Nexus:bit User Manual v0.1 (English)

Nexus:bit
User Manual
Taiwan Coding
Education Association
v0.1

Taiwan Coding Education
Association
• Taipei headquarter
– Business hours:
• Mon/Tue/Thu/Fri 9:00-21:00
• Wed/Sat/Sun 9:00-18:00
– Address: 4F., No. 143, Sec. 1, Chongqing S. Rd.,
Zhongzheng Dist., Taipei City 100, Taiwan (R.O.C.)
– Tel: 00-886-2-2316-7734
– Email: service@beyond-coding.org.tw
– Official website: http://www.beyond-coding.org.tw
– Facebook: Taiwan Coding Education Association

Contents
1. Meet Nexus:bit (page 5)
2. Download MakeCode extension (page 20)
3. Nexus:bit basic features (page 28)
4. Nexus:bit advanced features (page 56)
5. PCA9685 servo control (page 84)

What is Nexus:bit？
• Nexus:bit is a powerful expansion board
designed for BBC micro:bit, a programmable
single-board microcontroller. micro:bits are
already full of wonderful features; with the
Nexus:bit it can be even better.
• You can use Nexus:bit for:
– Building robot/car or other motor devices
– Building Maker projects
– Make it as a mini game console

• Nexus:bit has the following built-in features:
– 18650 rechargeable lithium battery (2600 mAh,
included)
– Mini joystick board
– Buzzer (monotone speaker)
– RGB LED
– Vibration motor
– Microphone (sound level detection)
– Servo/DC motor pins
– And others

Nexus:bit features
Joystick/ultrasonic module slot
(P1, P2, P5, P11)
RGB LED
(PCA9685 13-15)
Mic (P12)
Buzzer (P0)
Buzzer switch
Vibrator (P8)
Mic sensitivity knob
I2C pins
micro:bit
full breakout pins
PCA9685
Servo pins
(1-12)
18650 lithium
battery
USB charging
port
Power/charging
Indicator LED
Power switch 5V/3.3V power
5V input
DC motor pins
(P13~16)
Single servo
pin (P12)
SPI pins

Nexus:bit vs. Thunder:bit
• What’s the difference between Nexus:bit and
TCEA’s earlier board Thunder:bit?
– Nexus:bit is the upgraded version of Thunder:bit, smaller,
has more servo pins and added microphone
– Thunder:bit has more room for connecting wires, the DC
motor ports are easier to use, with the possibility to
connect external A/B buttons
Left: Thunder:bit
Right: Nexus:bit

Safety
• Please use Nexus:bit in places far from
heat/water sources and keep your hands dry.
• Do not let water/metal contacts metal points
under the board or battery connections for
the risk of causing short circuit.

Lithium battery
• Install the battery as indicated in the next
page. Once installed, do not remove it without
absolute necessary.
• If you need to change battery, pry it out from
the negative end or middle with a flathead
screwdriver.
• Warning: DO NOT REVERSE BATTERY AND
TURN ON POWER

Battery direction
+
-
Power switch

• Turn off the Nexus:bit after using it.
• Recharge battery if you used it for quite some
time (see the following few pages).

Recharge battery
• Connect a micro USB cable to charging board, the
board would go into charging mode and stop
using battery power.
• It is recommended to recharge with 5V 1-2A
transformers. Using computer USB ports would
be slower.
• When charging the indicator LED would be red
(powered off) or yellow (powered on). The red
light would turn off once it’s fully recharged.
• After fully recharged, remove the USB cable.

Battery life
• How long can Nexus:bit’s 18650 lithium
battery (capacity 2600mAh) last?
– As in our test, when the board connected 8 SG90
servos and turn them simultaneously every half
second, it lasted almost 3.5 hours.

Power/charging indicator LED
Red light on means charging; after charging
it would turn off.

Power/charging indicator LED
If you turn on power while charging, it would be yellow
light (red + green)

Power/charging indicator
LED
Green light on when you simply turn on power

Install micro:bit
• It’s recommended to turn Nexus:bit off before
you install the micro:bit.
• Power on Nexus:bit before you flash code
onto micro:bit.
front

What is MakeCode editor？
• MakeCode is a graphic JavaScript block editor
developed by Microsoft, which is the most
common coding tool for micro:bit
• MakeCode editor: https://makecode.microbit.org/
• MakeCode also allows users to define custom
blocks. We will introduce TCEA’s Nexus:bit
extension, which integrate various control
functions for Nexus:bit.

Download extension
• Open MakeCode editor, go to Advanced ->
Extension…and enter nexusbit, nexusbot or
TCEA in the search box. Click the extension to
import it.

Change the language if you
need to

Enter nexusbit and import
It might take a while depending on Internet status.
You can also copy/paste the this link to search:
https://github.com/alankrantas/pxt-Nexusbit

• Pins are signal input/output channels of
microcontrollers, like a electronic switch.
• Most of Nexus:bit’s features are connected to
specific pins of micro:bit, so they can actually
be controlled by original MakeCode blocks.
However our extension significantly simplified
the process.

Buzzer (pin 0)
• This block plays specific sound via buzzer
(frequency = 0 is no sound). Set duration as 0
means forever.

Buzzer (pin 0)
• You can also use original music blocks in
MakeCode:

Buzzer (pin 0)
• If you wish to read analog signal of pin 0
without triggering buzzer, you can remove the
jumper hat behind buzzer.
• Put away the jumper hat properly!
jumper hats

Buzzer switch
Remove the jumper hat will “cut off” buzzer

Joystick (pin 1, 2, A/B button)
• The slot in front of Nexus:bit can be used to
install the mini joystick board:

Install joystick board
Make sure it’s properly installed

Joystick direction
X axis (left/right) = pin 1 Y axis (forward/backward) = pin 2
A/B button function is the same as micro:bit’s own A/B button (pin 5, pin 11)
前
後
左右
rightleft
for-
ward
back-
ward

Joystick safety notice
• It is recommended to put your index fingers
under the side of joystick board as support.
Try not to press the joystick board down too
hard.
• Do not touch the metal dots under the
joystick board – this may cause signal anomy
from the joystick.
• If your code uses the joystick board, install it
properly before powering up Nexus:bit.

Joystick (pin 1, 2, A/B button)
• Determine if the joystick is pushed to a certain
direction (forward/backward/left/right/center,
which return true/false)：

Joystick sensitivity
• You can adjust the sensitivity of joystick: (with
high sensitivity, the joystick only needs to be
pushed a bit to determined directions.)

Read joystick analog signals
• The two 2 axis of the joystick in fact would
return analog signals to indicate their position.
We can read the analog values as well:

Vibration motor (pin 8)
• The vibration level can be set between 0-1023
(1023 = full power). Duration set as 0 means
forever.
– Note: since the vibrator is rather powerful, it is not
recommended to use it at full power.

• This pin can be used to connect 1 servo and
allow user control it with this block:
Single servo pin (pin 12)

S signal
+ power
- ground

• You can still use the original servo block in
MakeCode editor. If you want a quick servo
test without importing the Nexus:bit
extension, this would be very useful.

Microphone (pin 12)
• The mic on Nexus:bit detects sound volume
differences, not the quality of sound itself.
• The block would return True if the sound is
loud enough; otherwise return False.

Adjust mic sensitivity
Rotate the knob by flathead screwdriver to change
the sensitivity of mic. (Clockwise = more sensitive)

Pin 12 signal indicator LED
The LED would light up whenever the mic heard sound
(you can use it to judge the sensitivity) or pin 12 servo has received signal.

Note on mic/servo usage mix
• Since mic and single servo pin share pin 12,
using both would cause dysfunction for the
mic and servo. (For example, the servo may
jittering when the mic heard sound.)
• Please not mix the both in the same program,
or using PCA9685 servo blocks in this manual’s
section 5.

RGB LED
• The RGB LED on Nexus:bit is in fact connected
to onboard PCA9685 chip; the blocks in the
extension will take care of necessary settings
so it’s pretty easy to control.
• When powering up Nexus:bit, RGN LED would
light up as white (default) unless you set it to
other colors.

RGB LED
• We can select 8 pre-set colors for RGB LED
with brightness control (0-100, 100 =
brightest):

• We can also set a specific color or randomized
color:

Select board type
• This extension is applicable to Thunder:bit
V2/V1 expansion boards. (Default is set to
Nexus:bit if you don’t select boards.)

Select board type
• Since Thunder:bit has less PCA9685 servo pins
and different RGB LED pins, it is necessary to
use the “Select board type” block on them.
• The mic block would not work when you
selected Thunder:bits (always return False).

Plug-in ultrasonic module
• The joystick slot on Nexus:bit can be used to
plug in a HC-SR04/HC-SR04P ultrasonic
module. The module is useful for robots and
cars to detect objects and avoid obstacles.
• HC-SR04 is one of the most common
ultrasonic modules on the market with
reliable detection distance within 1-2 meters.

HC-SR04 ultrasonic modules
HC-SR04 (original) ->
Power: 5V
<- HC-SR04P (newer version)
Power: 3.3-5V

HC-SR04 vs HC-SR04P?
• The two models has the same functionality
and pins. The differences are appearance, pin
installation direction and input voltage. Both
works with Nexus:bit and Thunder:bit.
• The NexusBot robot has to use HC-SC04P (see
the NexusBot assembly manual).

HC-SR04P module
Vcc (power, 3.3-5V)
Trig (trigger)
Echo (echo)
Gnd (ground)

Install HC-SR04P
Vcc->5V
Trig->P5
Echo->P11
Gnd->G
The 4 slots in the middle
front

Detect distance of objects
• Read the detected distance (cm) from the
ultrasonic module:
* The reading may be slight different than the actual distance; however
It still reflects the relative distance of objects.
Also, if the object is moving, the reading may varies or occasionally return 0.

Detect distance of objects
• We can also directly determined if objects are
closer or farther than certain distance:
※This block would ignore value 0 readings

Note on using ultrasonic
modules
• When you use the joystick slot to use an HC-
SR04/HC-SR04P module, it will use pin 5 and
pin 11, which are pins originally reserved for
micro:bit’s button A and B. Hence, the A and B
button blocks would not function normally
when you are using the ultrasonic module.

DC motors (pin 13/14, 15/16)
• Pin 13-16 are connected to two sets of DC
motor pins, which allows motors to rotate in
either direction at full or slower speed.
• The DC motor pins on Nexus:bit are designed
for the NexusBot car, which uses special DC
motors, so the A1/A2 and B1/B2 marks are in
opposite direction.

DC motors (pin 13/14, 15/16)
(pin 15) B2 A1 (pin 13)
(pin 16) B1 A2 (pin 14)

DC motor in servo body
This is the type used by the NexusBot car.
For details, see TCEA’s NexusBot assembly manual.

Normal DC motors
• To use normal DC motors, you’ll need to add
jumper wire connectors.

Control DC motors
• The rotate direction and speed (-100 to 100)
in controllable:
The absolute value
represent speed,
+ and - means
direction.

2WD DC motor car
• The extension has implemented a block to
directly control 2WD DC motor cars – go
forward/backward, turn left/right or stop.
– NexusBot car is controlled a bit differently; check out the
NexusBot manual for details.

DC motor car example
• The regular DC motor version
See TCEA’s remote car assembly manual for details (no translation yet).
Basically, the motor connections nearer ground will be connect
to P13 and P15.

Stepper motors
• This block can be used to drive a 5V stepper
motor:
Every time you use this block the stepper motor
would go 1 “step”.
For example, a 28BYJ-48-5V motor needs to go
512 steps to turn a full circle.
Since the “forever” loop has a tiny delay, you can
use while loop to speed up the turning speed.

Stepper motors
This manual does not include tutorial about 28BYJ-48-5V
stepper motors and ULN2003 driver boards.

2WD stepper car
• The extension also
allows user to
control a 2WD
stepper motor car.
– If you are using pins
shared by micro:bit’s
LEDs, it is recommended
to disable LED screen.

I2C/SPI pins
• I2C (Inter-Integrated Circuit) and SPI (Serial
Peripheral Interface) pins allow us to connect
various electronic modules, for example,
devices originally designed for Arduino and
Raspberry Pi.
• This enables us to create more advanced
Maker projects.

I2C device connect example
Example of using a “0.96 OLED screen module.
Look up I2C devices’ wiring and usage before connecting them.

SPI pins
SPI預設腳位：
P13 = SCK, P14 = MISO, P15 = MOSI, P16 = CE

SPI device connect example
Example of using 4 linked MAX7219 matrix LED modules.
Look up SPI devices’ wiring and usage before connecting them.

Reassign SPI pins
• Since DC motor pins are also connected to
P13-16, if you wish to use SPI devices at the
same time, please reassign the SPI pins:

What is PCA9685？
• PCA9685 is a chip which allows multiple
servos’ control. Nexus:bit (and Thunder:bit)
has this built-in.
• Thanks to PCA9685, micro:bit now can control
motor devices such as MeArm (4 servos) or
biped robots with hands (8 servos or more).
• Nexus:bit can control as many as 12 servos via
PCA9685.

PCA9685 servo pins
S signal
+ power
- ground
S1 = servo 1, S2 = servo 2, all the way to
S12 = servo 12。

Nexus:bit’s servo package
• The Nexus:bit extension has implemented a
powerful servo control package:
– It would record servo positions and prevent them
turning to degrees outside 0-180 (so servos won’t
be jammed and overheat)
– Servos can be controlled by direct or relative
mode
– Multiple servos can be assign degrees at the same
time
– Servos can turn gratually

Direct degree setting
• It’s similar to the MakeCode servo block; you
can turn servos to 0-180 or min/max degrees.
• Servo no 1-12 (Nexus:bit) or 1-4 (Thunder:bit)
* If the board is selected as Thunder:bit, setting degrees for
servo 5-12 won’t take any effects.

Relative degree setting
• We can also assign relative turning degrees
(from default position) to servos.
– All servos’ default position are 90 degrees, so turn -90
means 90 – 90 = 0 degree, +90 means 90 + 90 = 180
degrees.

The advantage of relative mode
• Users don’t need to assign actual degrees, just
relative movements.
• You just need to calibrate the default position
and leave rest of the parameters untouched.
• It is recommended to use “All PCA9685 servos
turn to default” in “on start” to make sure
servos reset properly and synchronize with the
code.

Configure default/min/max
degrees
• The default/min/max degrees of every servo
can be configured:
The default position has to be set between
min and max degrees.
If max is smaller than min, it would be set
as the same value as min.
If default position is outside min and max,
it would be set to either min or max.

Configure example
• Set servo 1’s default as 80, min as 30 and max
as 150. Now we turn it to relative -60 and 60
degrees repeatedly.
– 80 – 60 = 20, however 20 degrees is lower than min (30),
so the servo is only allowed to be turned to 30.
– 80 + 60 = 140, within max (150), so it would be turned to
140.
• All PCA9685 servos in the extension will obey
the configured parameters in all conditions.

Gradually turning
• “Gradually turning” is to turn servos a bit at a
time, creating smooth turning effects and
allow motor devices to have finer
performance.
• The gradually turning blocks would only turn
servos a bit every time, so you’ll have to use
loops to for continuous turning.

Gradually turning example 1
• Turn the servo gradually toward either end by
pressing button A or B. The extension would
stop the servo turning once it reached min or
max degrees.

Gradually turning example 2
• Add position check with while loops (which
can be interrupted when needed:)

• The occasions to use position check blocks:
– If you wish the code stop setting degrees once the
servo has reached target;
– If you wish to do something else once the servo
has reached target;
– If you wish to add other logic blocks to stop servo
turning early when needed.

Gradually turning degree
• In the servo configure block, gradually turning
degree means the turning speed (degrees
changed every time).

• If servo 1 turned to default 90 degrees, with
gradually turning degrees = 5 and gradually turn
to 120, the degrees would be 95, 100, 105, 100,
115 then 120 respectively (turning 6 times).
• The gradually turning degrees and delay time
between turning would determine the speed and
smoothness of turning.
• Servos will always turn to exact target degrees
and stop.

Turn multiple servos at the
same time
• The extension also has blocks for multiple
servo control, including direct and relative
mode.
• We will only talk about the relative mode,
which is the most convenient way to control
motor devices like robots.

Turn multiple servos at the
same time
• We can input a number array to turn multiple
servos at the same time. The example is to
gradually turn 4 servos until all 4 of them
reached targets.
1 2 3 4 Servo no.
You can drag a array setting
block and borrow the array.
Servos that not set (in this
example servo no. 5-12) would
be ignored.

Set multiple servos at the
same time
Set gradually turning
Degrees for 8 servos.
If the array is longer
than max servos (
Nexus:bit = 12,
Thunder:bit = 4)
the block would not
function.

Design continuous movement
This is a continuous movement
for 4 servos (no. 1-4), move 2
at a time.
This is actually how biped robots
walk.

• If you wish to let certain servos maintain
position while setting multiple servos’ degrees,
put “null” block in the corresponding array
slot. Servos with new degrees set as “null” will
be ignored.

Design continuous movement 2
This example is the same as before,
other than allowing user to break loops
when needed,

Note on gradually turning
servos
• Since the extension need to calculate each
servos’ positions, if you gradually turn more
than 4-5 servos at the same time, overall
turning speed would drop, even causing
servos jittering.

THE END
Thank you so much for purchasing and using our product!

Nexus:bit User Manual v0.1 (English)

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Nexus:bit User Manual v0.1 (English)