Pi Rover using a Bottle Web Framework

There are a lot of Python web library choices, with each of the libraries offering different features and functions.

For simple Raspberry Pi Web application I was really impressed by the Python Bottle library. In this blog I’d like to document a Raspberry Pi rover project that I did using bottle.

Getting Started

To install the Python bottle library:

pip install bottle

There are some good tutorials for bottle. Probably the most important item is defining a decorator for a URL, and then linking the decorator to a function:

@route('/') # define a decorator for the start page
def my_homefuntion() # call a function for the start page
   return static_file("startpage.htm", root='') # call the start page

@route('/otherpage') # define a decorator for another page 
def my_otherpage_function() # call a function for the start page
   # do some stuff...

For the RaspPi rover I used a low cost car chassis (~$15).

It is not recommended to connect motors directly to Rasp Pi pin, for a few reasons:

  • larger motors require more power that a Pi GPIO pin can supply
  • power surges on motors can damage the Pi hardware
  • forward/backward motor directions require extra hardware
  • GPIO pins will only do ON/OFF, no variable speed settings.

There are a number of Raspberry Pi motor shield that can be used. For this project I used the Pimoroni Explorerhat Pro ($23). The Explorerhat has an excellent Python library that allows you to easily control the motor’s direction and speed.

Web Page

The goal for the web page (bottle1.htm) was to have 5 buttons for the controls and use AJAX to send the action request and then return the action code and display it on the page. The returned action would appear above the buttons ( in the lastcmd  paragraph tag).

Screen_bottle

For this example the button push was sent in the header as a GET request. So a forward button push would be a myaction: forward header item. In previous projects I’ve used POST request with parameters, however I found that header items can make things a little simpler.

<!DOCTYPE html>
<html>
<head> 
<title>Python Bottle Rover</title> 
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="icon" href="data:,"> 
<style>
  html{font-family: Helvetica; display:inline-block; margin: 0px auto; text-align: center;}
  h1{color: #0F3376; padding: 2vh;}p{font-size: 1.5rem;}
  .button{display: inline-block; background-color: #4286f4; 
  border-radius: 4px; color: white; font-size: 30px; width:100%; height: 75px}
  .button2{background-color: green ;width:31%}
  .stop{background-color: red; width:33%}
</style>
</head>
<script>
function sendcmd(thecmd) {
  // send the action as a header item 
  var xhttp = new XMLHttpRequest();
  xhttp.open("GET","/action" , true);
  xhttp.setRequestHeader("myaction", thecmd);
  xhttp.send()
  xhttp.onreadystatechange = function() {
	// Get the response and put on it the screen
	if (this.readyState == 4 ) {	
		document.getElementById("lastcmd").innerHTML = "Last Command:<b>" +xhttp.responseText;
	}
  }
}
</script>
 
<body>
<h2>Python Bottle Rover</h2> 
<p id='lastcmd'></p>
<button onclick="sendcmd('forward')" class="button">FORWARD</button>
<button onclick="sendcmd('left')" class="button button2">LEFT</button>
<button onclick="sendcmd('stop')" class="button stop">STOP</button>
<button onclick="sendcmd('right')" class="button button2" >RIGHT</button>
<button onclick="sendcmd('backward')" class="button button">BACKWARD</button>
  
</body>
</html>

 

Bottle Rover App

For the rover app, there are two URL endpoints. The root (/) which would display the bottle1.htm page, and an action (/action) URL which would only be called from AJAX script when a button was pushed.

For this project the Raspberry Pi ip address was hardcoded into the code, for future projects dynamically getting the ip would be recommend. Also a web port of 8000 was used so as to not conflict with a dedicated web server (like Apache) that could be running on the Pi.

# Bottle2rover.py - web control for a RaspPi rover<span id="mce_SELREST_start" style="overflow:hidden;line-height:0;"></span>
#
from bottle import route, run, static_file, request

# Define RaspPi I/O pins
import explorerhat

# Send Action to Control Rover
def rover(action):
  if action == "forward":
    explorerhat.motor.one.speed(100)
    explorerhat.motor.two.speed(100)
  if action == "left":
    explorerhat.motor.one.speed(100)
    explorerhat.motor.two.speed(0)
  if action == "right":
    explorerhat.motor.one.speed(0)
    explorerhat.motor.two.speed(100)
  if action == "stop":
    explorerhat.motor.one.speed(0)
    explorerhat.motor.two.speed(0)
  if action == "backward":
    explorerhat.motor.one.speed(-50)
    explorerhat.motor.two.speed(-50)

# use decorators to link the function to a url
@route('/')
def server_static():
  return static_file("bottle1.htm", root='')
# Process an AJAX GET request, pass the action to the rocket launcher code
@route('/action')
def get_action():
  action = request.headers.get('myaction')
  print("Requested action: " + action)
  rover(action)
  return request.headers.get('myaction')

# Adjust to your required IP and port number
run(host = '192.168.0.106', port=8000, debug=False)

Final Comments

I was happily surprised how easy it was to get a Python bottle web app running. The bottle documentation was straightforward and I found that the code was quite lean.

Get Jokes and Quotes

I was trying to get a database of recent jokes and quotes, unfortunately there aren’t a lot of really good downloadable sources that have new and relevant material.

Reddit is a social media site that has a lot of potential for building databases or lists of recent jokes and quotes.

In this blog I wanted to document how I created a list of recent jokes and quotes using the Python reddit library (praw) . I also included some filtering to help remove bad items.

Reddit

Reddit is a social media source that is free to use. To pull information from Reddit you will need to create an account and get API client ID and secret. To do this go to: https://www.reddit.com/prefs/apps/ and select edit in the developed applications area.

reddit_api_info

The Reddit Python library is called Praw, and it is installed by:

pip install praw

To use the Python Reddit library you will need:

  • your username
  • your password
  • your client ID and client secret

Reddit has a wide list of categories and once a category is selected you can sort the list by:  new, hot and trending.

reddit_jokes

Python Joke Example

An example of using Python to get the “hot” dad jokes from Reddit is below. For this example I included a bad_keywords list. Some trial and error will be required to remove some returned items

 # Python Reddit Example # Get top 10 dad jokes  
 # Some filtering is added to remove bad items   
   
 import praw  
 import re # use this is filter out bad items  
   
 # remove items with these words in them (could include swear words)  
 bad_keywords = ['edit','remove','delete', 'repost','this sub']  
   
 reddit = praw.Reddit(client_id='xQsMfaHxxxxxxx',  
            client_secret='X8r62koQgVxxxxxxxx',  
            user_agent='myreddit', username='yourusername', password='xxxxxxx')  
                             
 i=0                            
 for submission in reddit.subreddit('dadjokes').hot(limit=10):  
     thestring = submission.title + " " + submission.selftext  
     if not re.compile('|'.join(bad_keywords),re.IGNORECASE).search(thestring):  
         i += 1  
         print(i,submission.title,"..." submission.selftext )  
   
   

 

The output will look something like:

1 What’s Beethoven doing in his grave ... De-composing
2 Why can’t Swiss cheese be part of a fat-free diet? ... It’s made with hole milk.
3 People always wonder how I come up with flaccid penis jokes so easily and I just respond back with... ... It's not that hard.
4 2020 is going to be a great year. ... I can see it so clearly.
5 I got kicked out of karaoke after singing “Danger Zone” nine times in a row. ... Too many Loggins attempts.
6 What did one snowman say to the other snowman? ... "Do you smell carrots?"
7 The store near me is having a sale on batteries. ... If you buy two packs, they'll throw in a pack of dead ones, free of charge.
8 Mr Ed just moved next door to me a few days ago. ... We’re neighbors now.

There are a number of other joke categories such as : yomamajokes, jokes, cleanjokes, greyjokes…

The reddit.subreddit object can have .hot, .new and .top calls.

For quotes see categories such as : quotes, showerthoughts

 

 

Same Code for Python GUI and Web Apps

The Python PySimpleGUI project has two main goals:

  • A simpler method for creating graphical interfaces, and
  • Common code for Tkinter, QT, xW and Web graphics

I feel comfortable doing my own Tkinter and Web interfaces, but common code for both is very cool and it could be very useful for Rasp Pi applications. However things didn’t work “out of the box”, so this blog will look at some workarounds and issues.

A Simple Example

If you are used to coding in QT or xW PySimple is absolutely easier to use.

PySimpleGUI has some defined graphic objects (like Text or Button) and the screen placement is defined by how they are grouped with [ ] brackets. For example two objects in a [ ] bracket puts the two objects on the same line. 

If you’re a Tkinter user PySimpleGUI may seem a little more cumbersome in it’s layout design. (I find Tkinter’s grid methods to be a superior layout approach).

For my first example I used the published example and I added an option for the graphic method (tkinter, Qt, Wx and Web):

 import sys, random, time  
   
 mode = "tkinter"  
 # Check for command line arguments   
 if len(sys.argv) > 1: # if there is use the Web Interface  
   if sys.argv[1] == 'web':  
     import PySimpleGUIWeb as sg  
     mode = "Web"  
   elif sys.argv[1] == 'wx':  
     import PySimpleGUIWx as sg  
     mode = "Wx"  
   elif sys.argv[1] == 'qt':  
     import PySimpleGUIQt as sg  
     mode = "Qt"  
   else:  
     import PySimpleGUI as sg  
   
 else: # if no arguments use the standard GUI  
   import PySimpleGUI as sg  
   
 # Basic example from PySimpleGUI
   
 sg.change_look_and_feel('DarkAmber')  # Add a touch of color  
 # All the stuff inside your window.  
 layout = [ [sg.Text('Some text on Row 1')],  
       [sg.Text('Enter something on Row 2'), sg.InputText()],  
       [sg.Button('Ok'), sg.Button('Cancel')] ]  
   
 # Create the Window  
 window = sg.Window('PySimpleGUI ' + mode , layout)  
 # Event Loop to process "events" and get the "values" of the inputs  
 while True:  
   event, values = window.read()  
   if event in (None, 'Cancel'):  # if user closes window or clicks cancel  
     break  
   print('You entered ', values[0])  
   
 window.close()  
 print('Program terminating normally')  
   

The output for the different graphic methods looks incredibly similar for this example:

GUI_wxGUI_webGUI_tkGUI_qt

It’s important to note that PySimpleGUI is still under development so many of the features will be in transition. If you stick to basic functions like: buttons, images and text you should be good.

I found that the default Tkinter version to be very solid, and the other versions would complain on some of the added features such as: frames, sliders, and progressbars.

A Realtime Update Example

For my next example I wanted to do a Rasp Pi type example with some simulated values from a temperature sensor.

To write back to a graphic object:

  • define a key name when the object is defined (key = “myojbname”)
  • use:  window[‘myojbname’]( new_value) to update the object
 import sys, random, time  
   
 mode = "tkinter"  
 # Check for command line arguments   
 if len(sys.argv) > 1: # if there is use the Web Interface  
   if sys.argv[1] == 'web':  
     import PySimpleGUIWeb as sg  
     mode = "Web"  
   elif sys.argv[1] == 'wx':  
     import PySimpleGUIWx as sg  
     mode = "Wx"  
   elif sys.argv[1] == 'qt':  
     import PySimpleGUIQt as sg  
     mode = "Qt"  
   else:  
     import PySimpleGUI as sg  
   
 else: # if no arguments use the standard GUI  
   import PySimpleGUI as sg  
   
 # Basic example of PSGWeb  
   
 def main():  
   sg.change_look_and_feel('LightGrey')  
   dataframe = [  
     [sg.Text('Temperature (C):',size=(12,2)),  
     sg.Text(' ', font='Courier 48', text_color='red', key='degC')],  
     [sg.Text('Humidity (%)  :',size=(12,2)),  
     sg.Text(' ', font='Courier 48', text_color='red', key='humid')],  
       
   ]  
   layout = [  
     [sg.Image(filename = "dht11.png"),sg.Frame("DHT11 Sensor", dataframe,font='Any 12', title_color='blue')]  
     ]  
     
   if mode == "web":  # Note: customization on the Web interface
     window = sg.Window('Pi Weather Data ' + mode, layout,web_ip='192.168.0.107', web_port = 8888, web_start_browser=False, disable_close=True)  
   else:  
     window = sg.Window('Pi Weather Data ' + mode, layout)  
     
   while True:  
     event, values = window.read(timeout=10)  
     temp_degC = random.randint(20,30)  
     humidity = random.randint(0,100)  
     window['degC']( temp_degC)  
     window['humid'](humidity)  
     time.sleep(1)  
       
   window.close()  
   
 main()  
 print('Program terminating normally')  
   

The Wx code would not run, and the development team has commented on compatibility issues that they are having with Wx so future support may be dropped.

The Tkinter and Qt, but for this example the Web presentation dropped the frame outline.

GUI2_qtGUI2_tkGUI2_web

PySimpleGUIWeb

The PySimpleGUIWeb project is based on the Remi Project which defines graphics objects in an HTML/Web environment.

One big difference that I found between the Remi project and PySimpleGUIWeb is that Remi supports callbacks. I found that callbacks are extremely useful if you are trying to mix reads and writes in the same application. PySimpleGUI uses a read to get user input but this gets confusing if you are using a timer for writing new data to the GUI.

The PySimpleGUIWeb library by default was missing some key documentation. I found that “out of the box” it wasn’t usable for my applications . However everything that I needed was in the Window class it just wasn’t clearly documented.

The following web features can be controlled:

  • web_ip=’xx.xx.xx.xx’ , default is localhost (127.0.0.1), not good for remote connections.
  • web_port= xxxx , default is a random port id. Again not useful for remote connections.
  • web_start_browser=False, default a web browser is launched (not useful for SSH).
  • disable_close=True , default closes the app when the web browser closes.

An example to open a Web connection (not local) that doesn’t auto-open a browser and stays open would be:

window = sg.Window('Pi Weather Data ',  layout,web_ip='192.168.0.107', web_port = 8888, web_start_browser=False, disable_close=True)

Final Thoughts

I like the concept of the same code being used on both a Tkinter and a Web  app. I believe that this has a lot of potential. However at this point only the simplest features are available in the Web, so I’d rather use a Python Web framework like Bottle.

I really like some of the concepts of PySimpleGUI but I think that understanding and using the standard Tkinter allows you more flexibility and it lets you include add-in modules like Tk_tools.

 

Pi Appliance

My goal was to make a Pi kitchen appliance that shows me the key things that I want to see and music I want to listen to while I’m getting my morning coffee. For this project I used a Rasp Pi with 2.8″ TFT touchscreen. These screens start at a round $15.

People’s morning interests will vary so in this blog I just wanted to highlight some of the issues that I needed to worked through. For me the main stumbling blocks were:

  • Hiding the top Rasp Pi menu bar
  • Creating a GUI that uses the full screen
  • Getting weather data
  • scraping web pages to extract what I need

Getting Started

There are some great Raspberry Pi TFT screens that come with buttons and cases. You will need to look at the documentation that comes with your screen, but a good reference is: https://learn.adafruit.com/adafruit-pitft-28-inch-resistive-touchscreen-display-raspberry-pitft_case

For my project I simply used some of my kids Lego blocks.

pi_kitch2

Remove the Pi Menu Bar

The Pi TFT screen isn’t super large, so I wanted to remove the Pi menu bar and run my application at full size.

tft_w_menu

To remove the menu bar tweek two files. First:

sudo nano /etc/xdg/lxsession/LXDE-pi/autostart

Comment out the line  (with #) :

@lxpanel --profile LXDE

Then do the same for:

nano /home/pi/.config/lxsession/LXDE-pi/autostart

After this reboot the system.

Create a Full Size App

There are a multitude of choices for a screen layout. I was looking for lines of text, with maybe the bottom line used for buttons. I found that 7 lines was a reasonable fit. To remove the Python Tkinter title I positioned the top of the screen above the physical screen position (-30 instead of 0).


# My Kitchen Appliance App
#
import urllib.request as urllib2
import tkinter as Tkinter
from tkinter.ttk import *

from tkinter.font import Font
from tkinter import messagebox
top = Tkinter.Tk()
top.title("My Kitchen Appliance")
top.geometry("320x240+-5+-30") # set screen size, left (-5) and top (-30)
top.resizable(False, False)
top.details_expanded = False

#Define the buttons
myfont = Font(family="Times New Roman Bold",size= 12) # Should try a few more sizes

tft_rows = 7 # try 7 rows of buttons
tftbutton = ['' for i in range(tft_rows)]
for i in range(tft_rows):
    tftbutton[i] = Tkinter.Button(top, text = "Line " + str(i+1), fg = "blue", bg = "white", anchor="w", width= 35, height= 1,font=myfont).grid(row=(i+1),column=1) # a buttpn arra

top.mainloop()

The Python GUI will look like this:

tft_7bttns

Get Weather Data

There are a number of good weather API’s. I used OpenWeather because I can use it in variety of apps like Node-Red. OpenWeather has a free user API but you should login and get an appid.

A Python example to get some current weather data for a city:


# get Open Weather (REST API) data
import requests

# api-endpoint

URL = "https://openweathermap.org/data/2.5/weather?q="
mycity = "burlington,CA"
myappid = "&appid=b6907d289e10d714a6e88b30761fae22"
# sending get request and saving the response as response object
fullURL = URL + mycity + myappid
r = requests.get(fullURL)

# extracting data in json format
data = r.json()

print (data)

# Check out the structure
#for index, value in enumerate(data):
# print(index, value)

# Show some weather data
print (data['weather'][0]['description'])
print (data['weather'][0]['main'])
print (str(int(data['main']['temp'])) + " C")
# convert wind speed from meters/sec to kph
print (str((data['wind']['speed'] * 3.6)) + " kph")

This code will give output such as:

$Python3 burlweather.py
{'coord': {'lon': -79.8, 'lat': 43.32}, 'weather': [{'id': 803, 'main': 
'Clouds', 'description': 'broken clouds', 'icon': '04n'}], 'base': 
'stations', 'main': {'temp': 5.81, 'pressure': 1014, 'humidity': 93, 
'temp_min': 3.33, 'temp_max': 7.78}, 'visibility': 24140, 'wind': 
{'speed': 2.1, 'deg': 50}, 'clouds': {'all': 75}, 'dt': 1574816701,
 'sys': {'type': 1, 'id': 818, 'country': 'CA', 'sunrise': 1574771158, 
'sunset': 1574804839}, 'timezone': -18000, 'id': 5911592, 'name': 'Burlington', 'cod': 200}
broken clouds
Clouds
5 C
7 kph

Scraping Web Pages

I wasn’t able to find an API for all the things I was after, so I need to scrape web pages. The Python Beautiful Soup library is a great for finding and grabbing stuff on web pages. To install it:

$ apt-get install python-bs4 (for Python 2)

$ apt-get install python3-bs4 (for Python 3)

I had an example where I wanted to find the ski lifts and runs open. I had the Web page but I needed to search the ugly HTML code.

ski_bs0

ski_bs

In the HTML code I found that the lift and run information is contained in a <p class=“open value” tag. Beautiful Soup allows you to make searches based on attributes. The results can be HTML code or the .text property will return the results as simple text (no HTML code).

The following Python code would search my URL and extract the number of lifts open:


$ python
Python 3.7.4
Type "help", "copyright", "credits" or "license" for more information.
>>> import urllib.request as urllib2
>>> from bs4 import BeautifulSoup
>>> theurl = 'https://www.onthesnow.ca/ontario/blue-mountain/skireport.html'
>>> page = urllib2.urlopen(theurl)
>>> soup = BeautifulSoup(page, 'html.parser')
>>> liftopen = soup.find("p", attrs={"class":"open value"})
>>> liftopen.text
'2 of 11'

Final Comments

There are a ton of different “Pi Appliance” applications that could be done. I hope that some of these hints that I’ve documented are helpful.

pi_kitch1

Arduino Yún for IoT

There are some great Internet of Things hardware platforms, such as Raspberry Pi’s, ESP-32 based Arduino modules, Particle and Beaglebone to name just a few. Each of these systems have their strengths and weakness. Some are strong on the hardware side, like the Arduino modules, and others excel on the programming side like the Raspberry Pi.  

The Yún is somewhat unique in that it’s a module with two processors, one that supports standard Arduino programming and a second processor that supports Linux and the OpenWrt wireless stack. The Yún ($59) has an Arduino Uno form factor and there are clones like the LinkIt Smart 7688 Duo ($18) in an Arduino Nano form factor.

yun_overview

In this blog I wanted to document some of key feature and functions that I worked through, namely:

  • moving file – scp and ftp
  • Python bridging to Arduino
  • uhttpd Web Server – with Python CGI
  • Yún REST API
  • MQTT
  • Yún mailbox

Yún Overview

The Yún, now in revision 2, seems to have been somewhat overlooked because of the all the low cost ESP-8266 and ESP32 based Arduino modules starting around $2.

Some the interesting features of the Yún include:

  • Arduino code can launch and get feedback from Linux apps
  • A bridge library allows Linux programs and Arduino to share data
  • Arduino libraries for:
    • Web client
    • Web server
    • Mailbox to Linux
  • Yún has a lightweight web server, uhttpd, that can be used to Python, PHP, Lua CGI web programs
  • Yún has a read/write REST API web service

Getting Started

The Arduino side of the Yún is available “out of the box” like any other Arduino module when you connect a USB cable into the module.

The Linux side however requires some configuration. Please see one of the guides on the Linux setup. Once your module is connected to your network, the Yun webserver can be used to configure features and add software components.

yun_software1

Another option for loading software is to use the opkg package manager from an SSH connection.

yun_opkg

So for example to install nano, the simple text editor, enter:

 opkg install nano

Moving File and Working in OpenWrt Linux

The OpenWrt Linux isn’t loaded with with an X-windows environment and this means that you can not run idle or leafpad etc. to do easy editing of program files. Nano is a good command line text editor but it’s not the same as a windows based editor.

To move files between a PC and OpenWrt you have some options. The two that I like are:

  • scp – secure copy, this is built in both OpenWrt and Microsoft Window 10
  • ftp – file transfer protocol. Needs to be installed in OpenWrt.

There are a few ftp servers that could be installed in OpenWrt, vsftp is a lightweight option and it can be installed by:

opkg update
opkg install vsftpd

Once vsftpd is installed it needs to be enabled, this can be done from the command line or via the web interface.

yun_ftp_start.png

Yún Bridge

The Yun Arduino bridge library allow variables to be passed between the Arduino code and a Python program. Below is an example that writes two random variables available, and it creates a “bridge1” variable that can be written from the Python side.

// Simple Yun Bridge Example
//

#include <Bridge.h>
// create a bridge variable to get remote data
char bridge_Value[10];

void setup()
{
    Bridge.begin();     // this launches /usr/bin/run-bride on Linino
}

void loop()
{    
    // create 2 random bridge values, that are sourced from the Arduino
    Bridge.put("random1", String(random(1, 100)));
    Bridge.put("random2", String(random(1, 100)));
    // Called the bridge value "bridge1". This is the name used on the Python side
    Bridge.get("bridge1", bridge_Value, 6);
    delay(1000);  
}

An example to read/write in Python:


#!/usr/bin/python

import sys

sys.path.insert(0, '/usr/lib/python2.7/bridge/')

from bridgeclient import BridgeClient as bridgeclient
value = bridgeclient()

message = value.get("random1") # get a value from Arduino

print "Random1: ", message

value.put("bridge1","1111")  # set a value to Arduino

Yún uhttpd web server

The uhttp web server is used for Yun setup and configuration. This web server can also be used to for custom static pages and user web apps. To view/modify the web server settings:

nano /etc/config/uhttpd

Within this config file, you can enable custom web applications by defining an interpreter:

# List of extension->interpreter mappings.
# Files with an associated interpreter can
# be called outside of the CGI prefix and do
# not need to be executable.
# list interpreter ".php=/usr/bin/php-cgi"
# list interpreter ".cgi=/usr/bin/perl"
list interpreter ".py=/usr/bin/python

# Lua url prefix and handler script.
# Lua support is disabled if no prefix given.
# option lua_prefix /luci
# option lua_handler /usr/lib/lua/luci/sgi/uhttpd.lua

The default directory for user programs is: /www/cgi-bin

Python CGI – Get Values

To read the Arduino bridge values in a Python CGI program, add a file to the /www/cgi-bin directory. For my example I called the file p1.py :


#!/usr/bin/python

import sys
import cgi

sys.path.insert(0, '/usr/lib/python2.7/bridge/')

from bridgeclient import BridgeClient as bridgeclient
value = bridgeclient()

print "Content-type:text/html\r\n\r\n"
print '<html>'
print '<head>'
print '<title>Python CGI Bridge</title>'
print '</head>'
print '<body>'
print '<h2>Python CGI Bridge</h2>'
print 'Random Value1: ' + value.get("random1")
print 'Random Value2: ' + value.get("random2")
print '</body>'
print '</html>'

To run the python script on the web page you will need to change the file right to executable:

chmod +x p1.py

You can debug and see output from the command line.


root@yun1:/www/cgi-bin# ./p1.py
Content-type:text/html

<html>
<head>
<title>Python CGI Bridge</title>
</head>
<body>
<h2>Python CGI Bridge</h2>
Random Value1: 13
Random Value2: 24
</body>
</html>

If the output looks good, try the app from the Web page:

CGI_bridge1

Python CGI – Put Values

There are a number of methods that can be used to send user input from a web page. A simple approach is to use a form. The form data can be read from the cgi.FieldStorage object, using a form.getvalue() call.

#!/usr/bin/python

# Import modules for CGI handling
import cgi
import sys

sys.path.insert(0, '/usr/lib/python2.7/bridge/')
from bridgeclient import BridgeClient as bridgeclient
value = bridgeclient()

# Create instance of FieldStorage
form = cgi.FieldStorage()

# Get data from fields
bridge1 = form.getvalue('bridge1')
if bridge1 != "" :
    value.put("bridge1",bridge1)


print "Content-type:text/html\r\n\r\n"
print """
<html>
<head>
<title>Python CGI - Put Bridge Value</title>
</head>
<body>
<h2>Python CGI Form - Put Bridge Value</h2>
<form action = "/cgi-bin/p2.py" method = "post">
Enter BRIDGE1 value: <input type = "text" name = "bridge1"><br />

<input type = "submit" value = "Submit" />
</form>
</body>
</html>"""

 

The web page will call itself when the submit button is pressed.

CGI_bridge2

Yún REST API

The Yún REST API is a web service that allow remote users and web browsers to view and set bridge values. I found the REST API to be a good tool for testing my Web CGI and Python applications

To view all bridge variables enter: http://yourYun_IP/data/get

yun_rest_1

To get a specific bridge value enter:  http://yourYun_IP/data/get/my_bridge_value

yun_rest_2

To put a bridge value enter: http://yourYun_IP/data/put/my_bridge_value/value 

yun_rest_3

IoT Connections – MQTT

For Internet of Things (IoT) projects you need to pass data from the Arduino and some server. The communications and the server would be something like MQTT or Redis.

The Yún does not have direct access to the Wifi or ethernet port so the standard Arduino libraries for MQTT or Redis etc. will not work. An alternative approach is load the protocol’s command line client on the Linux side and then Arduino can shell out to the Linux tool.

For example to load the  Mosquitto MQTT command line tools:

opkg update
opkg install mosquitto-client

To test MQTT publishing to a topic (mytag1) with a message of 249 on remote client (192.168.0.116) :

mosquitto_pub -h 192.168.0.116 -u username -P password -t mytag1 -m 249

To remotely subscribe to

mosquitto_sub -h 192.168.0.116 -u username -P password -t mytag1

An example of sending out four MQTT messages in Arduino:

/*
Shell out to pass values to a MQTT command line pub
*/
#include <Process.h>

void setup() {
  Bridge.begin();	// Initialize the Bridge
  Serial.begin(9600);	// Initialize the Serial

  // Wait until a Serial Monitor is connected.
  while (!SerialUSB);
}

void loop() {
  Process p;
  String thecmd;
  String strval = String( random(0,100));
  // create a string with host, username and password, -t is for the topic
  String theparams = "-h 192.168.0.116 -u pete -P pete -t ";
  int numtopics = 4;
  String topics[4] = {"tag1","tag2","tag3","tag4"};

  for (int i=0; i < numtopics ; i++) {
    strval = String( (i*100) + random(1,99)); // create a random value - 0,100+,200+,300+
    thecmd = "mosquitto_pub " + theparams + topics[i] + " -m " + strval;
    Serial.println(thecmd);
    p.runShellCommand(thecmd);
    // do nothing until the process finishes, so you get the whole output:
    while (p.running());
  }
  // Wait 5 seconds and repeat
  delay(5000);  // wait 5 seconds before you do it again
}

It is also possible to create some bridge variables and pass them to a Python program that could do the MQTT communications.

Yún Mailbox

At present the mailbox only works in one direction, and this into the Arduino. Both the REST web interface and Python have writing functionality but no read capabilities (on the forums this has been identified, so a future revision may add this).

To write using REST:

http://yun_ip/mailbox/mymessagetext

To write using Python:


import sys
sys.path.insert(0, '/usr/lib/python2.7/bridge')
from bridgeclient import BridgeClient
client = BridgeClient()
client.mailbox("my_message")

The Arduino code to read message:

// Mailbox Read Example
//
#include <Mailbox.h>

void setup() {

  // Initialize Bridge and Mailbox
  Bridge.begin();
  Mailbox.begin();

  // Initialize Serial
  SerialUSB.begin(9600);

  // Wait until a Serial Monitor is connected.
  while (!SerialUSB);
  SerialUSB.println("Mailbox Read Message\n");
}

void loop() {
  String message;

  // if there is a message in the Mailbox
  if (Mailbox.messageAvailable()) {
    // read all the messages present in the queue
    while (Mailbox.messageAvailable()) {
      Mailbox.readMessage(message);
      SerialUSB.println(message);
    }

    SerialUSB.println("Waiting 10 seconds before checking the Mailbox again");
  }
  // wait 30 seconds
  delay(10000);
}

I’m not totally sure when I’d use a mailbox. The mailbox is a generic message and it’s not queued (only 1 message) so I think that using the standard bridging of values with get/put is more useful.

Final Comments

The Yun is missing a lot of networking libraries that are available with the ESP-8266 and ESP32 family of Arduino modules. In some cases like with MQTT that was a good Linux command line tool that could be used, but in cases like where you want to connect to a Redis server, you might have some challenges.

I really liked Yun’s built in uhttpd web server, this is far superior to the ESP-8266 Arduino web server library calls.

I found that putting logic into a combination of Python and Arduino could be a little confusing, but for projects with a lot of text or json data using Python would be a real plus. Also for projects where multitasking is required use the Linux process would be ideal.

Pi with Neopixels/Simulated Neopixels

Neopixels are addressable full-colour RGB LEDs that come in a variety of different arrangements. Ranging from single LEDs, to matrix arrays and a variety of sewable components that can be used on wearable products.

dif_neopixels

Neopixels were originally made available for Arduino projects, but now there are also Python libraries for Raspberry Pi’s.

In this blog I will be looking at setting up neopixels components on Raspberry Pi’s, and then I will show some “soft” neopixel layouts using the Python Tkinter graphic library.

Getting Started

To load the Raspberry Pi neopixel libary comes from the nice people at Adafruit, and it is loaded by:

sudo pip3 install rpi_ws281x adafruit-circuitpython-neopixel

It is important to note that neopixels can draw a lot of power so consider looking at using external 5V power for projects with a lot of LEDs. The LED power consumption is based on:

  • How many neopixel LEDs are lit at one time, and
  • What the intensity of the LEDs is.

A few other import points are:

  • not all neopixel strips are the same. Different strips will vary greatly from the LED intensity, and more importantly on the RGB vs. GRB addressing.
  • NeoPixels must be connected to D10, D12, D18 or D21 to work
  • For NeoPixels to work on Raspberry Pi, you must run the code as root

The neopixels are wired with 3 pins : 5V (VCC), GND and signal in. The default signal in wires to Pi pin 18. Neopixel component can be connected in series with data in and out connectors.

data_in_out

Below is an example that will set all the LEDs to a light magenta and then it will cycle one LED to a brighter RED. The overall neopixel string has a 10% brightness.


# Python neopixel example to cycle an LEDs

import board
import neopixel
import time

ORDER = neopixel.RGB  # or neopixel.GRB
numpixels = 12

# Create a pixel object with 12 pixels and low intensity
pixels = neopixel.NeoPixel(board.D18,numpixels , brightness=0.10, auto_write=True, pixel_order=ORDER)
while True:
for i in range(numpixels):
   pixels.fill((10, 0, 40)) # fill all pixels in light magenta
   pixels[i] = (80,0,0) # fill one pixel in brighter red
   time.sleep(1)

Depending on the type and manufacturer of the neopixels the result will look a little different. Some trial and error testing will be required to determine if the strips are RGB or GRB.

 

Simulated Neopixels

If you don’t have neopixels or if what to simulate neopixels then the Python Tkinter graphic library can be used to create a variety of different arrangements. For my testing I create two arrangements: a strip and a matrix.

The important things that I learned was how to create a array object that could simulate the neopixel object. To do this in Python:


import tkinter as tk

root = tk.Tk()
root.title("Soft NeoPixel Strip")

numleds = 25

# Create an array that can be used later in Tkinter

ledstrip = ['' for i in range(numleds)]

for i in range(numleds):
   ledstrip[i] = tk.Label(root,relief='raised',width=3 ) # a label array
   ledstrip[i].grid(row = 0, column = i) # position the labels is a horizontal row
root.mainloop()

Simulated Strip Neopixel

Below is an example of a soft “strip” neopixel application with a demo function.

py_neo_Strip

# Python Neopixel Single Strip Presentation
#
import tkinter as tk

numleds = 25

theled = 0

def stringdemo():
    # move a coloured LED around the string
    global theled
    ledstrip[theled].configure(background= 'white')
    theled = theled + 1
    if theled >= numleds:
        theled = 0
    ledstrip[theled].configure(background= 'sky blue')
    root.after(500, stringdemo)
    
root = tk.Tk()
root.title("Soft NeoPixel Strip")

# create an LED object 
ledstrip = ['' for i in range(numleds)]

# put the LED object into a horizontal strip
for i in range(numleds):
    ledstrip[i] = tk.Label(root,width=2,height=1,relief='raised',background = 'white')
    ledstrip[i].grid(row = 0, column = (i+1))

root.after(500, stringdemo) #start a demo

root.mainloop()

Simulated Matrix Neopixels

Below is an example of a soft matrix neopixel application.

py_neo_Matrix

# Python Neopixel Matrix Presentation
#
import tkinter as tk

numleds = 100
rowcnt = 10
colcnt = int (numleds/rowcnt)

theled = 0

def stringdemo():
    # move a coloured LED around the string
    global theled
    ledstrip[theled].configure(background= 'dark gray')
    theled = theled + 1
    if theled >= numleds:
        theled = 0
    ledstrip[theled].configure(background= 'red')
    root.after(500, stringdemo)
    
    
root = tk.Tk()
root.title("Soft NeoPixel Matrix")

# create LED object
ledstrip = ['' for i in range(numleds)]

# put the LED object into a grid
for i in range(rowcnt):
    for j in range(colcnt):
        ledstrip[theled] = tk.Label(root,width=4,height=2,relief='raised',background = 'dark gray')
        ledstrip[theled].grid(row = i, column = j)
        theled = theled + 1

theled = 0 #reset the led index for the demo
root.after(500, stringdemo)

root.mainloop()

Summary

Neopixels can be used on custom lighting applicatons, for example I used them on a water fountain project.

Given a choice I would recommend using Arduino hardware over the Raspberry Pi hardware for neopixel projects. I found that the Arduino neopixel library to be much more stable and considerably faster than the Pi version.

Pi Thermometer using Python Turtles

Python Turtles are a great way to start kids in programming. Turtles offer a simple step-by-step graphical presentation that has tons of tutorials and examples.

Turtles can also be used on Raspberry Pi projects. In this blog I wanted to look at a Turtle example that reads a temperature sensor and graphically shows the result as an “old style” thermometer.

Getting Started

Python Turtles is probably already  loaded on your system, if not enter:

pip install turtles

The turtle library opens a graphic screen with the very center of the screen being (0,0). This is a little different than many other graphic systems (like PyGame) where the top left  is (0,0).

Different turtle objects can be defined and moved around the screen. A useful feature of turtles is that you can clear all the drawing from one turtle without effecting what the other turtles have done. (Note: this is useful in this thermometer example where we can have a static background turtle and a dynamic turtle that updates with new information).

Below is an example with 3 turtles. The first turtle (t1) is set to red and then moved forward, left, forward and then sent home. The second turtle (t2) is set to purple and given a turtle symbol. The third turtle (t3) is set to green and then moved to a position and a thick circle is drawn.


from turtle import *

setup(500, 400)
Screen()
title(" 3 Turtles")

# First red turtle goes forward, left, forward and back home
t1=Turtle()
t1.color("red")
t1.forward(100)
t1.left(90)
t1.forward(100)
t1.home()

# Second purple turtle has a turtle shape
t2=Turtle()
t2.shape("turtle")
t2.color("purple")
t2.right(45)
t2.forward(100)
t2.left(90)
t2.forward(100)

# Third green turtle goes to a location and makes a thick circle
t3=Turtle()
t3.color("green")
t3.pensize(10)
t3.up()
t3.goto(-100,-10)
t3.down()
t3.circle(80)

turtles1

Drawing an “Old Style” Thermometer

For this project we wanted to draw an “old style” mercury thermometer, with a bulb of red mercury at the bottom and a tube above it.

therm_bg

Using the simple turtle commands like : move, left, right, forward etc. is great to learn but it can be awkward for more difficult drawings.

A more efficient approach is to define an array of x,y coordinates and then move to each position in the array. For example the upper tube can be drawn by:


# Define an array of x,y coordinates for the top tube
outline = ((0,-50),(25,-50),(25,210),(-25,210),(-25,-50),(0,-50))
for pos in outline: # move to each tube x,y point
       thermo.goto(pos)
       thermo.pendown()

Circles are created using a turtle.circle(width) command. To fill an object or a group of objects a turtle.begin_fill() and a turtle.end_fill() set of command is used.

For our example the filled circle for the bulb is created by:


# put the pen up and move to the circle starting
thermo.penup()
thermo.goto(0,-137)
thermo.pendown()
thermo.pensize(5)
thermo.color("black","red")
# draw the circle with fill
thermo.begin_fill()
thermo.circle(50)
thermo.end_fill()

The complete code to draw the complete thermometer background would be:


# Create a background for an "old style" thermometer
from turtle import Turtle,Screen, mainloop
import random, time

# Define a Turtle object
thermo = Turtle()
thermo.penup()
thermo.hideturtle()
thermo.pensize(5)

# Define an array of x,y coordinates for the top tube
outline = ((0,-50),(25,-50),(25,210),(-25,210),(-25,-50),(0,-50))
for pos in outline: # move to each tube x,y point
       thermo.goto(pos)
       thermo.pendown()
# put the pen up and move to the circle starting
thermo.penup()
thermo.goto(0,-137)
thermo.pendown()
thermo.pensize(5)
thermo.color("black","red")
# draw the circle with fill
thermo.begin_fill()
thermo.circle(50)
thermo.end_fill()

mainloop()

Raspberry Pi Hardware Setup

There are a number of different temperature sensors that can be used. For our example we used a low cost ($5) DHT11 temperature/humidity sensor. The DHT11 sensor that we used had 3 pins, (Signal, 5V and GND), and we wired the Signal pin to the Pi physical pin 7.

DHT11-Wiring-Diagram

There is a DHT temperature/sensor Python library that is installed by:

sudo pip install Adafruit_DHT

A Python DHT test program would be:


#!/usr/bin/python
import sys
import Adafruit_DHT

sensor_type = 11 # sensor type could also be 22, for DHT22

dht_pin = 4 # Note: BCM pin 4 = physical pin 7

humidity, temperature = Adafruit_DHT.read_retry(sensor_type, dht_pin)

print( "Temp: ", temperature, " deg C")

print( "humidity: ", humidity, " %")

Turtle Thermometer

Now for the final project we can start pulling things together.

For the thermometer project we used 2 turtles, a static background turtle (thermo) and a dynamic turtle (bar). The bar turtle is cleared and redrawn in the drawbar() function.

A screen object wn is used to resize the window and add a title.

For testing a random integer can be used. This is also useful for checking the 0-40C range of the bar.

The full code and an screen shot are below:


from turtle import Turtle,Screen, mainloop
import random, time
import Adafruit_DHT

# Update the temperature bar height and value
def drawbar(temp):
       top = (-50 + 260 * temp/40)
       boutline = ((0,-50),(20,-50),(20,top),(-20,top),(-20,-50),(0,-50))
       bar.penup()
       bar.clear()  # clear the old bar and text
       bar.begin_fill()
       for pos in boutline:
              bar.goto(pos)
       bar.end_fill()
       bar.goto(30,top)
       bar.write(str(temp) + " C",font=("Arial",24, "bold"))

# Setup a default screen size and Title
wn = Screen()
wn.setup(width = 500, height = 500)
wn.title("RaspPi Temperature Sensor")

# define a static thermo backgroup object and a dynamic bar object
thermo = Turtle()
thermo.penup()
bar = Turtle()
bar.color("red")
bar.hideturtle()

# define an array for the top tube
outline = ((0,-50),(25,-50),(25,210),(-25,210),(-25,-50),(0,-50))
thermo.hideturtle()
thermo.pensize(5)
for pos in outline:
       thermo.goto(pos)
       thermo.pendown()

# add some temperature labels
thermo.penup()
thermo.goto(50,-50)
thermo.write("0 C")
thermo.goto(50,210)
thermo.write("40 C")

# draw the filled bulb at the bottom
thermo.goto(0,-137)
thermo.pendown()
thermo.pensize(5)
thermo.color("black","red")
thermo.begin_fill()
thermo.circle(50)
thermo.end_fill()

# Update the temperature
while True:
       humidity, temperature = Adafruit_DHT.read_retry(11, 4)
       # use a random number for testing
       #temperature = random.randint(0,40)
       drawbar(temperature)
       time.sleep(5)

PI_thermo

Final Comments

Compared to other Python graphic libraries (like PyGame, Tkinter or Qt) Turtle graphics can be slow and perhaps limiting, but for kids Turtles projects are super easy to configure. If you are doing simple stuff Turtles requires a lot less code than the other graphic libraries (keyboard input is a good example of this).

There are a lot of possible fun Raspberry Pi projects that can be done with Turtle. Some of the other projects that we have done include:

  • use a Wii remote to draw pictures
  • create a Turtle drawing as you drive a rover (show the path)