code that only runs once // set motor control pins as outputs pinMode(Motor1Speed, OUTPUT); pinMode(Motor1Control1, OUTPUT); pinMode(Motor1Control2, OUTPUT); pinMode(Motor2Speed, OUTPUT); pinMode(Motor2Control1, OUTPUT); pinMode(Motor2Control2, OUTPUT); // set speed for both motors analogWrite(Motor1Speed, speed); analogWrite(Motor2Speed, speed); } void loop() { // code that loops forever // set both wheels to spin forward for delayTime milliseconds digitalWrite(Motor1Control1, HIGH); digitalWrite(Motor1Control2, LOW); digitalWrite(Motor2Control1, HIGH); digitalWrite(Motor2Control2, LOW); delay(delayTime); // stop for delayTime milliseconds digitalWrite(Motor1Control1, LOW); digitalWrite(Motor1Control2, LOW); digitalWrite(Motor2Control1, LOW); digitalWrite(Motor2Control2, LOW); delay(delayTime); }
Figure 5. Example code to control the robot's motors using the H-bridge.
- Put your robot on the ground and turn the power switch on. If everything is working correctly, the robot should repeatedly drive forward for one second, then pause for one second. If it does not, here are some common troubleshooting steps:
- Instead of changing your code, you can just switch the red and black wires for a motor to change the direction it spins. You can do this if your robot goes backwards or spins in circles instead of driving forward.
- If your motors do not spin at all, double-check all of your wiring. If your H-bridge is not wired properly, your motors will not spin.
- If your motors still do not spin, use a multimeter to debug your circuit. Refer to the How to Use a Multimeter guide if needed. Try the following:
- Make sure you have 5V coming from the Arduino.
- Make sure you have 6V coming from the 4xAA battery pack.
- Measure the voltages on the Arduino output pins to make sure they are what you expect (for example, based on the code, pin 9 should toggle between 5V and 0V).
- To confirm that your motors work, disconnect them from the H-bridge and connect them directly to 6V and ground on the breadboard.
- To confirm that your H-bridge works, disconnect it from the Arduino's digital pins. Use jumper wires to manually connect the H-bridge's input pins to 5V or 0V on the breadboard. (Make sure you reconnect the motors to the H-bridge first.)
- Practice steering your robot. Can you modify the program in Figure 5 to make your robot drive in a square? This is called "open loop" navigation, or "dead reckoning." The robot is hard-coded to follow a pre-determined path, without responding to any sensor input. This type of navigation is generally not a good idea, because small errors will accumulate over time, and eventually the robot will drift off course. However, it is a good way to practice programming and make sure your circuit works.
- Now it is time to connect a bump sensor. The bump sensor is a switch with three pins. Look closely at the sensor and you will see the labels "N.C.," "N.O.," and "C." These stand for Normally Closed, Normally Open, and Common, respectively. This means that when the switch is not pressed, the connection between the N.C. and C pins is closed, and the connection between the N.O. and C. pins is open. When the switch is pressed, the connections are reversed. This means that you can use the switch to toggle an Arduino digital pin between 0V and 5V.
- Connect a bump sensor to your Arduino, as shown in Figure 6. Note that the H-bridge, motors, and batteries are omitted from this diagram to avoid clutter, but you can leave them connected in your circuit.
- Important: Note that the sensor's white wire is connected to 5V and the red wire is connected to the Arduino's digital pin. This goes against the usual convention that red wires are used for the positive power bus connection. It is important to wire the sensor correctly in order to avoid shorting the Arduino's 5V supply to ground.
Long alt text: bump sensor, viewed with the metal lever facing up and to the right. When viewed in this orientation, from top to bottom, the sensor's pins are connected to breadboard ground, 5V, and Arduino pin 7 respectively.
Figure 6. Bump sensor connected to an Arduino digital pin. The common pin is connected to an Arduino digital pin. The Normally Open and Normally Closed pins are connected to 5V and ground, respectively. This way, the digital input pin will read 0V when the switch is not pressed, and 5V when the switch is pressed.
- Start a new Arduino sketch and enter the code shown in Figure 7.
int sensorPin = 7; // declare variable for sensor input pin int pinState; // declare variable for sensor state void setup() { // setup code that only runs once pinMode(sensorPin, INPUT); // set the sensor pin as an input Serial.begin(9600); // initialize serial communication } void loop() { // code that loops forever pinState = digitalRead(sensorPin); if (pinState == true){ Serial.println('Switch pressed'); }else{ Serial.println('witch not pressed'); } }
Figure 7. Example code to detect when the bump sensor is pressed using the Arduino's digital input.
- Upload the code to your Arduino, and leave the Arduino plugged into the USB cable. Select Tools→Serial Monitor from the top menu in your Arduino window. Make sure you select 9600 baud from the drop-down menu in the lower right. This will give you a window that prints a message indicating whether or not the switch is pressed (Figure 8).
- If the message displayed in your serial monitor does not change when you press the switch, double-check your wiring. Use a multimeter to confirm that the voltage on the Arduino's input pin changes between 0V and 5V when you press the switch. If it does not, your switch is wired incorrectly.
Figure 8. The Arduino serial monitor displaying messages to indicate whether or not the switch is pressed.
- You now have all the pieces that you need to build an autonomous robot that navigates with bump sensors! Can you program your robot to navigate based on readings from one or more bump sensors? For example, try programming these different behaviors (see the next step for hints). Which behavior do you think would be best for a robot that needs to drive around a room without getting stuck?
- Put one bump sensor on the front of the robot and one sensor on the back. Make the robot change direction whenever it bumps into something.
- Put both bump sensors on the front of the robot, one on the left and one on the right (Figure 9). Make the robot turn left or right when it hits an obstacle.
- Make the robot back up first, then turn when it hits an obstacle.
Figure 9. Robot with two bump sensors mounted on the front.
- Depending on your level of programming experience, you may need to read more in the Arduino Language Reference. You can also ask for help in the Science Buddies Ask an Expert forums. Here are some hints and suggestions:
- It is bad practice to repeatedly copy and paste the same lines or sections of code. If you find yourself doing so, it is better to put that code in a function. It may be useful to make functions for basic robot movements like "driveForward" or "turnRight." Can you simplify the code you wrote to make your robot drive in a square using functions?
- "IF/ELSE" statements allow your program to perform different actions depending on whether or not certain conditions are true (for example, if a variable is above or below a certain value). What happens when you make your robot's motion depend on the sensor input, instead of hard-coding a certain behavior?
- You can change the motors' speed using the analogWrite() command (see Figure 7). In the example program, the motors are set to "full speed," or 255. It might be easier to control your robot if it is not going full speed at all times.
Ask an Expert
Global Connections
This project explores topics key to Industry, Innovation and Infrastructure: Build resilient infrastructure, promote sustainable industrialization and foster innovation.
Variations
- You can purchase additional bump sensors, usually called lever switches, individually. What happens if you add more bump sensors to your robot? For example, put two on the front and two on the back.
- What are the results when you use the other sensors in your BlueBot kit to program other navigation behaviors for your robot? See this autonomous robot project idea for ideas.
Careers
If you like this project, you might enjoy exploring these related careers:
Contact Us
If you have purchased a kit for this project from Science Buddies, we are pleased to answer your questions.In your email, please follow these instructions:
- What is your Science Buddies kit order number?
- Please describe how you need help as thoroughly as possible:
Examples
Good Question I'm trying to do Experimental Procedure step #5, "Scrape the insulation from the wire. . ." How do I know when I've scraped enough?
Good Question I'm at Experimental Procedure step #7, "Move the magnet back and forth . . ." and the LED is not lighting up.
Bad Question I don't understand the instructions. Help!
Good Question I am purchasing my materials. Can I substitute a 1N34 diode for the 1N25 diode called for in the material list?
Bad Question Can I use a different part?
Contact Us
Related Links
- Science Fair Project Guide
- Other Ideas Like This
- Robotics Project Ideas
- Space Exploration Project Ideas
- My Favorites
