Tech Tinker Club — Microbit Pseudocode Specification (v2)

This document is the authoritative reference for Tech Tinker Club pseudocode used to describe MakeCode programs for the BBC micro:bit (and micro:bit v2).

It is designed for:

  • children aged 8–11 (KS2),
  • instructors and parents supporting them,
  • and for use in quizzes, worksheets, lesson notes, and teacher resources.

The aim is that every MakeCode block has a clear TTC pseudocode form.

1. Pseudocode Style

1.1 Keywords

All pseudocode keywords are written in UPPERCASE:

  • WHEN, IF, THEN, ELSE, END IF
  • REPEAT, END REPEAT
  • WHILE, END WHILE
  • FOR, END FOR
  • FOREVER, END FOREVER
  • EVERY, END EVERY
  • SET, TO, CHANGE
  • TRUE, FALSE
  • GAME OVER, etc.

Blocks that behave like events are written with WHEN … DO … END WHEN.

1.2 Variables

Variables are:

  • all lowercase,
  • words separated by underscores if needed.

Examples:

  • score
  • bird_y
  • light_level
  • best_time
  • obstacles
  • player_lives

Assignments use:

SET score TO 0
CHANGE score BY 1

1.3 System Values (Sensors, State, Random)

Values provided by the micro:bit itself (sensors, buttons, random, etc.) are written in square brackets:

[button A is pressed]
[light level]
[temperature]
[acceleration X]
[random number from 0 to 10]
[sound level]
[compass heading]
[runtime ms]

These are not variables you create; they are readings from the device or system.

They can be used inside conditions and expressions:

IF [light level] < 50 THEN
    show text "Too dark!"
END IF

SET guess TO [random number from 0 to 10]

1.4 Expressions

Anywhere you see <Expression> or <TextExpression> in this document, it means: “anything that behaves like a number (or text) in that place”, e.g.

  • score + 1
  • length of name
  • [light level] * 2
  • number from text input_text

1.5 Events

Event handlers have the general form:

WHEN [some event happens] DO
    ...
END WHEN

Examples:

WHEN [button A is pressed] DO
    CHANGE score BY 1
END WHEN

WHEN [shake gesture] DO
    GAME OVER
END WHEN

1.6 Indentation

Indentation is for readability only; it does not change meaning, but children are encouraged to indent code inside blocks:

IF score > 10 THEN
    show icon happy
ELSE
    show icon sad
END IF

2. Control Structures

These are the basic shapes we use in TTC pseudocode.

2.1 IF / ELSE

IF <condition> THEN
    ...
END IF

IF <condition> THEN
    ...
ELSE
    ...
END IF

2.2 Fixed Repetition

REPEAT <count> TIMES
    ...
END REPEAT

2.3 While Loop

WHILE <condition> DO
    ...
END WHILE

2.4 For Index Loop

FOR index FROM <start> TO <end> DO
    ...
END FOR

2.5 For Each Loop

FOR EACH element IN <list_name> DO
    ...
END FOR

2.6 Forever Loop

FOREVER
    ...
END FOREVER

2.7 Timed Loop

EVERY <time_ms> ms DO
    ...
END EVERY

2.8 Break / Continue (Advanced)

BREAK

CONTINUE

Used inside loops to exit early or skip to the next iteration.

3. System Values (Overview)

The micro:bit provides many built-in values. They are always written in square brackets.

Examples:

  • Buttons: [button A is pressed], [button B is pressed]
  • Gestures: [shake gesture]
  • Sensors: [light level], [temperature], [sound level]
  • Accelerometer: [acceleration X], [acceleration Y], [acceleration Z]
  • Compass: [compass heading], [magnetic force X], etc.
  • Rotation: [rotation pitch], [rotation roll], [rotation yaw]
  • Time: [runtime ms], [runtime micros], [time ms]
  • Game: SCORE, GAME IS OVER, GAME IS PAUSED
  • Radio: [received packet number], [received text], etc.
  • Music: [volume], [tempo bpm], [beat ms]

Each category below explains the relevant system values in more detail.

4. MakeCode to TTC Pseudocode Mapping

This chapter maps each toolbox category in the MakeCode editor to TTC pseudocode.

The section numbers follow the toolbox:

  • 4.1 Basic
  • 4.2 Inputs
  • 4.3 Music
  • 4.4 LED
  • 4.5 Radio
  • 4.6 Bluetooth
  • 4.7 Loops
  • 4.8 Logic
  • 4.9 Variables
  • 4.10 Maths
  • 4.11 Functions
  • 4.12 Arrays
  • 4.13 Text
  • 4.14 Game
  • 4.15 Images
  • 4.16 Pins
  • 4.17 Serial
  • 4.18 Control

Each block listed follows this pattern:

  • MakeCode block text
  • TTC pseudocode form(s)
  • Short explanation where useful

4.1 BASIC

This mirrors the Basic category in MakeCode.

4.1.1 Start and Forever

on start

ON START
    ...
END ON START

Runs once when the program begins.

You may also simply list commands at the top and say they belong in on start.

forever

FOREVER
    ...
END FOREVER

Main game loop; runs again and again.
(See also 4.7 Loops and timing notes in Appendix A.)

4.1.2 Display & Text

show number

show number <Expression>

show text (MakeCode: show string)

show text "<message>"
show text <TextExpression>

show icon

show icon heart
show icon happy
show icon sad
show icon skull

(Any built-in icon name.)

show leds

show leds
    0 0 0 0 0
    0 1 0 1 0
    0 0 1 0 0
    0 1 0 1 0
    0 0 0 0 0
end leds

show arrow

show icon arrow_north
show icon arrow_south
show icon arrow_east
show icon arrow_west
show icon arrow_northeast
show icon arrow_northwest
show icon arrow_southeast
show icon arrow_southwest

These are special cases of show icon.

clear screen

clear screen

4.1.3 Timing

pause (ms)

pause <Expression> ms

Used inside events, on start, or FOREVER.

4.2 INPUTS

Mirrors the Input category (including More… and micro:bit v2 blocks).

4.2.1 Events

WHEN [button A is pressed] DO
    ...
END WHEN

WHEN [button B is pressed] DO
    ...
END WHEN

WHEN [shake gesture] DO
    ...
END WHEN

WHEN [pin P0 is pressed] DO
    ...
END WHEN

WHEN [pin P0 is released] DO
    ...
END WHEN

WHEN [loud sound] DO
    ...
END WHEN

WHEN [logo is pressed] DO
    ...
END WHEN

4.2.2 Values

Buttons and logo:

[button A is pressed]
[button B is pressed]
[pin P0 is pressed]
[logo is pressed]

Movement and tilt:

[shake gesture]
[acceleration X]
[acceleration Y]
[acceleration Z]
[rotation pitch]
[rotation roll]
[rotation yaw]

Environment:

[light level]
[temperature]
[sound level]
[compass heading]
[magnetic force X]
[magnetic force Y]
[magnetic force Z]

Time:

[runtime ms]
[runtime micros]

Advanced configuration:

set accelerometer range to <g_value>
set loud sound threshold to <number>
calibrate compass

4.3 MUSIC

Mirrors the Music category, including micro:bit v2 sound.

4.3.1 Melody

play melody "<pattern>" once
play melody "<pattern>" until done
play melody "<pattern>" in background
stop melody

4.3.2 Tone and Rest

play tone C4 for 1 beat
play tone <frequency> Hz for <beats> beat
start tone C4
start tone <frequency> Hz
rest <beats> beat
stop all sounds

4.3.3 Volume and Tempo

set volume to <Expression>
[volume]

set tempo to <bpm>
change tempo by <bpm>
[tempo bpm]
[beat ms]

4.3.4 Sound Effects (micro:bit v2)

play sound giggle
play sound giggle until done
play sound <effect_name>
play sound <effect_name> until done
[sound is playing]

set built_in_speaker to on
set built_in_speaker to off

(Any sound expression can be treated as <effect_name>.)

4.4 LED

Mirrors the Led category (including More…).

4.4.1 Main LED Controls

plot <x> <y>
unplot <x> <y>
toggle <x> <y>
[pixel at <x> <y> is on]
plot bar graph <value> up to <max_value>

4.4.2 Brightness & Display

plot <x> <y> brightness <brightness_value>
[brightness of pixel <x> <y>]
[brightness]
set brightness <Expression>

set display enabled to on
set display enabled to off
stop animation

set display mode to black_and_white
set display mode to greyscale

4.5 RADIO

Mirrors the Radio category (including More…).

4.5.1 Group

set radio group to <number>

4.5.2 Send

radio send number <Expression>
radio send value "<name>" = <Expression>
radio send text "<message>"
radio send text <TextExpression>

4.5.3 Receive

Events:

WHEN [radio receives number] DO
    ...
END WHEN

WHEN [radio receives value] DO
    ...
END WHEN

WHEN [radio receives text] DO
    ...
END WHEN

Values:

[received packet number]
[received text]
[received value name]
[received value number]
[received signal strength]
[received serial number]

4.5.4 Advanced Radio

set radio transmit power to <level>
set radio transmit serial number on
set radio transmit serial number off
set radio frequency band to <band_number>
radio raise event from <source> with value <value>

4.6 BLUETOOTH

Mirrors the Bluetooth category (standard MakeCode; exact set may vary by version).

Pseudocode treats Bluetooth enable/disable and services in a general form:

bluetooth set enabled to TRUE
bluetooth set enabled to FALSE

bluetooth advertise <service_name>
bluetooth stop advertising

For classroom work, Bluetooth is usually either enabled once at startup or left off. Exact service blocks (e.g. UART, iBeacon) can be described in words for advanced groups.

4.7 LOOPS

Mirrors the Loops category.

REPEAT <count> TIMES
    ...
END REPEAT

WHILE <condition> DO
    ...
END WHILE

FOR index FROM <start> TO <end> DO
    ...
END FOR

FOR EACH element IN <list_name> DO
    ...
END FOR

EVERY <time_ms> ms DO
    ...
END EVERY

BREAK
CONTINUE

FOREVER is documented in 4.1 Basic.

4.8 LOGIC

Mirrors the Logic category.

4.8.1 IF / IF–ELSE

IF <condition> THEN
    ...
END IF

IF <condition> THEN
    ...
ELSE
    ...
END IF

4.8.2 Comparisons

<Expression> = <Expression>
<Expression> < <Expression>
<Expression> > <Expression>
<Expression> <= <Expression>
<Expression> >= <Expression>
<Expression> != <Expression>

4.8.3 Boolean Operators

<condition> AND <condition>
<condition> OR <condition>
NOT <condition>

4.8.4 Boolean Constants

TRUE
FALSE

4.9 VARIABLES

Mirrors the Variables category.

Creation is handled verbally (“make a variable called …”). In pseudocode we just use:

SET score TO 0
CHANGE score BY 1
SET bird_y TO 2
SET obstacles TO []

This corresponds to MakeCode’s:

  • set score to 0
  • change score by 1

We do not introduce extra syntax beyond SET and CHANGE.

4.10 MATHS

Mirrors the Math category.

4.10.1 Arithmetic

<Expression> + <Expression>
<Expression> - <Expression>
<Expression> * <Expression>
<Expression> / <Expression>

4.10.2 Remainder

remainder of <Expression> divided by <Expression>

4.10.3 Random

[random number from <a> to <b>]
[random true or false]

4.10.4 Min, Max, Constrain, Map

min of <Expression> and <Expression>
max of <Expression> and <Expression>

constrain <value> between <low> and <high>

map <value> from <low1>..<high1> to <low2>..<high2>

4.10.5 Absolute, Root, Rounding

absolute of <Expression>
square root of <Expression>
round <Expression>

(Optionally, for older learners: floor, ceiling, truncate.)

4.10.6 Constants and Advanced (Optional)

pi
e

<Expression> to the power of <Expression>
sine of <Expression>
cosine of <Expression>
tangent of <Expression>
arcsine of <Expression>
arccosine of <Expression>
arctangent of <Expression>

These are not all blocks in MakeCode, but may be useful in advanced contexts.

4.11 FUNCTIONS

Mirrors the Functions category.

4.11.1 Define a Function

MakeCode: function doSomething()

FUNCTION name (optional_parameters)
    ...
END FUNCTION

For KS2 we usually omit parameters:

FUNCTION reset_game
    SET score TO 0
    SET life TO 3
END FUNCTION

4.11.2 Call a Function

CALL reset_game

If you prefer, you can omit CALL and just write:

reset_game()

Both forms map to the same idea as the “call function” block.

4.12 ARRAYS

Mirrors the Arrays category.

4.12.1 Create

SET list TO [0, 1, 2]
SET text_list TO ["a", "b", "c"]
SET list TO []

4.12.2 Read

length of list
list[<index>]
get item at <index> from list
get and remove item at <index> from list
get and remove first item from list
get and remove last item from list
get random item from list

4.12.3 Modify

SET list[<index>] TO <Expression>
append <Expression> TO list
remove first item from list
remove last item from list
insert <Expression> AT BEGINNING OF list
insert <Expression> AT <index> IN list
remove item AT <index> FROM list

4.12.4 Operations

index of <value> in list
reverse list

Indexes start at 0.

4.13 TEXT

Mirrors the Text category.

4.13.1 Basic Text

""
"Hello"
"Crashy Bird"
length of <TextExpression>
join <TextExpression1> and <TextExpression2>

4.13.2 Conversions

number from text <TextExpression>
text from number <Expression>

4.13.3 Splitting, Searching, Substrings

split <text> at <separator>
<text> includes <search_text>
index of <search_text> in <text>
<text> is empty
substring of <text> from <start_index> length <length>
compare <text1> to <text2>
char from <text> at <index>
char code from <text> at <index>
text from char code <number>

4.14 GAME

Mirrors the Game category.

Sprites:

SET sprite TO CREATE SPRITE AT (x, y)
DELETE sprite
sprite IS DELETED
MOVE sprite BY <steps>
TURN sprite RIGHT BY <degrees>
TURN sprite LEFT BY <degrees>
CHANGE sprite X BY <value>
CHANGE sprite Y BY <value>
SET sprite X TO <value>
SET sprite Y TO <value>
X POSITION OF sprite
Y POSITION OF sprite
sprite IS TOUCHING other_sprite
sprite IS TOUCHING EDGE
IF sprite IS TOUCHING EDGE THEN
    BOUNCE sprite
END IF

Lives and score:

REMOVE LIFE <value>
ADD LIFE <value>
SET LIFE TO <value>

SET SCORE TO <value>
CHANGE SCORE BY <value>
SCORE

Countdown and game state:

START COUNTDOWN <milliseconds>
GAME OVER
GAME IS OVER
GAME IS PAUSED
GAME IS RUNNING
GAME PAUSE
GAME RESUME

4.15 IMAGES

Mirrors the Images category.

SHOW IMAGE <image> AT OFFSET <offset>
SCROLL IMAGE <image> WITH OFFSET <offset> INTERVAL <milliseconds>

SET my_image TO CREATE IMAGE:
    row1
    row2
    row3
    row4
    row5

SET my_big_image TO CREATE BIG IMAGE:
    row1
    row2
    row3
    row4
    row5

ICON <icon_name>
ARROW <direction>

4.16 PINS

Mirrors the Pins category (including More…).

Digital:

[digital reading from P0]
SET digital pin P0 TO <0_or_1>

Analog:

[analog reading from P0]
SET analog pin P0 TO <value_0_to_1023>
SET analog period of P0 TO <microseconds>
map <value> from <low1>..<high1> to <low2>..<high2>

Audio and servo:

SET audio pin TO P0
SET audio pin enabled TO TRUE/FALSE

SET servo on P0 TO angle <degrees>
SET servo pulse on P0 TO <microseconds>

More / pull / events / I2C / SPI:

SET pull of P0 TO up/down/none
SET P0 TO EMIT EDGE EVENTS
SET pitch pin TO P0

WHEN [pin P0 is pulsed high/low] DO
    ...
END WHEN
[pulse duration us]
pulse in us on P0 pulsed high/low

i2c read number at address <addr> format <format> repeated <TRUE_or_FALSE>
i2c write number <value> to address <addr> format <format> repeated <TRUE_or_FALSE>

SET spi frequency TO <value>
SET spi format TO <bits> bits MODE <mode>
spi write <value>
SET spi pins TO MOSI <pin> MISO <pin> SCK <pin>

4.17 SERIAL

Mirrors the Serial category.

Write:

serial write line <TextExpression>
serial write number <Expression>
serial write value <TextExpression> = <Expression>
serial write string <TextExpression>
serial write numbers <array_variable>

Read:

SET text TO serial read line
SET text TO serial read until <delimiter>
SET text TO serial read string

WHEN [serial data received <delimiter>] DO
    ...
END WHEN

Redirect and advanced:

serial redirect TX <pin_tx> RX <pin_rx> baud <baud_rate>
serial redirect to USB

serial set tx buffer size TO <size>
serial set rx buffer size TO <size>
serial write buffer <buffer_variable>
SET buffer_variable TO serial read buffer
serial set write line padding TO <value>
serial set baud rate TO <baud_rate>

4.18 CONTROL

Mirrors the Control category.

Events and background:

WAIT FOR EVENT FROM <source> WITH VALUE <value>

RUN IN BACKGROUND:
    ...
END BACKGROUND

Time and reset:

[time ms]
wait <microseconds> us
RESET DEVICE

Events:

RAISE EVENT FROM <source> WITH VALUE <value>

WHEN [event from <source> with value <value>] DO
    ...
END WHEN

[event timestamp]
[event value]

Appendix A — Advanced Notes for Instructors

This appendix contains guidance for adults using the spec with children.

A.1 Time and Loops

  • FOREVER + pause vs EVERY:
    • Use FOREVER + pause for simple game loops.
    • Use EVERY when you want a clean “tick” separate from other logic.
  • Avoid nested FOREVER blocks.

A.2 Randomness

  • Always explain that random blocks produce numbers, not text or sprites directly.
  • For arrays, emphasise:
    “Choose a random index, then use that index to read from the array.”

A.3 Arrays and Indexing

  • First element is always index 0.
  • Use number lines or box diagrams on the board to reinforce this.
  • Encourage children to trace through examples manually.

A.4 Events vs Polling

  • Highlight the difference between:
    • reacting to WHEN [button A is pressed] DO …
    • and checking [button A is pressed] inside FOREVER.
  • For radio, input and serial, prefer events when available.

A.5 Error Patterns to Watch For

  • Off-by-one errors in loops and random ranges.
  • Forgetting to update arrays when sprites are deleted.
  • Comparing only x or only y in collisions.
  • Mixing up assignment (SET score TO 0) with comparison (score = 0).

A.6 Suggested Progression

  • Start with:
    • Basic, Input, LED.
  • Then add:
    • Music, simple Loops, Variables.
  • Then:
    • Arrays, Text, Game, Radio.
  • Finally (optional for older KS2 / KS3):
    • Control, Serial, Pins, complex Maths.

End of Tech Tinker Club Microbit Pseudocode Specification (v2).