Pi Sailboat

My daughters and I have built a number of boat projects with an assortment of Arduino, ESP-8266, Bluetooth and RFI components. I believe that this version using a Raspberry Pi and NodeRed offers one of the simplest solutions. This sailboat used a basic catamaran design with a Raspberry Pi mounting inside a waterproof container. Using NodeRed dashboards you can control the sailboat’s rudder from a smart phone. The complete NodeRed logic consisted of only 6 nodes.

Building the Sailboat

There are a lot of different building materials that you could choose from. K’Nex construction pieces are lighter than either Lego or Meccano and they allow you to create reasonably large structures with a minimal number of pieces. If you do not have access to K’Nex pieces then popsicle sticks and some card board would offer a good low cost solution.

To build the sailboat we used:
• K’Nex building pieces
• 4 plastic bottles
• 1 small plastic container with a lid
• String
• Duct tape
• Garbage bag
• Low torque servo
• Raspberry Pi Zero W or Pi 3
• Small USB phone charger

The base of the sailboat was a rectangular structure with 16 down facing K’Nex pieces that allowed plastic bottles to be duct taped in place.

boat_bottom

A few K’Nex pieces were used to create a compartment for the servo, and wire was used to secure the servo in place. A rudder was built by screwing a small piece of wood into the servo arm.

servobox

A garbage bag was cut to the required size and taped to the mast. The boom had a swivel connection to the mast and guide ropes were connected to both the boom and mast.

sailboat_details

Servo and Rudder Setup

Only very low torque servos can connected directly to Rasberry Pi GPIO pins.

Pi_servo_wiring

An example of a low torque servo would be the TowerPro SG90 ($4) that has a torque of 25.00 oz-in (1.80 kg-cm). If you have larger torque servos you will need to either use a custom Raspberry Pi servo hat (there are some good ones on the market), or you will need to use a separate power and ground circuit for the servo.

The wiringPi tool gpio can be used to control the servo. This package is pre-install in the Raspbian image, or it can be manually installed by:

sudo apt-get install -y wiringpi

Servos typically want a pulse frequency of 50 Hz, and the Raspberry Pi PWM (Pulse Width Modulation) pins have a frequency of 19200 Hz, so some range definitions and scaling is required:

gpio -g mode 18 pwm #define pin 18 as the PWM pin
gpio pwm-ms #use 'mark space' mode 
gpio pwmc 192 # set freq as 19200
gpio pwmr 2000 # use a range of 2000

The gpio pwm commands are not persistent after a reboot. A simple solution for this is to put these commands in the Pi user login file of: $HOME/.bash_login.

After the pwm setup commands are run you need to do some manual testing to define your different rudder (servo) positions (Figure 6), such as “Hard Left”, “Hard Right”, “Easy Left”, “Easy Right” and “Straight”. The pwr timing numbers will vary based on your requirements and servo arm positioning, for our sailboat we used:

gpio -g pwm 18 200 #straight
gpio -g pwm 18 260 #hard left
gpio -g pwm 18 140 #hard right
gpio -g pwm 18 230 #easy left
gpio -g pwm 18 170 #easy right

servo_settings

NodeRed Logic and Dashboards

NodeRed is pre-installed on the Raspbian image, but it will need to be set to autostart on a Pi reboot:  sudo systemctl enable nodered.service

NodeRed has a web configuration interface that is accessed by: http://localhost:1880 or http://pi_ip_address:1880.

On the options button (far right), by selecting: View -> Dashboard , you can define and change the web dashboard layouts.

dashboard

To create logic, nodes are selected from the left node panel and dragged and dropped on to the center flow panel. Logic flow are then created by clicking and joining together different inputs and outputs on the nodes. If a dashboard node is dropped on the flow panel it will be added to the default web dashboard. The gpio -g pwm commands can be called using the exec node. The button dashboard node will pass the defined payload value, for example a “Hard Left” 260 is passed when the button is pushed. The button’s payload value will be appended to the exec command to make a complete gpio -g pwm servo position command.

nodered

Once you’ve completed your logic setup press the Deploy button on the top right to make your configuration live and ready to test.

The final step is to enable a smart phone or tablet to connect to the Raspberry Pi, this can be done by either making the Raspberry Pi a WiFi access point or by tethering the Pi to a cell phone. There are some great guides on how to setup a Raspberry Pi as an access point. For this project the simple tethering method was used. Once the Pi is tethered to a phone, the PI’s IP address can be obtained from the hotspot users list.

pi_address

The NodeRed dashboard is accessed on your phone by: http://pi_ip_address:1880/ui .

nodered_ui

Assuming that everything is connected correctly you should be able to control the sailboard with your phone.

Summary

Once you’ve mastered the basic NodeRed and sailboat construction other projects such as motor boats, iceboats, airboats are possible.

airboat

 

 

 

Arduino talking MQTT to Node-Red

There are some great Arduino modules with integrated ESP-8266 wireless chips, some of the more popular modules are:

  • Adafruit HUZZAH
  • NodeMCU
  • WeMos

These modules allow you to do some interesting IoT (Internet of Things) projects. To connect the Arduino modules to PCs, Raspberry Pi’s or Linux nodes that are a number of communication choices. MQTT (Message Queue Telemetry Transport) is becoming one of the standards for this and it is pre-installed with Node-Red.

Plant Moisture Monitoring MQTT Example

Ard_mqtt_overview2

For our example we wanted to do a simple plant moisture example that used a solar charger and an Arduino Wemos module. We then setup an MQTT server on our Node-Red Raspberry Pi with a web dashboard.

Our goal was to get the MQTT technologies working, with some moisture inputs (and not a final plant monitoring system).

Moisture Sensors

Moisture sensors are very low cost and they start at about $2. The basic moisture sensor has 3 inputs; VCC, GND, and AO. Some sensors also include a digital output with a potentiometer to adjust the digital 0-1 moisture limit.

Our Arduino plant moisture setup is good for testing but not a good long term solution. When voltage is applied long term to moisture sensors ionization in the soil will cause a combination of false reading and deterioration of the sensor plates. We plan to do a future project where we will use relays to turn the sensors on/off and we will include solenoid values in a watering system.

MQTT on Arduino

There are a number of excellent MQTT libraries for Arduino, for this example we used the PubSubClient library. This library can be installed from the Arduino IDE by selecting the menu items:

Sketch -> Add Library -> Manage Libraries

To get MQTT setup you’ll need to:

  • define the SSID and password for your WAN
  • define the IP address for the MQTT server (the Node Red/Raspberry Pi node)
  • define some topic for the data

The nice thing about MQTT is that you can define topics for each of your data points. For this example we define the topic humidity to show the moisture sensor value, and msgtext to show the message (‘Needs Water’ or ‘).

Below is our sample Arduino code for passing the moisture data to our MQTT server.

/*
 Basic ESP8266 MQTT publish client example for a moisture sensor
*/
#include <ESP8266WiFi.h>
#include <PubSubClient.h>

// Update these with values suitable for your network.
const char* ssid = "YOUR_SSID_NAME";
const char* password = "YOUR_PASSWORD";
const char* mqtt_server = "YOUR_NODE_RED_IP";

WiFiClient espClient;
PubSubClient client(espClient);

void setup_wifi() {
  // Connecting to a WiFi network
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void reconnect() {
  // Loop until we're reconnected
  Serial.println("In reconnect...");
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect("Arduino_Moisture")) {
      Serial.println("connected");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      delay(5000);
    }
  }
}

void setup() {
  Serial.begin(9600);
  setup_wifi();
  client.setServer(mqtt_server, 1883);
}

void loop() {
  char msg[10];
  char msgtext[25];
  String themsg;
  if (!client.connected()) {
    reconnect();
  }
  
  int soil_moisture=analogRead(A0);  // read from analog pin A0
  Serial.print("analog value: ");
  Serial.println(soil_moisture);
  
  if((soil_moisture>300)&&(soil_moisture<700)) {
    Serial.println("Humid soil");
    sprintf(msgtext,"Humid soil",soil_moisture);
  } 
  else if ((soil_moisture>700)&&(soil_moisture<950)){
    Serial.println("Moist Soil");
    sprintf(msgtext,"Moist Soil",soil_moisture);
  }
  else if (soil_moisture <300) ){
    Serial.println("Needs water");    
    sprintf(msgtext,"Needs water",soil_moisture);
  }
  else
  {
      sprintf(msgtext,"Sensor Problem",soil_moisture);
  }

  sprintf(msg,"%i",soil_moisture);
  client.publish("humidity", msg);
  client.publish("soil", msgtext);
  delay(5000);
}

Node-Red

Node-Red is an excellent visual programming environment that is part of the Raspberry Pi base install. Node-Red is a simple tool to create your own Internet of Things applications. The base Node-Red installation includes MQTT interfacing components but it does not include an MQTT server.

If you don’t have a Raspberry Pi you can install Node-Red on Window, Mac OS or Linux systems. I’ve had good results running Node-Red on a very old low end laptop running Xubuntu, (see steps 1-3 in this linked guide).

MQTT Server on Node-Red

There are a number of free internet MQTT servers (iot.eclipse.org) that can be used or an MQTT server can be loaded directly on a local server (i.e. Mosquito).

Mosca is a standalone MQTT server that can be installed directly into Node-Red. The Mosca Node-Red component can be either installed at the command line by:

cd $HOME/.node-red

npm install node-red-contrib-mqtt-broker

Or the component can be install within the Node-Red web interface by selecting the “manage palette” option, and then search for mosca.

mosca_install

After Mosca is installed, all that is required is that a “mosca” node needs to be dragged and dropped into the Node-Red project.

mosca_mqtt_nodes

To connect the Arduino module to Node-Red mqtt inputs are added to the project.  The Arduino topics are defined in Node-Red by double-clicking on the mqtt node and then define the topic to match the Arduino topic.

mqtt_topic

After the MQTT connections are configured Web dashboards can present the final data. The Web dashboards offer a number of different components that could be used for this example I used a gauge and a text node.

To compile and view the Node-Red application, click on the Deploy button on the right side of the menu bar. To access the web dashboard enter: http://your-ip:1880/ui . Below is a example of what you should see.

NodeRed_MQTT_GUI

Final Thoughts

The Mosca MQTT server component allows for a simple standalone architecture to connect wireless Arduino modules into a Node-Red IoT solution.

We can also load Node-Red on Raspberry Pi data collection nodes, and have them publish data to a central Node-Red server.

 

 

 

Arduino talking TCP to Node-Red and Python

There are some great Arduino modules with integrated ESP-8266 wireless chips, some of the most popular of these modules are:

  • Adafruit HUZZAH
  • NodeMCU
  • WeMos

Along with these modules comes some excellent libraries.

For Arduino to PC or Raspberry Pi communications that are a few options to choose from. A TCP client/server is simple and straightforward and it is excellent for sending single point information. For sending multiple data points take a look at MQTT (Message Queuing Telemetry Transport), it’s a common standard for IoT applications and it’s built into Node-Red.

Arduino TCP Client

The Arduino module can be a simple TCP client that can talk to either a Python or a Node-Red TCP server. Below is an example that sends a random integer to a TCP server every 5 seconds.

/*
Test TCP client to send a random number
 */
#include <ESP8266WiFi.h>
#include <ESP8266WiFiMulti.h>

ESP8266WiFiMulti WiFiMulti;

void setup() {
    Serial.begin(9600);

    // We start by connecting to a WiFi network
    const char * ssid = "your_ssid";       // your WLAN ssid
    const char * password = "your_password"; // your WLAN password
    WiFiMulti.addAP(ssid, password);

    Serial.println();
    Serial.print("Wait for WiFi... ");

    while(WiFiMulti.run() != WL_CONNECTED) {
        Serial.print(".");
        delay(500);
    }
    Serial.println("WiFi connected");
    Serial.println("IP address: ");
    Serial.println(WiFi.localIP());
    delay(500);
}

void loop() {
    const uint16_t port = 8888;          // port to use
    const char * host = "192.168.0.123"; // address of server
    String msg;

    // Use WiFiClient class to create TCP connections
    WiFiClient client;

    if (!client.connect(host, port)) {
        Serial.println("connection failed");
        Serial.println("wait 5 sec...");
        delay(5000);
        return;
    }
   
    // Send a random number to the TCP server
    msg = String(random(0,100));
    client.print(msg);
    Serial.print("Sent : ");
    Serial.println(msg);
    client.stop();    
    delay(5000);
}

Node-Red TCP Server

Node-Red is an excellent visual programming environment that is part of the Raspberry Pi base install. Node-Red is a simple tool to create your own Internet of Things applications. The base Node-Red installation includes a TCP server and client.

To install the web dashboards enter:

sudo apt-get install npm
cd ~/.node-red
npm i node-red-dashboard

To start Node-Red either use the on-screen menus or from the command line enter:

node-red-start &

Once Node-Red is running the programming is done via the web interface at: //localhost:1880 or //your_Pi_ip_address:1880 .

To configure the TCP server, go to the Input nodes section and drag and drop the TCP in node. After the node is inserted double-click on it and edit the port and message settings.

nodered_tcp

To create a gauge Web dashboard, go to the dashboard nodes section and drag and drop the gauge node. After the node is inserted double-click on it and edit the dashboard group, labels and ranges.

nodered_tcp_gauge

For debugging and testing an output debug node is useful.

To access the Web dashboard enter: //localhost:1880/ui or //your_Pi_ip_address:1880/ui

TCP Python Server

The python TCP server will see the incoming Arduino message as a Unicode (UTF-8) text, so convert message to an integer use: thevalue = int(data.decode(“utf-8”)). Below is the full code.

import socket
import sys

HOST = '' # Symbolic name, meaning all available interfaces
PORT = 8888 # Arbitrary non-privileged port

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print ('Socket created')

#Bind socket to local host and port
try:
s.bind((HOST, PORT))
except socket.error as msg:
print ('Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1])
sys.exit()

print ('Socket bind complete')

#Start listening on socket
s.listen(10)
print ('Socket now listening')

#now keep talking with the client
while True:
#wait to accept a connection - blocking call
conn, addr = s.accept()
data = conn.recv(1024)
print ('Connected with ' + addr[0] + ':' + str(addr[1]) + " " )
thevalue = int(data.decode("utf-8"))
print ("Value: ", thevalue)

s.close(

Summary

In our final application we mounted the Arduino module outside and we powered it with a small solar charger. We also include a humidity value with the temperature, and we used a QR code that linked to our web page.

Wake Up !!! Wake Up !!!

The goal of the “Wake me up” programs is to set a wake time that will turn on the lights and say something like: “Wake Up Wake Up”.  The logic was done in Node-Red and it was quite straightforward. The hardware used was:

The PowerSwitch Tail II ($26) is a power cord that is enabled/disabled with I/O pins. The PowerSwitch pins connect to GPIO18 and GND on the Pi. A desk light is plugged into the PowerSwitch Tail and speakers are connected to audio jack on the Pi.

pi2switch

With the PowerSwitch Tail II there are a lot of devices that could be controlled. For us, we simply connected it to a desk lamp. The setup shown below was later moved into a bedroom and place on a bedside table.

wakeup_hwd

For this project two Node-Red libraries were used; a scheduler library and a text to speech library. They are installed by:

 sudo apt-get install festival
cd $HOME/.node-red
npm install node-red-contrib-say
npm install node-red-contrib-simple-weekly-scheduler 

After the packages are loaded restart the Pi, and then start up Node-Red. On the Node-Red configuration Web page, drop a scheduler, and wire a Pi GPIO, and a Say node to the scheduler.

3nodes

Double-click the scheduler node and set the wake up times. The start/end payloads are numeric and 1/0. Below is the scheduler configuration.

schedule

For the Pi GPIO node, set the GPIO to Pin 12/GPIO18.

powerinfo

Next for the Say node, enter the text you want spoken .

wakeup

For the final circuit, inject nodes can be included for testing. An “on” inject sends a 1, and an “off” inject sends 0. At the wake up time the schedule node will send a payload that will trigger the speaking of the wake up text and the desk light will be turned on for 15 minutes.

final_wakeup

Pi/Node-Red Car

The goal of the Pi/Node-Red car project was to create a small vehicle that can be controlled from a smart phone . For the project we used:

  • 1 Car chassis for Arduino ($15)
  • 1 Pimoroni Explorer HAT Pro  ($23)
  • 1 Portable microUSB charger
  • 1 USB WiFi Adapter
  • 4 short alligator clips and 4 connectors
  • Duct tape

The Arduino car chassis may require a small amount of assembly. Rather than soldering connections we like to use short alligator clips. It is not recommended to wire DC motors directly to a Raspberry Pi so the Pimoroni Explorer HAT Pro is used to connect the 2 DC motors.

The Raspberry Pi and the portable microUSB charger are secured to the top of the car chassis with duct tape. The left motor is wired to the motor 1 connectors on the Explorer Hat, and the right motor is wired to motor 2 connectors. Note you may have to do a little trial and error on the Explorer HAT “+” and “-” motor connections to get both wheels spinning in a forward direction.

The Explorer HAT Node-Red library is installed by:

 cd $HOME/.node-red
npm install node-red-dashboard 

The Web dashboard presentation is configured in the “dashboard” tab. For this example we create 2 groups: a control group to drive the vehicle, and a light group to turn on the Explorer Pro lights. Use the “+group” button to add a group, and the “edit” to change an existing group.
dash_conf

To control a motor, an “Explorer HAT” node and a dashboard button node are dropped and connected together. All the configuration is done in the button node . The button configure options are:

  • the group the button will appear in (Controls)
  • the size of the button (3×1 = 50% of width and narrow)
  • Topic, motor.one or motor.twois used for motor control
  • Payload, -100 = reverse, 0=stop, 100 = forward

Control_conf

The Explorer HAT has 4 colored LEDs. To toggle the LEDS, the topic is light.color with 1=ON, and 0=OFF . We thought that it would be fun to also add some Web dashboard button to control the colored lights.

light_conf

The Node-Red dashboard user interface is accessed by: ipaddress:1880/UI, so for example 192.168.1.102:1880/ui. Below is a picture that shows the final vehicle logic and the Web dashboard.

 

final_logic2

 

 

 

littleBits/Pi Temperature Monitor

By using littleBits Proto modules it is possible to create Raspberry Pi projects with littleBits components. On this project we created a temperature monitor with a local indication and a remote Web page using Node-Red.

The parts used were:

  • 1 Raspberry Pi 3
  • 1 Explorer Hat (used for Analog Inputs)
  • 2 littleBits Proto bits
  • 1 littleBits Temperature bit
  • 1 littleBits Number bit
  • 1 littleBits Wire bit (optional, used for easier wiring)

The Wiring

To complete the littleBits circuit the first Proto bit was wired with 5V to the VCC and the data connectors. Pi GND was wired to the module’s GND. The second Proto bit had the data pin with to the Explorer HAT analog input 1.

tempcircuit

Node-Red Logic

On the Pi, the following Node-Red nodes were used:

  • Explorer Hat Node – reads the analog input
  • Function Node – only pass on analog input 1
  • Smooth Node – removes noise and jitter
  • Function Node – converts 0-5V to 0-100 C

temp_logic

The logic for the first function node, (to pass only analog input 1), was:

 if (msg.topic == "explorerhat/analog.1"){
return msg;
} 

We added a smooth node to remove noise in the analog input signal. The configuration that we used for the smooth node was:

temp_smooth

The logic for the second function, (to convert the voltage to a temperature), was:

msg.payload= (100/5)*msg.payload;
return msg;

Finally we used a Chart Dashboard node to show the results on a Web page. Our configuration for this was:

temp_gauge

To view the Web page use the URL of : http://the-pi-address:1880/ui

temp_pic_full

littleBits/Pi Internet Radio

The littleBits Proto bit allows littleBits components to be directly to connected to a Raspberry Pi (or Arduino).

The Goal

The goal of this project was to play Internet Radio and use littleBits to:

  • start the music, (and possibily change the music)
  • control the volume
  • use the littleBits speaker

For this project we used:

  • 2 Proto Bits
  • 1 Fork Bit
  • 1 Button Bit
  • 1 Slide Dimmer Bit
  • 1 Speaker Bit
  • 1 Bargraph Bit (optional)
  • 1 Wire Bit (optional)

The Wiring

music_setup

For the littleBits to Pi wiring, the input to the Fork Bit needs to have 5V on both the power and data pins, the GND pin of the Proto Bit is wired to GND on the Pi.

music_circuit

The output on the littleBits Button bit is wired into GPIO 23 on the Pi.

The Logic

For the logic we used Node-Red, Python would have probably been a better choice, but we wanted to see if it could improve our Node-Red skills.

To play Internet music we need to load the Node-Red mpd node:

cd $HOME/.node-red
npm install node-red-contrib-mpd

The Node-Red logic used only 3 nodes:

  • 1 – Raspberry Pi input node, to read button push
  • 1 – Function node, to do some action on the button push
  • 1 – MPD Output node, to play Internet Radio

radio_logic

There are a lot of possible options for what the littleBits button could do. For this example we simply wanted to load an Internet Radio URL, and then start playing. To find Internet Radio stations go to: https://www.internet-radio.com/.

music_func

The function node had a context variable, issetup,  that was used to load the music for the first time and then start playing.

// create an "is setup" variable
var issetup = context.get('issetup')||0;

if (msg.payload == "1") {
// if the setup hasn't been run, add a radio station playlist
if (issetup === 0) {
context.set('issetup',1);
var msg0 = { payload:"clear"};
var msg1 = { payload:"add http://185.33.21.112:11029" };
var msg2 = { payload:"play" };
return [ [ msg0, msg1, msg2] ];
}
}

Pi Node-Red Streetcar

For our streetcar design we wanted to :

  • manually control things with a Web interface on a smart phone, and
  • automatically have the streetcar stop at station, wait, then go in the reverse direction.

For this project we built everything in Lego, with Lego Mindstorm components. The programming was done in Node-Red which was running on a Raspberry Pi.

The Lego Mindstorms EV3 and NXT components can be wired into your Pi (or Arduino) projects by using some custom adapters. If you are brave you could cut one end off of the connector cables. We unfortunately didn’t have any extra cables so went the safe route with the adapters. There are a couple of different adapters that are available we used the breadboard version from Dexter Industries.

Using the following parts we were able to make an automated streetcar :

  • 1 Lego Mindstorms motor
  • 1 Lego Mindstorms touch sensors
  • 3 Lego Mindstorms connector cables
  • 3 Dexter Lego Mindstorms bread board adapter
  • 1 small breadboard
  • 1 Pi 3 (or Pi 2 with a network connection)
  • 1 Pimoroni ExplorerPro Hat
  • 2 long pieces of wire
  • lots of Lego blocks

Streetcar Design

Our goal for the streetcar project was to have two stations, then have the streetcar automatically stop and switch directions at each station.

full_street

Station 1 had the motor, a touch sensor, and the Raspberry Pi.

station1

Station 2 had a pulley wheel, a touch sensor and a small breadboard that wired back to the Pi at station 1. Our pulley string went above the streetcar. We needed to keep the string quite tight so the pulley would not slip.

station2_top1

The Wiring

All of the Lego Mindstorms wiring used the same pins on the left side of the connector. and they are labeled “ANG” and “GND”. We used an ExplorerHat Pro to connect the Lego Mindstorms Motor and touch sensors to the Raspberry Pi. As we mentioned earlier the station 2 touch sensor was wired into a small breadboard and then from there two wires connected it to the ExplorerPro. For our setup station 1 touch sensor was wired on Explorer Pro input 1, and station 2 was on input 2.

circuit

Node-Red Installation

To check that Node-Red is installed and working, go to a Terminal window and enter:

node-red-start &

If you are able to run Node-Red, the next step is to install the Pimoroni ExplorerHat node and a web dashboard node. Depending on your installation you might need to load the Node Package Manager, npm :

sudo apt-get update
sudo apt-get install npm

Then to install the added libraries:

\curl -sS get.pimoroni.com/explorerhat | bash
 cd ~/.node-red
 npm install node-red-contrib-explorerhat
 npm install node-red-dashboard

After you install these library nodes you will need to restart your Pi. Once Node-RED restarts, you use a web browser to build applications. If you are working directly on your Pi, enter 127.0.0.1:1880 in the URL address box of your browser.

Node-Red Manual Web Control

To make a web based manual control program, drag three button nodes from the left node panel onto the center panel. Then wire the button nodes to an ExplorerHat output node.

nr2

Double click on a button node to open an edit window. The edit window allows you to configure the dashboard, labels and button actions. To control the first ExplorerHat motor the topic is motor.one. The payload is between -100 and 100, and this corresponds to full reverse and full forward, with 0 being stopped.

After you have finished all your Node-Red configure click the Deploy button at the top right of your browser window. Deploying will run your program and enable the web dashboards. To access the web dashboards enter: http://your-ip-address:1880/ui. If you are unsure of your IP address go to a terminal window and enter : ifconfig.

screenshot

Node-Red Automatic Control Program

We found the automatic control logic to be a little tricker than the manual logic. Our first step was to see if we could read the Lego Mindstorms touch sensors. For this we connected an ExplorerHAT input node to a debug node. We manually pushed each touch sensor and we used the debug tab to check the results.

debug

To catch when the streetcar hits the touch sensor at station 1 we needed to create a function that looked at the topic explorerhat/input.1. If this topic’s playload is 1 or pushed then the ExplorerHat motor can be stopped by sending a message with the topic of motor.one and the payload=0. A similar function is created for the touch sensor at station 2 except the topic explorerhat/input.2 is monitored.

button1

After the streetcar hits a touch sensor we wanted it to pause, and then move in the opposite direction. A delay node was used for the pause. Following this a function node is used to send a message with a payload of the new speed and direction. For our project station 1 restarted with a speed of -70, and station 2 restarted with a speed of 70 (or +70).

reverse1

Our complete logic with both manual and automatic control is shown below:

full_logic

Using QR Codes

The typical UPC-A barcode is visually represented by strips of bars and spaces, that encode a 12-digit number. A QR code (Quick Response Code) is a matrix barcode that can contain up to 4296 characters.

For Pi or Arduino projects QR codes could be used to document what the module is doing, or “if lost please call…”, or web links.

Create Your Own QR Codes

There are a number of different tools available to create your own QR codes. One of the simplest methods is to use Google Charts, and it is called by:

http://chart.apis.google.com?

The important parameters are:
cht=qr – chart type = qr
chs=x – chart size, and
chl= – the data or URL to encode

An example of encoding “Hello World” in a 100×100 QR would be:

http://chart.apis.google.com/chart?chl=Hello+World&chs=100×100&cht=qr

A simple web form that can be used to create QR codes

 <html>  
 <head>  
  <title>Create QR Codes</title>  
 </head>  
 <body>  
 <h1>Create QR Codes</h1>  
 <form action="http://chart.apis.google.com/chart" method="get">  
      Text to embed in QR Code</br>  
      <textarea name="chl" style="height:100px;width:300px;"></textarea>  
      </br>Image Size :</br>   
      <select name="chs">  
           <option value="100x100">100x100</option>  
           <option value="150x150">150x150</option>  
           <option value="200x200">200x200</option>  
           <option value="250x250">250x250</option>  
           <option value="300x300" selected>300x300</option>  
           <option value="350x350">350x350</option>  
           <option value="400x400">400x400</option>  
           <option value="500x500">500x500</option>  
      </select>  
      <input type="hidden" name="cht" value="qr"></br>  
      <p><input type="submit" value="Create QR Code"></p>  
 </form>  
 </body>  
 </html>  

 

html_code

After the image is generated it can be printed, cut to size and then taped to your equipment. If you have a number of Arduino or Pi modules QR codes could be an easy way to determine what is loaded on each module.

Create an Android QR Reader App

MIT’s AppInventer is a great option for Android smart phones and tablets.

For our application we used the following components:

  • 1 Button – to start QR scanning
  • 1 Textbox – to show QR scan results
  • 1 Button – to call a browser if the QR code is a Web link
  • 1 BarcodeScanner – to turn on the camera and process the QR code
  • 1 ActivityStarter – to launch the web browser

screen

The logic starts by defining the camera to be used for the QR scanning, and setting the ActivityStarter.Action to be a browser (android.intent.action.VIEW).

The BarcodeScanner1.AfterScan block puts the decoded QR data into the textbox. If the QR code starts with “http” then the “Open Link” button is enabled.

logic

Once our custom QR reader app is on our device we can start to customize it to our needs. The picture below shows the basic app reading a 100×100 QR code used on an Arduino project. Some future considerations that could be added to this simple app could things like: recording the geographic location of the device or is the data valid.

scan2

QR Codes and the Internet of Things (IoT)

For projects with a lot of sensors or devices QR codes can be helpful to identify and document what each device is used for. If the device is a source of data then a QR code could link to that specific devices data.

The picture below is an example of a solar powered weather device. The ESP8266 based Arduino module uses MQTT to send data back to a Pi node running Node-Red. The QR code on the side of the enclosure has a link to the Node-Red web page.

outside2