3.2Micro:bit Greeting Robot Projects

1. Projects

Click to download codes.

1.1 Servo

A servo is a kind of position driver, which is mainly composed of housing, circuit board, core-less motor, gear and position detector. The receiver or microcontroller sends a signal to the servo which has an internal reference circuit that generates a reference signal with a period of 20ms and a width of 1.5ms, and compares the DC bias voltage with the voltage of the potentiometer to output voltage difference.

There are many specifications of servos, yet all contains three colors of wires: brown, red and orange. Brown is the grounded, red is the positive, and orange is signal. The wire colors may vary from brands.

The rotation Angle of the servo is controlled by adjusting the duty cycle of the PWM (pulse width modulation) signals. Theoretically, the period of the standard PWM signal is fixed at 20ms (50Hz), so the pulse width should be 1ms ~ 2ms. But in fact, it is 0.5ms ~ 2.5ms, corresponding to the servo angle of 0° ~ 180°.

1.1.1 Parameters

Operating voltage: DC 3.3 ~ 5V

Operating Angle range: approx. 180°(at 500→2500 μsec)

Pulse width: 500→2500 μsec

No load speed: 0.12± 0.01sec /60 (DC 4.8V) 0.1± 0.01sec /60 (DC 6V)

No load current: 200±20mA (DC 4.8V) 220±20mA (DC 6V)

Stopping torque: 1.3±0.01kg·cm (DC 4.8V) 1.5±0.1kg·cm (DC 6V)

Stop current: ≦850mA (DC 4.8V) ≦1000mA (DC 6V)

Standby current: 3±1mA (DC 4.8V) 4±1mA (DC 6V)

1.1.2 Wiring Diagram

Expansion board

Servo A

GND

G (brown)

3V3

V (red)

P1 / io14

S (yellow)

1.1.3 Test Code

ATTENTION: The servo is able to rotate from 0 to 180 degrees. Yet after assembly, it can only move within 0-90 degrees. Otherwise, it may burn out due to stuck and overheating.

Click to download codes.

Build code blocks manually:

1. Click to load the library of servo.

2. Search “Servo” and you will see the Servo library. Click to load it.

3. Successfully loaded.

4. In , put into , and set pin to P0, angle to 0 degree.

5. In , put under , and set the delay to 1000ms.

6. Repeat step 4 and 5, but set the angle to 60 degree and 90 degree.

Complete code:

1.1.4 Test Result

The arm of the greeting robot moves.

1.2 Waving Arm

We combine two servos to make the robot to do some actions.

1.2.1 Test Code: Left-turn

1. In , put into , and set the pin to P0, angle to 0 degree.

2. In , put and into , and set the pin to P1, angle to 0 degree.

3. Repeatedly, but set P1 to 90°.

1.2.2 Result

The palm of the greeting robot turns left.

1.2.3 Test Code: Greeting

1. In , put into , and set the pin to P0, angle to 90.

2. In , put and into , and set the pin to P1, angle to 0 degree.

3. Repeatedly, but set P1 to 90°.

1.2.4 Result

The robot put its arms up and wave for welcome.

1.3 Ultrasonic

Before learning: In this project, we introduce the fundamentals of ultrasound. We will use the ultrasonic sensor to print detected distances on the serial monitor.

1.3.1 Overview

Like bats, HC-SR04 ultrasonic sensor uses sonar to determine the distance to an object. It provides excellent contact-less range inspection with high accuracy and stable readings. It is also equipped with ultrasonic transmitter and receiver. It is widely applied to electronics projects for obstacle detection and distance measurement.

1.3.2 Module Parameters

1.3.3 Wiring Diagram

Expansion board

Ultrasonic sensor

3V3

VCC

TRIG

P12/io15

ECHO

P8/io4

GND

GND

1.3.4 Test Code

Add an Extension.

Search “sonar” and click to load it.

Make a variable.

Set a serial port.

Initialize the serial port.

Initialize the ultrasonic sensor, and assign the ultrasonic sensor value to the variable.

Print the ultrasonic sensor value on the serial monitor.

Complete code:

1.3.5 Test Result

Open the serial monitor and set the baud rate.

Put an object in front of the ultrasonic sensor, and it will detect the corresponding distance value.

NOTE: The sensor is not professional and just used for learning.

1.4 Greeting Robot

Before learning: We combine the servos and ultrasonic sensor in this project. When the sensor detects any thing within the distance of 15~35CM, the greeting robot waves its arm as a welcome.

1.4.1 Test Code

1. In , make a variable to store the detected distance value.

2. Assign the detected distance value to the variable.

3. Set P0 and P1 servo to 0°.

4. In , put into “forever”.

And put and into in sequence.

When the ultrasonic sensor detects object(s) with the distance of 15~35CM;

P1 servo rotates within 0~90° to wave the arm.

Or else, the robot stops waving arm and put his arm to the original position.

Complete code:

1.4.2 Test Result

When someone approaches, the robot begins to greet him/her.

2. Troubleshooting

2.1 Code fails to download to Micro:bit

Problem

Recently, many users encounter the issue that Micro:bit board doesn’t respond when download code.

If the way you operate is correct, maybe you accidentally press the reset button and enter the Maintenance mode or the firmware is lost due to mis-operation.

Plug in Micro:bit board, the “MAINTENANCE” drive appears, which means the program can’t be downloaded.

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Solution

  1. Download the hex file from this page to your computer.

    Down load the latest micro:bit firmware-0255: https://www.microbit.org/get-started/user-guide/firmware/ If you do not want to download from this website, we also provide it in our tutorial.

  2. After the latest firmware is downloaded, then drag it into the “MAINTENANCE” to make Micro:bit back to normal mode.

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Avoid to Enter “MAINTENANCE”

  1. Make sure the Reset button is not pressed when plugging the board by USB cable.

img        2. Don’t unplug the cable suddenly during downloading micro:bit program, otherwise, the firmware will be lost and micro:bit will enter “MAINTENANCE” mode. 3. In the experiment, wrong wiring also cause a short circuit or firmware lost.

2.2 Troubleshooting-Download with WebUSB

Having trouble pairing the Micro: bit with WebUSB (/ device/usb/webusb)?

Step 1: Check cable

Make sure that your micro:bit is connected to your computer with a micro USB cable. You should see a MICROBIT drive appear in Windows Explorer when it’s connected.

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If you can see the MICROBIT, please go to step 2.

If you can’t:

  • Make sure that the USB cable is working. Does the cable works on another computer? If not, find a different cable to use. Some cables may only provide a power connection and don’t actually transfer data.

  • Try another USB port on your computer.

  • Is the cable good but you still can’t see the MICROBIT drive? Hmm, you might have a problem with your micro:bit.

  • Try the additional steps described in the fault finding at microbit.org.

  • If this doesn’t help, you can create a support ticket to notify the Micro:bit Foundation of the problem. If you do so, skip the rest of these steps.

Step 2: Check firmware version

It’s possible that the firmware version on the micro:bit needs an update. Let’s check:

  1. Go to the MICROBIT drive.

  2. Open the DETAILS.TXT file.

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  1. Look for the version number. It should say Version: …

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    Or Interface Version: …

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If the version is 0234, 0241, 0243, you need to update the firmware on your micro:bit. Go to Step 3 and follow the upgrade instructions.

If the version is 0249, 0250 or higher, you have the right firmware, just go to step 4.

Step 3: Update firmware

  1. Put your micro:bit into MAINTENANCE Mode.

    To do this, please unplug the USB cable from the micro:bit and then re-connect the USB cable after pressing and holding the reset button. Once you insert the cable, you can release the reset button. You should now see MAINTENANCE instead of the MICROBIT drive. Also, a yellow LED indicator will stay on.

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  1. Download firmware .hex file: https://microbit.org/guide/firmware/

  2. Drag the file into the MAINTENANCE drive.

  3. The yellow LED will flash while the HEX file is copying. After that, the LED will go off and the micro:bit resets. The MAINTENANCE drive now changes to MICROBIT.

  4. The upgrade is complete! You can open the DETAILS.TXT file to check the firmware version that matches the one of the HEX file you copied.

If you want to know more about connecting the board, MAINTENANCE Mode, and upgrading the firmware, please refer to Firmware guide.

Step 4: Check version of Browser

WebUSB may require you to update your browser.

Check that your browser version matches one of these: Android, Chrome OS, Linux, macOS and Windows 10 Chrome 65+.

Step 5: Pair device

Once you’ve updated the firmware, open the Chrome Browser, go to the editor and click on Pair Device in settings.

See WebUSB (/ device / usb / webusb) for pairing instructions.

3. Resources

Keyestudio official:

https://www.keyestudio.com/

Keyestudio wiki main page:

https://wiki.keyestudio.com/Main_Page

MicrobitCode:

https://makecode.microbit.org/

Microbit official:

https://www.microbit.org/