Linux Format - UK (2019-12)

50 LXF257 December 2019 http://www.linuxformat.com

TUTORIALS Node-Red

Twitter API key details. When done, click Add and the

node will update and show a connection. Now we need

to edit the node properties so that it searches “the

tweets of specific users” – in this case,my Twitter

account. For the name we call the node ‘Happy or not?’

and click Done.

Naughty or nice node?

This node will read all of my tweets and the data from

the tweet is going to be passed on to the next node

which is called ‘sentiment’, and is found in the ‘analysis’

section of nodes. Join the ‘Twitter’ node to the

‘sentiment’ node. The sentiment node checks the

content of our tweet against a word list, and if the

contents are deemed to be negative, a negative number

is outputted. If the content is neutral then 0 is

outputted. Positive content creates a positive number.

The next node is called ‘switch’ and is found in the

‘function’ nodes. Drag this node and connect the output

from sentiment to the input of the switch node. A

switch node works in the same manner as a conditional

statement: it routes the flow of our code based on logic.

In this case it will route the flow based on the sentiment

score. Double-click the switch node and edit as follows.

The name of the node is ‘Check the sentiment’ and

the Property is msg.sentiment.score. Then we need to

add three conditions to test. The first is if the score is

less than the number 0. So change this to < and make

sure that in the drop-down, the data format is set to

number , then add the number 0 in the text box. Now

click +add and in the next line we will check if the value

he Internet of Things (IoT) is a weird and

wonderful place, and in this tutorial we will

make it a little weirder by creating a tool that

reads the sentiment of our tweets and rates them

according to a list of positive and negative words. If the

tweet is positive, a green LED will light up; if it’s negative

a red LED will light. Neutral will see a yellow LED light.

This is a fun introduction to learning how we can

measure the mood of a tweet and create novel outputs.

We’ve kept components for this project simple. We

have three LEDs (red, yellow and green) connected to

pins GPIO17, 27 and 22 via their long leg, and connected

to GND via their short leg and a 330 ohm resistor.

Software setup

On the Raspberry Pi, we need to start the Node-RED

application, either via SSH or by attaching a keyboard

and mouse and screen. In a terminal type the following:

$ node-red-start

In the output look for the following message – the IP

address will be different.

Once Node-RED has started, point a browser at

http://192.168.0.4:1880

From another computer on the same network as the

Pi, go to this IP address and you will be greeted with the

Node-RED interface. Before we start any code we first

need to sign up for a Twitter Developer account at

https://developer.twitter.com and then go to

https://developer.twitter.com/en/apps to create

an app. Answer all of the required questions and the

app will be created. Then click ‘Keys and tokens’ and

make a note of the Consumer API keys (API key and

API secret key), and then under ‘Access token & access

token secret’, click Create and make a note of the

Access token and Access token secret. Do not share

these keys with anyone!

Back in Node-RED, there are a selection of nodes

(blocks of code/functions) that we can drag into a Flow

(the sequence of code). We can join these nodes

together by drawing lines from the grey circle on a node

• left-click the mouse button and drag to connect.
  The first node we shall use is from ‘social’ and it is
  the ‘Twitter’ input node (grey circle on right side.)
  Double-click the node and click the edit button next to
  ‘Add new twitter-credentials’, and then enter your

In Node-RED the code is made into a flow, where nodes are connected

to perform a task.

Monitor the mood

of Twitter tweets

Les Pounder

is a freelance

maker who works

with organisations

such as the

Raspberry Pi

Foundation to

promote maker

skills.

Any model of

Raspberry Pi

The latest

Raspbian

3x LEDs (red,

yellow, green)

3x 330 ohm

Resistors

Breadboard

3x female-

to-male

jumper wires

Computer

with net

connection

Code:

http://bit.ly/

lxf257twit

T

NODE-RED

OUR

EXPERT

YOU NEED

Les Pounder shows us how to use a Raspberry Pi and Node-RED to read

the sentiment of a tweet and control a colour-coded LED.

50 LXF257 December 2019 http://www.linuxformat.com

TUTORIALS Node-Red

TwitterAPIkeydetails.Whendone,clickAddandthe

nodewillupdateandshowa connection. Now we need

toeditthenodepropertiessothat it searches “the

tweetsofspecificusers”– inthiscase,my Twitter

account.Forthenamewecallthe node ‘Happy or not?’

and click Done.

Naughty or nice node?

This node will read all of my tweets and the data from

the tweet is going to be passed on to the next node

which is called ‘sentiment’, and is found in the ‘analysis’

section of nodes. Join the ‘Twitter’ node to the

‘sentiment’ node. The sentiment node checks the

content of our tweet against a word list, and if the

contents are deemed to be negative, a negative number

is outputted. If the content is neutral then 0 is

outputted. Positive content creates a positive number.

The next node is called ‘switch’ and is found in the

‘function’ nodes. Drag this node and connect the output

from sentiment to the input of the switch node. A

switch node works in the same manner as a conditional

statement: it routes the flow of our code based on logic.

In this case it will route the flow based on the sentiment

score. Double-click the switch node and edit as follows.

The name of the node is ‘Check the sentiment’ and

the Property is msg.sentiment.score. Then we need to

add three conditions to test. The first is if the score is

less than the number 0. So change this to < and make

sure that in the drop-down, the data format is set to

number , then add the number 0 in the text box. Now

click +add and in the next line we will check if the value

heInternetofThings(IoT)isa weirdand

wonderfulplace,andinthistutorialwewill

makeit a littleweirderbycreatinga toolthat

readsthesentimentofourtweetsandratesthem

accordingtoa listofpositiveandnegativewords.If the

tweetispositive,a greenLEDwilllightup;if it’snegative

a redLEDwilllight.Neutralwillseea yellowLEDlight.

Thisisa funintroductiontolearninghowwecan

measurethemoodofa tweetandcreatenoveloutputs.

We’vekeptcomponentsforthisprojectsimple.We

havethreeLEDs(red,yellowandgreen)connectedto

pinsGPIO17, 27 and 22 viatheirlongleg,andconnected

toGNDviatheirshortleganda 330ohmresistor.

Softwaresetup

OntheRaspberryPi,weneedtostarttheNode-RED

application,eitherviaSSHorbyattachinga keyboard

andmouseandscreen.Ina terminaltypethefollowing:

$ node-red-start

In the output look for the following message – the IP

address will be different.

Once Node-RED has started, point a browser at

http://192.168.0.4:1880

From another computer on the same network as the

Pi, go to this IP address and you will be greeted with the

Node-RED interface. Before we start any code we first

need to sign up for a Twitter Developer account at

https://developer.twitter.com and then go to

https://developer.twitter.com/en/apps to create

an app. Answer all of the required questions and the

app will be created. Then click ‘Keys and tokens’ and

make a note of the Consumer API keys (API key and

API secret key), and then under ‘Access token & access

token secret’, click Create and make a note of the

Access token and Access token secret. Do not share

these keys with anyone!

Back in Node-RED, there are a selection of nodes

(blocks of code/functions) that we can drag into a Flow

(the sequence of code). We can join these nodes

together by drawing lines from the grey circle on a node

• left-click the mouse button and drag to connect.
  The first node we shall use is from ‘social’ and it is
  the ‘Twitter’ input node (grey circle on right side.)
  Double-click the node and click the edit button next to
  ‘Add new twitter-credentials’, and then enter your

InNode-REDthecodeismadeintoa flow, where nodes are connected

toperforma task.

Monitor the mood

of Twitter tweets

LesPounder
isa freelance
makerwhoworks
withorganisations
suchasthe
RaspberryPi
Foundationto
promotemaker
skills.

Anymodelof

RaspberryPi

Thelatest

Raspbian

3xLEDs(red,

yellow,green)

3x 330 ohm

Resistors

Breadboard

3x female-

to-male

jumperwires

Computer

withnet

connection

Code:

http://bit.ly/

lxf257twit

T

NODE-RED

OUR

EXPERT

YOU NEED

Les Pounder shows us how to use a Raspberry Pi and Node-RED to read

the sentiment of a tweet and control a colour-coded LED.