BrickPi3 Getting Started – Program in Scratch

BrickPi3 Getting Started – Program in Scratch

Scratch Programming

180px-Scratchcat.svgScratch 1.4 comes pre-installed on all versions of Raspbian and allows you to control your BrickPi3 via a graphical user interface. However the Scratch interpreter which allows communication with the robot is only supported on Raspbian for Robots.

Scratch Principles

Interaction with the sensors and motors is done via the broadcast block and the sensor block. The Broadcast block sends a command to the BrickPi3 and the Sensor Value block reads the answer from the BrickPi3. They work hand in hand.

Anatomy of the broadcast block

Some broadcast examples:

MotorBroadcastExamplesBP3

Motor Broadcast

BroadcastExamplesBP3

Sensor Broadcasts

The broadcast block takes two parts:

  1. For a motor: it needs the motor address  (either the letter M or the word MOTOR followed by a letter from A to D) and the target
  2. For a sensor: it needs the sensor port address  (S1, S2, S3 or S4) and the sensor name.

Spaces are optional between each part and are there for readability only.  BrickPi3 offers a lot of flexibility in its Scratch programming so it can adapt to your style.

Controlling Motors

Motor targets are one of the following:

  1. to control the speed:  a number from 0 to 100, with or without the % sign
  2. to go at full speed: one of these words: ON, FULL
  3. to stop: one of these words: OFF, STOP
  4. to go a specific rotation: Position (or the letter P) followed by a number from 0 to 360
motors_full

Various ways of setting motor A to full power

motors_stop2

Various ways to stop motor A

Various ways to get half a rotation

Various ways to get half a rotation

If you’ve programmed with BrickPi+ before, you’ll notice there is no need to enable or disable motors.

Getting Motor Feedback

Reading the motor speed

Reading the motor speed

Reading Sensors

ExampleBrickPi3ScratchBlock

First you send a broadcast command to tell Scratch to go ahead and take a reading from the sensor. You will find the resulting reading in the sensor value block. Use the pulldown menu (the little down arrow) to select which value you are interested in as in the following image:

sensors_pulldown

Take note that you must send at least one broadcast before you can find the sensor in the sensor value pulldown menu as demonstrated in the following video:

If you have experience with BrickPi+ Scratch programming, you’ll notice that setting up sensors is no longer required.

Advanced Sensor Programming

Each sensor sends two extra values to Scratch for you to read: Status and Type.

Waiting for sensor readiness

Waiting for sensor readiness

The Status one will let you know if the sensor reading was successful or if there was an error. You can use this to determine if a sensor is ready to be read.
The Status can take four values:
SUCCESS, SPI_ERROR, SENSOR_ERROR and SENSOR_TYPE_ERROR

 

The Type sensor value will contain the type of the sensor. [[ I can’t come up with a scenario where it would be useful???]]

Reading multiple sensors

When you wish to get a reading from multiple sensors that have already been configured, you can do one of two things:
Use the Broadcast Update block, or use the Broadcast S1 block (also S2, S3 or S4) without the name of the sensor

Updating sensors and motors

Updating sensors and motors

updating sensors with a variable

updating sensors with a variable

Supported  Sensors

The following Sensors are supported in Scratch:

Sensor Type

Scratch Sensor name

Resulting Sensor Value

Short Explanation

LEGO EV3 Ultrasonic Sensor EV3US
EV3USCM
EV3USIN
EV3USLISTEN
US cm
US cm
US Inch
US Listen
default behavior (in cmd)
explicit use of cm
explicit use of inches
Listen mode
LEGO EV3 Gyro Sensor EV3GYRO
EV3GYROABS
EV3GYRODPS
EV3GYROABSDPS
Gyro ABS
Gyro ABS
Gyro DPS
Gyro ABS, Gyro DPS
same as EV3GYROABS
Absolute
Degrees Per Second
Both at the same time
LEGO EV3 Color Sensor EV3COLOR Color EV3 color sensor
LEGO EV3 Touch Sensor EV3TOUCH
TOUCH
Touch
Touch
use TOUCH if you use either an EV3 or a NXT sensor
LEGO EV3 Infrared Sensor EV3IR
EV3IRPROX
IR Prox
IR Prox
IR proximity sensor
LEGO NXT Ultrasonic Sensor NXTUS
ULTRASONIC
US cm
US cm
NXT Ultrasonic
LEGO NXT Color Sensor NXTCOLOR
COLOR
Color
Color
LEGO NXT Light Sensor
LEGO NXT Touch Sensor NXTTOUCH
TOUCH
Touch
Touch
 use TOUCH if you use either an EV3 or a NXT sensor
Analog Sensor (Sound Sensor, for example)
Dexter Industries dGPS
Dexter Industries dThermal  TEMP  Temp
Dexter Industries dPressure
Dexter Industries dTIR

 

Back to BrickPi3 Tutorials & Documentation

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