Sunday, December 22, 2013

TEMPer USB Thermometer on Raspberry Pi

TEMPer USB Thermometer
For a fairly cheap solution, nothing quite compares in price and convenience to the TEMPer USB Thermometer.  Due to their low price point, I have used several of these as secondary temperature check points in a server rack before.  They can be picked up for about $15 to $22 on Amazon, or cheaper on eBay.  The TEMPer is not as accurate, or reliable, as something like the Temperature@lert, which runs for about $130, but for general temperature estimation they work sufficient for my needs.

I found the easiest way to use the TEMPer with Python is to install the pyusb library and a simple temper Python class written by Bill Mania.  There were a few small issues that I ran into with the original code, so I forked the code on Github and posted the changes as the PyTEMPer repo seen below.

First let's make sure Linux can see your TEMPer device. We are looking for devices that have the VendorID of 1130 and DeviceID of 660c.
# lsusb | grep 1130:660c
Bus 004 Device 002: ID 1130:660c Tenx Technology, Inc. Foot Pedal/Thermometer

If your device is not found, the PyTEMPer script will not work with your device.

PyTEMPer Installation:
# cd /opt

# ## forked from
# sudo git clone
# cd PyTEMPer

# ## Get PyUSB (if you do not already have installed)
# sudo git clone
# sudo ln -s pyusb/usb usb

# ## Get sample temperature to verify code is setup correctly
# sudo python
0:2, 22.56 Celsius / 72.61 Fahrenheit

Now that we have the PyTEMPer class working, we can build the following Python script to get the current temperature repeatedly:
import sys
import time

import temper
temp = temper.Temper()

if not temp.devices:
    print "Error: not TEMPer devices found!"
device = temp.devices[0]

while True:
    # get temperature
    tempc = temp.getTemperature(device)
    print "Celsius: " + str(tempc)

    # only check temperatures every 10 seconds

In the final lala-pi TEMPer code, I included code to demonize the process, syslog for logging, and ZeroMQ messaging.  If you are interested in the full lala-pi source code (still a work in progress), this can be found in the GitHub lala-pi repo on Bitbucket.
# git clone

More to come...   see label: lala-pi

USB Keyboard on Raspberry Pi

Targus Numeric Keypad

For the lala-pi "room security system" project I am building, I needed a way for an intruder to enter in a security code to disable the security system.  A full keyboard is a bit too bulky.  Luckily, small USB numeric "Ten Key" keypads are common, and fairly cheap.  I am sure their primary market is for accountants, but I purchased one to accompany my small laptop keyboard, some years ago.

Targus keypad model

I connected the keypad to the Raspberry Pi, and immediately noticed the first roadblock.  The keypad sends key presses to the system console, not to the SSH session I use to manage the Pi.  As this Pi will be headless, I needed to find a way to capture input from the keypad.

Fortunately for me, there is already a Python project called "evdev" that:
"provides bindings to the generic input event interface in Linux. The evdev interface serves the purpose of passing events generated in the kernel directly to userspace through character devices that are typically located in /dev/input/"

This solution would work equally well with a keypad or a full-sized keyboard.  The only difficult problem was determining which /dev/input/ device to use.  This particular keypad appeared as "/dev/input/by-id/usb-ORTEK_USB_Keyboard_Hub-event-kbd".  Your's may appear differently.

Here is the first bit of code I used to test the keypad, which worked quite well:
#!/usr/bin/env python

import string
import os
import sys
import time

# pip install evdev
from evdev import InputDevice
from select import select

# look for a /dev/input/by-id/usb...kbd or something similar
DEVICE = "/dev/input/by-id/usb-ORTEK_USB_Keyboard_Hub-event-kbd"

dev = InputDevice(DEVICE)

while True:

    # wait for keypad command
    r, w, x = select([dev], [], [])

    # read keypad        
    for event in
        if event.type==1 and event.value==1:
            if event.code in keys:
                print "KEY CODE: " + event.code
                # do something with this key press
                # ...

In the final lala-pi keypad code, I included code to demonize the process, key-code to key-name mappings, syslog for logging, and ZeroMQ messaging.  If you are interested in the full lala-pi source code (still a work in progress), I setup a GitHub lala-pi repo.
# git clone

For reference, this is the keycode to key name mapping I use:
# keymapping determined by trial and error
keys = {
 79: "1",
 80: "2",
 81: "3",
 75: "4",
 76: "5",
 77: "6",
 71: "7",
 72: "8",
 73: "9",
 82: "0",
 83: ".",
 28: "ENTER",
 78: "+",
 74: "-",
 14: "BS",
 55: "*",
 98: "/",
 # Numlock keys:
 111: "N.",
 110: "N0",
 107: "N1",
 108: "N2",
 109: "N3",
 105: "N4",
 # notice the missing N5
 106: "N6",
 102: "N7",
 103: "N8",
 104: "N9",

More to come...   see label: lala-pi

Saturday, December 21, 2013

ZMQ Messaging System - lala-pi

ZeroMQ Messaging Service
The first hurdle I ran into with this over-engineered room security system, was the complexity of the monolithic application, I was putting together, to control the various sensors and devices.  Luckily, a coworker suggested I break the system up into smaller components and use a messaging system.  This is a common practice for enterprise level applications.

Message-oriented middleware (MOM)

For reference: "Message-oriented middleware (MOM) is software or hardware infrastructure supporting sending and receiving messages between distributed systems. MOM allows application modules to be distributed over heterogeneous platforms and reduces the complexity of developing applications that span multiple operating systems and network protocols. The middleware creates a distributed communications layer that insulates the application developer from the details of the various operating systems and network interfaces." (ref)

That is a fancy way of saying that instead of a monolithic application, smaller self contained applications send messages and requests between each other.  This allows individual components to be maintained individually, and also allows one to potentially duplicate components for distributed load balancing.

Would my little security system become more complex, or simplified by adding a messaging system?  I determined that the education alone would be worth it, so I jumped onto the messaging system bandwagon.

Messaging System Options

I researched several messaging system options, with my primary requirements being:

  • Compatibility with the Raspberry Pi
  • Compatibility with Python
  • Low memory footprint
  • Fast performance
After investigating popular options such as ActiveMQ and RabbitMQ, I settled on a tiny messaging system called ZeroMQ.


ZeroMQ (also ØMQ or ZMQ) is a minimal Message-oriented middleware (MOM).  It is only a small step above just using bare TCP sockets, but provides enough messaging power to do pretty much anything you could want.

The first benefit of ZeroMQ is it takes the TCP socket stream and breaks it down into the individual messages for me.  I then don't have to worry if the partial data stream I receive is complete or not.  With ZeroMQ you receive the whole message, or not.  Messages are all "string" based, which makes them easy for Programming languages like Python to handle.  If you need to send non-string messages, you will need to decode them from the received string, or play with the optional RAW messaging functions.

The second benefit of ZeroMQ is it handles connections for me.  I don't have to worry about if a connection is lost, as it will reconnect for me, when able to.  I also don't have to worry about if a server doesn't exist at the time a client connects, as ZeroMQ will auto connect to the server when the server eventually comes online.

The third benefit of ZeroMQ is it handles distributed messages out of the box.  I can send a single message to my publishing pipe, and any clients that are subscribed to that pipe will receive the message.

ZMQ Patterns

According to the ZeroMQ documentation, the following messaging patterns are baked into it's core:
  • Request-reply, which connects a set of clients to a set of services. This is a remote procedure call and task distribution pattern.
  • Pub-sub, which connects a set of publishers to a set of subscribers. This is a data distribution pattern.
  • Pipeline, which connects nodes in a fan-out/fan-in pattern that can have multiple steps and loops. This is a parallel task distribution and collection pattern.
  • Exclusive pair, which connects two sockets exclusively. This is a pattern for connecting two threads in a process, not to be confused with "normal" pairs of sockets.
The pattern I have chosen to use for my room security system is the Publisher-Subscriber model, with a message router in the middle that will replay all messages to every other application in the system.  Applications can then choose which messages to subscribe to (or even all of them), and which to ignore.

For example, my keypad application will be waiting for a key press.  When a key is pressed, such as the "LEFT" key, it will generate a "KEY: LEFT" message and send it to the message router.  The message router will then turn around and replay the "KEY: LEFT" to any application that is subscribed to messages prefixed with "KEY:".  The music player application, which is listening for "KEY:" will then pick up the message and take the predetermined action, such as going to the previous song.

Another fascinating side effect from this setup is I could generate a "KEY: LEFT" message from any application, such as a web interface, or even a cell phone app.  Security issues aside, think of the possibilities.  I know, this blew my mind too!


There are two parts to get ZeroMQ installed and working with Python.  First, you need the system libraries, and second the Python bindings.

System Libraries:
# For Raspbian:
apt-get install python-zmq

Python Binding:
easy_install pyzmq
# or
pip install pyzmq

Source Code

If you are interested in the full code (still a work in progress), see the lala-pi repo on GitHub.
# git clone

Message Router

As ZeroMQ is a minimal messaging system, you are left on your own to build the messaging router services.  Thankfully this is quite simple.

Here is the minimal message router I started with:
#!/usr/bin/env python

import os
import sys
import time

import zmq

# ZMQ context, only need one per application
context = zmq.Context()

# for sending messages
z_send = context.socket(zmq.PUB)

# for receiving messages
z_recv = context.socket(zmq.SUB)
z_recv.setsockopt(zmq.SUBSCRIBE, '')  # subscribe to everything

print "ZMQ server started."
while True:
    message = None

    # wait for incoming message
        message = z_recv.recv()
    except zmq.ZMQError as err:
        print "Receive error: " + str(err)

    # replay message to all subscribers
    if message:
        except zmq.ZMQError as err:
            print "Send error: " + str(err)

I then added some logging of the messages, and a bit of clean up code for a more robust message router:
#!/usr/bin/env python

import os
import sys
import time

import zmq

# ZMQ context, only need one per application
context = zmq.Context()

# for sending messages
z_send = context.socket(zmq.PUB)

# for receiving messages
z_recv = context.socket(zmq.SUB)
z_recv.setsockopt(zmq.SUBSCRIBE, '')  # subscribe to everything

# record all message requests to a file
record = open('router-records.txt', 'w')

# counters for messages
last_time = time.time()
count = 0

print "ZMQ server started."
while True:
    message = None

    # wait for incoming message
        message = z_recv.recv()
    except zmq.ZMQError as err:
        print "Receive error: " + str(err)

    # if message received, and not an error, then
    # replay message to subscribers
    if message:
        count += 1
        record.write(str(count) + ':' + message + '\n')
        # occasionally flush the router-record.txt file
        if time.time() > last_time + 2:
            last_time = time.time()

        except zmq.ZMQError as err:
            print "Send error: " + str(err)

        if message.strip() == "DEATH":
            print "Death received, shutting down."

print "Shutting down..."
print "Shut down."

My final version also includes some "forking" code to daemonize (background) the application. As print statements would be lost to the void, I also converted all of the print statements over to using syslog.  The full source can be found in the Bitbucket repo.

Now, with a working router, I can build any application, connect to the message router and have a fully functional messaging system.

Message Client

For a sample messaging client, here is my "test" client that I use. Using this as a template, a full application could be constructed
#!/usr/bin/env python

import os
import sys
import time

import zmq

context = zmq.Context()

z_recv = context.socket(zmq.SUB)

z_send = context.socket(zmq.PUB)
# z_recv.setsockopt(zmq.SUBSCRIBE, 'KEYBOARD:')
z_recv.setsockopt(zmq.SUBSCRIBE, '')  # subscribe to everything

print "ZMQ Client Started!"

while True:
    sys.stdout.write("Message: ")
    message = raw_input().strip()

    if message:
            print 'SEND:' + message
        except zmq.ZMQError as err:
            print 'Send error: ' + str(err)

        # don't block if no message waiting
        in_message = z_recv.recv(zmq.DONTWAIT)
        print 'RECV:' + in_message
    except zmq.ZMQError as err:
        print 'Receive error: ' + str(err)

More to come...   see label: lala-pi

Room Security System - lala-pi

Concept design of room security system

My daughter asked if I could build a security system for her room.  Her brother tends to sneak in and play with her makeup and stuff.  I thought about it for a few minutes, and my mind started racing with fantastic ideas.  Challenge accepted!  And just like an engineer, I way over engineered this project.  I am calling this project lala-pi in honor of my daughter's nickname.

Of course the whole thing is being built around a Raspberry Pi.  I already have several of the components up and working.

The way this security system will work is when an intruder enters the door, it will trigger the magnetic reed sensors attached to the door.  This in turn will trigger a GPIO pin on the Raspberry Pi.  The Raspberry Pi will respond by taking a picture through the web camera, and generate an audible warning through the speakers.  The Pi will then give the intruder a few seconds to approach the attached USB keypad, enter in the security code and disable the security alarm.

If they fail to enter in the security code, the system will then trigger a full scale assault, including sirens through the speakers, additional photos for evidence, and a notification sent to cell phones.  (Do you thinking electric shock panels embedded into the floor are a good idea, or have I been playing too much Tomb Raider?)

But why stop there?  With wireless access, a keypad, speakers and Pandora, I am going to also turn this into a internet music player.  And with access to Google Calenders, I am going to include an optional musical alarm clock feature.  Just for good measure, I am throwing in a temperature sensor, motion detector and extra USB storage.  If I get really ambitious, I would like to include some power control switches and have the lights go/off based on motion detection.

I know what you are thinking, I should round things off by embedding a large red circle light on the wall, and calling it Hal.
Hal 9000 - "I'm sorry Dave, I'm afraid I can't do that"

If you are interested in the final full code (still a work in progress), I setup a project (lala-pi repo) on GitHub.
# git clone

More to come...   see label: lala-pi

Sunday, December 15, 2013

Raspberry Pi with Arduino Slave

The power of the Raspberry Pi is incredible, but amazingly there are tasks which it is not fully equipped to handle.  Such items are 5V Logic (for certain chip sets and controllers), Analog I/O (for variable level sensors) and Real Time operations (for motor controllers).

Arduino Uno

A common solution is to attach another micro-controller board such an Arduino.  The Arduino is a versatile micro-controller that comes in a variety of sizes and packages with "Shields" for advanced expansion.  The most common version is the Arduino Uno (pictured below).

Arduino Uno Packaging
Arduino Uno fits in the palm of your hand
There are several methods to communicate with an Arduino from the Raspberry Pi. Serial, I2C and GPIO are common methods.  The method I prefer is to communicate over Serial, through the USB port, that I program and power the Arduino with (not to be confused with Serial through the serial pins on both boards).

To connect the Arduino Uno, using a USB cable (USB type B to A cable) I connected it to a powered USB hub.  Then I connected the USB hub to my Raspberry Pi.  If your power adapter is sufficient amperage, you should be able to connect the Arduino directly to the Raspberry Pi.  I will have several other USB device attached, so the USB powered hub works best for me.

Arduino Uno connected to USB
connected to Raspberry Pi
Arduino Uno close up

Arduino IDE

Now that the Arduino is attached to the Raspberry Pi, we can program the Arduino using the Arduino IDE.  This can be installed as easy as:
# sudo apt-get install arduino

And then running the Arduino IDE, from within a Windows Manager, with:
# arduino

Arduino Getting Started (Blink)

The Arduino Getting Started Guide has excellent instructions for getting started with the Arduino.

As the Arduino Uno is the "default" for the Arduino IDE, we do not need to make any changes to the IDE to be able to upload our program (Arduino calls the programs Sketches) to Arduino.

From the template Sketches, select the "Blink" example.  This sketch will cause the little LED (labeled "L" on my Arduino Uno) to blink on and off.
For now, go ahead and click the "Build/Verify" button to compile this sketch into Arduino binary code.  Finally click the "Upload" button to send the code to the Arduino.  A few seconds later the Arduino should blink on and off.

Congratulations, you can now program the Arduino from your Raspberry Pi.

What's Next?

Next, I will cover how to program the Arduino from the Command Line, and how to talk to the Arduino through Serial (over the USB port)

Saturday, November 30, 2013

PiMAME - Retro Gaming on the Raspberry Pi

There have recently been a number of cool projects where the Raspberry Pi has been used to build a retro arcade cabinet. There is quite a bit of effort in fabricating a full arcade cabinet, but one can still enjoy the old arcade games just by connecting the Raspberry Pi to a TV and installing some software. One fairly complete software solution is PiMAME, which is a modified Raspbian built with all of the common emulators preinstalled. If you have ever attempted to compile just MAME on a Raspberry Pi, you can appreciate not having to burn those 6+ hours.

PiMAME - "PiMAME is the gaming OS for the Raspberry Pi. PiMAME runs MAME, Neo Geo, and PlayStation games out of the box, and is constantly being updated with new emulators and tools. Included is a suite of software designed to reduce the complexity and time needed to setup a fully working system. An updater is included with the distribution. PiMAME is based off of Raspbian, the official Linux distribution for the Raspberry Pi."


PiMAME includes the following Arcade Emulators:
  • AdvanceMAME
  • Neo Geo (GNGeo)
  • MAME4All
  • FBA (CPS1, CPS2, Neo Geo)

PiMAME also includes the following Console Emulators:
  • PlayStation 1 (PCSX_ReARMed)
  • Genesis (DGen)
  • Nintendo Emulators
    • SNES (PiSNES / SNES9x Advmenu)
    • NES (AdvanceMESS)
    • Gameboy (Gearboy Advmenu)
    • Gameboy Advance (gpsp)
  • Atari 2600 (Stella)
  • Commodore 64 (VICE)


To enjoy PiMAME, one only needs to download the compressed image (1.6 GB), extract the image (4 GB), write the image to an SD card and power on the Pi (quickstart). I would highly recommend burning this image onto a secondary SD card, so as not to destroy your hard work on your current Pi setup. You really should have a couple of free SD cards laying around when playing with a Raspberry Pi.

Download and write the image to a SD card:
# wget
# unzip
# sudo dd if=pimame-0.7.10.img of=/dev/sdh bs=1M

It took about 10-20 minutes to write the 4 GB image to my SD card. The /dev/sdh is where my USB SD Card Reader appared on my system. Check dmesg after connecting your USB SD Card Reader to determine the correct device node for your system.

Once the system boots, make sure to manually run raspi-config and use the common options such as "Expand Filesystem", "Change User Password", "Hostname", etc. The raspi-config tool is not auto run on boot like it is with the base Raspbian distribution.


As you power on the Raspberry Pi if you see the PiMAME logo (pictured above) you know you burned the right image. Once the PiMAME has fully booted, you will be presented with the following menu:

From this menu you can start the various game emulators.  You can also start some maintenance operations (under Tools) such as raspi-config, reboot and shutdown.  Unfortunately, the system update is not included in this menu.

If you happen to exit the PiMAME Menu, you can return to it by running:
# python /home/pi/pimame_files/

Add ROMs Through Web Interface

The PiMAME comes with a convenient built in web server that can be used to add ROMS. There is also a built in FTP server (recommended for files over 50 MB), for whichever is more convenient.

NOTE: All ROMs should be stored in the /home/pi/roms/ directory

To determine your IP address, you simply select "Tools" from the menu. Your IP address will be listed at the top of the "Tools" page.

Once you have the IP address, open up a browser and browse to the IP address.

Click the "ROM Uploader" button, and login. Select the "roms" folder. This is where your ROMs should go.


PiMAME only comes with one freeware ROM by the name of 'Gridlee'.

So where does one get other game ROMs from?

Less Legal: ("Yo Ho, Yo Ho, A Pirate's Life For Me")
Just in case you are curious, there is a very small handful of game creators that have opted to allow legal usage of their game ROMs.  Unfortunately, none of these are any of the big game developers like Nintendo, who are very actively against emulators and ROMs.


Let's see one of the emulators in action.  As Gridlee is the only included ROM, let's play Gridlee.  To start Gridlee, from the PiMAME menu, select "Arcade Emulators" then "AdvanceMAME".  When AdvanceMAME loads there will be only one game listed, Gridlee.  Press enter to start Gridlee.

The point of Gridlee is to move your character around and catch the bouncing balls.  There are also tall cylindrical enemies you can shoot, before they electrify the ground and hurt you.

I was a bit frustrated at first, trying to determine what they key bindings were and how to start the game.  To save you a few seconds, press "1" to start a single player game, or press "2" for a one-at-a-time two player game.  Press "5" to add coins for player 1 and press "6" to add coins for player 2.  The arrow keys will move your character around, and the "Control" key will fire your weapon.  You can press "F1" to see a list of the key options.


To perform updates and other tasks, I prefer to do these from a remote SSH session. As mentioned before, to determine your IP address, you can simply select "Tools" from the menu, or you can exit the PiMAME Menu and run ifconfig. Your IP address will be listed at the top of the "Tools" page.

The default user login is user "pi" with a password of "raspberry". When you connect through SSH the PiMAME menu will appear. This is due to PiMAME being set to start in the user's profile. None of the applications will run from a SSH session, so select menu option "6 - Exit" to return to the console.

Once you are in the shell, you can run the PiMAME update (or other console tasks).
# cd pimame_installer/
# sudo ./

# sudo reboot

Friday, November 29, 2013

Raspbian Wireless Wi-Fi

Are you wanting to connect to your Raspberry Pi over WiFi?  The following are instructions for configuring WiFi on Raspbian (the other Debian based Raspberry Pi distributions should work in a similar manner).

Although the Raspberry Pi model B conveniently comes with an Ethernet port (the model A does not), there are a number of applications where having WiFi is super convenient.  I have one of my Raspberry Pi out in our garage, controlling and monitoring the garage door.  Running a network cable would have been a very ugly solution.

To connect via wireless one must add a WiFi USB dongle, which will consume one of your precious few available USB ports (maybe time to expand with a powered USB hub).  There are other low level hardware options, but nothing quite as simple, and plug and play, as a WiFi USB dongle.

There are a number of compatible WiFi USB dongles on the market.  Review the RPi USB Wi-Fi Adapters list for verified adapters.  My personal favorite is the Edimax EW-7811Un 150 Mbps Wireless 11n Nano Size USB Adapter (pictured above), as it is popular, works fairly well, and is only $9 on Amazon (with Amazon Prime).

To enable WiFi, simple connect your WiFI USB dongle to an available USB port, modify your network interfaces configuration file and restart your Pi.  To configure the network interfaces configuration file, add the wlan0 section to /etc/network/interfaces:
auto lo
iface lo inet loopback

iface eth0 inet dhcp

auto wlan0
allow-hotplug wlan0
iface wlan0 inet dhcp
        wpa-ssid "YOUR_SSID"
        wpa-psk "YOUR_WEP_OR_WPA_KEY"
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

iface default inet dhcp

Your WPA key above can specified as either be the clear text passphrase, or the hex encoded version.  If you would prefer to not list your clear text passphrase you can generate the encoded hex version with the wpa_passphrase tool or even online tools.
# wpa_passphrase test testtesttest

WPA passwords are managed on Linux with the wpa_supplicant tools.  The wpa_passphrase tool is designed to generate a section that can be added to the /etc/wpa_supplicant/wpa_supplicant.conf configuration file.  You can also add multiple SSIDs to wpa_supplicant.conf.  If you have multiple SSID you may want to connect to (such as a mobile Raspberry Pi), don't add the wpa-ssid and wpa-psk lines to the interfaces file.  Instead use the wpa_passphrase tool to add multiple sections to the wpa_supplicant.conf configuration file.

You can auto add the output of wpa_passphrase, to the wpa_supplicant.conf, with the following:
# wpa_passphrase test testtesttest >> /etc/wpa_supplicant/wpa_supplicant.conf

Finally, to bring up the wireless, either reboot the Raspberry Pi, or run the following:
# ifdown wlan0
# ifup wlan0

You should now be able to use your Raspberry Pi over WiFi.

For reference, there are several command line tools that can be used to manually configure and view wireless settings.

To see your wireless IP address:
# ifconfig wlan0
lan0     Link encap:Ethernet  HWaddr 80:1f:02:be:XX:Xx
          inet addr:  Bcast:  Mask:

To manually configure SSID and other wireless options, the iwconfig command can be used. The output of iwconfig looks similar to the ifwconfig, but with wireless settings:
# iwconfig wlan0
wlan0     IEEE 802.11bg  ESSID:"MY_SSID"  Nickname:""
          Mode:Managed  Frequency:2.437 GHz  Access Point: 00:14:BF:E0:XX:XX
          Bit Rate:54 Mb/s   Sensitivity:0/0
          Encryption key:****-****-****-****-****-****-****-****   Security mode:open

To scan for wireless access points:
# iwlist wlan0 scan
wlan0     Scan completed :
          Cell 01 - Address: 00:14:BF:E0:89:XX
                    Protocol:IEEE 802.11bg
                    Frequency:2.437 GHz (Channel 6)
                    Encryption key:on
                    Bit Rates:54 Mb/s

Wednesday, November 27, 2013

Raspbian Installation

The Raspberry Pi is a great little device that can be used for hardware hacking, environment monitoring, electrical engineering, media center and anything else one can imagine.  But, the Raspberry Pi does not come with an Operating System.  So first things first, we need to install one.  The absolute most popular distribution is Raspbian, based on Debian Wheezy.

Write Image

Raspbian comes as a disk image, which needs to be downloaded and written to a SD card.  The SD card needs to be at least 4 GB and at least a class 4 (speed).  The SD card will then be inserted into the Raspberry Pi and finally powered on.  I will be using Linux to write the disk image to the SD card.  If you are using Windows, you can use the "Win32DiskImager" tool (See Connecting to the Pi).

The following will download Raspbian and write it to the SD card.  At the time of this writing, the latest version of Raspian is  Adjust the file name if latest has changed.  The disk image is about 600 MB so be patient as it downloads.  Writing a 600 MB image to an SD card is also slow (about 7 minutes), so additional patience will be needed here as well.

# wget
# unzip
# sudo dd if=2013-09-25-wheezy-raspbian.img of=/dev/sdh bs=1M

The /dev/sdh is the device node my USB SD card reader/writer appeared as.  I used dmesg, after connecting the USB device, to determine this.

Now that we have the image written to the SD card, we can plug it into the Raspberry Pi and power it on.  To make life easier one should connect an HDMI (or RCA video) to both the Raspberry Pi and a TV, connect a USB keyboard and mouse (optional), connect network via Ethernet (optional), connect finally connect power through a USB Micro cable.  The Raspberry Pi will now begin to boot, and you should see the boot process, with a little raspberry image logo, on your TV.


On the first boot, you will be presented with the text dialog based raspi-config tool.

This tool can be used to configure a variety of features, but for now it is important to just "Expand Filesystem".  This will take our 600 MB image and expand it out to the full size of our SD card, which can vary in size.

The other 3 options I like to change at this point are User Password, Boot to Desktop, Time Zone (found under Internationalization Options), Hostname (under Advanced Options), and Memory Split.

If you would like to announce to the world your usage of the Raspberry Pi, select the Add to Rastrack option, which will add this Pi to the online Raspberry Pi Map.  Others can then see your Pi on the Rastrack map.

If you need to modify these configurations at a later time, the raspi-config tool can be rerun with:

# sudo raspi-config

The raspi-config tool can also be run over SSH, if that is more convenient.

Once you are happy with your changes, quit out of raspi-config.  It will ask if you would like to reboot, if needed, and you should.

Desktop vs Headless

There are two modes the Raspberry Pi is commonly run in: desktop and headless.  Raspbian defaults to booting to headless mode.

With desktop, one is interested in interacting with the Pi through a GUI with mouse and keyboard.  Within raspi-config, you will want to set the "Boot to Desktop" option and also modify the "Memory Split" to the 64 MB default, or higher.  The "Memory Split" determines how much memory is allocated to the GPU.

With headless, (Raspian's default) one is interested in interacting remotely with the Pi through SSH or a web interface.  You will want to set the "Boot to Console" option and drop the "Memory Split" to a minimal 16 MB.

Default Login

Raspbian is setup with a default user by the name of "pi".  The default password for user pi is "raspberry", unless this was changed within raspi-config.


The Raspberry Pi is far more useful with network access.  Simply connect an Ethernet cable to Raspberry Pi and it should acquire an IP address on boot.  To determine your IP address, run the "ifconfig" command.

# sudo ifconfig
eth0      Link encap:Ethernet  HWaddr b8:27:eb:28:ea:55
          inet addr:  Bcast:  Mask:

With the IP address, you can now connect to the Raspberry Pi over SSH, which opens a world of possibilities.

Wireless access is also possible, but you will need to purchase a WiFi dongle and modify some configuration files.

System Update

Lastly, there are constantly changes being made to the packages installed.  Raspbian (Debian based) uses APT for package management.  To keep your system updated, you should occasionally run the following commands:

# sudo apt-get update
# sudo apt-get upgrade
# sudo apt-get dist-upgrade  # (optional)

APT Package Management

A quick overview of APT package management... (I use the package "screen", a terminal multiplexer, in this example

To install a package: (apt-get install [package])

# apt-get install screen

To uninstall a package: (apt-get remove [package])

# apt-get remove screen

To search for a package: (apt-cache search [package])

# apt-cache search screen

To see package informaiton: (apt-cache show [package])

# apt-cache show screen

RaspBMC Media Center Installation

The Raspberry Pi can be used as a media center.  The Raspberry Pi media center can serve up media such as music, videos and pictures.  There are a number of distribution options based on XBMC the "Open Source Home Theatre Software".  The two most popular are RaspBMC and OpenELEC.  The following is a quick guide for installing RaspBMC.

Write Image

First, download latest RaspBMC image and write to SD card:
# wget
# gzip -d raspbmc-2013-10-02.img.gz
# sudo dd if=raspbmc-2013-10-02.img of=/dev/sdh bs=1M

I used Linux to write the image to the SD card.  If you are using windows, you can use the "Win32DiskImager" tool (See Connecting to the Pi).  The raspbmc-2013-10-02.img.gz was the available version at the time of this post, adjust the file name as needed.  The /dev/sdh is the device node my USB SD card reader appeared as.  I used dmesg, after connecting the USB device, to determine this.

First Boot

Connect an HDMI cable to both the Raspberry Pi and a TV.  If you are planning to serve media files up from another server (across NFS / CIFS), connect a network cable.  Although it is possible to use wireless, it is recommended to use at least a Fast Ethernet wired cable, otherwise the video performance may suffer.  Connect power, and watch the Raspberry Pi boot.

On the first boot, you will be asked to configure a few of options, such as locale and time, within a text based dialog wizard.  The configuration options are minimal compared to Raspbian's raspi-config.  The Raspberry Pi will reboot again, this time into RaspBMC windows manager (pictured above).

You are now ready to start using the RaspBMC Media Center.

Serving Media from USB

The quickest way to play media is to copy the media files to a USB drive, and connect this to the Raspberry PI.  From here, it is just a matter of browsing to the files you wish to play.

Service Network Media over NFS

If you are like me, you have a massive file server in the basement housing your collection of music, videos and photos.  To remotely gain access to these files, we can mount an NFS (or CIFS) share.

The NFS tools are already available, but to mount an NFS share we need to first enable the RPC Binding service.
sudo service rpcbind restart
sudo update-rc.d rpcbind defaults

Next we can  mount our NFS share:
sudo mkdir /pub
sudo mount myserver:/pub /pub

Adjust "myserver" and "/pub" to match your server name and NFS share.

To make this available on boot, add the following to /etc/fstab:
myserver:/pub      /pub            nfs     defaults        0 0

Now you will have full access to your media from your Raspberry Pi.

DVD Playback

The Raspberry Pi can also playback MPEG encoded videos, but first you will need to purchase a MPEG-2 license from for about $4.  After waiting about 72 hours for your license key to arrive by email you can then add your license key to /boot/config.txt.  Now you will be able to play your MPEG encoded videos through RaspBMC.

Sunday, October 6, 2013

Garage Door Part 2 - Monitor Door (GPIO Input)

Project Garage Door
Now that I can trigger our garage door, I needed a way to determine if the garage door is open or closed.  I purchased a Magnetic Reed Switch (commonly used for windows Theft Deterrence) to detect this change.
Magnetic Reed Switch
The way a reed switch works is as the magnetic block nears the switch block, the sensitive switch is pulled closed, and the circuit will be completed.

This particular magnetic switch is really nice, as it includes terminals for both Normally Closed (NC) and Normally Opened (NO), depending on your needs.  Most cheaper reed switches only include a Normally Opened option.  For my setup I choose to use the Normally Opened (NO), so the triggered switch would close the circuit loop.  Either configuration could be used, and would just need to be adjusted in the code logic.  This magnetic switch also includes the option of being taped (included) or screwed/nailed to a surface.

I ran a couple of tests with the switch and Raspberry Pi, to make sure the switch would work as expected, and the code would detect the changes.  Once I was satisfied with the results, it was time to mount the components to their final resting places.

I tried finding a position on the wall that I could mount the magnetic switch, but no position appeared to get close enough to the door, but yet far enough away to not get stuck.  I finally settled on attaching the switch block to the garage floor and the magnetic block to the bottom of the garage door, within the groove.  I found that the door does not actually touch the ground as there is weather stripping in the way, which gave excellent clearance for the switch.

Magnetic switch - switch block
Magnetic switch - magnetic block

Then I ran a pair of 20 gauge "bell" wires from the magnetic switch, up the wall, across the ceiling and down to my Raspberry Pi.  I left a bit of slack on each end, just in case I need to make adjustments in the future.  To keep the wires from falling, I used a simple stapler, as the wires were very light weight.  The Raspberry Pi, breadboard, and USB Hub are all bundled within the plastic blue box, to keep the dust (and cat) away.
Wires running to Raspberry Pi

Wires running along the ceiling

To finish the circuit I then needed to connect the switch to power, ground and GPIO pins.  The following schematic is the recommended circuits for a simple switch input circuit, and includes Pull Up and Pull Down resistor configurations.  The most commonly used layout is the Pull Up resistor so this is what I will use for my circuit (either could be used).  (Please read Pull-up Resistor for more information, if curious)
GPIO Input Circuits with both Pull Up (top) and Pull Down (bottom) configurations
My "Pull Up" input circuit that matches the above schematic

The whole bundled mess, found within the protective plastic box:

Raspberry Pi, breadboard and USB Hub within protective plastic box
I use the following Python code, running on the Raspberry Pi to test and report if the switch is opened or closed.  This code is the foundation for a much larger bit of code used for monitoring, opening and closing the garage door.
#!/usr/bin/env python

import sys
import time

import RPi.GPIO as GPIO

pin = 25

GPIO.setup(pin, GPIO.IN)

  while True:
    input_value = GPIO.input(pin)
    if input_value:

Next, we will look at a simple web interface to control the garage door: Garage Door Part 3 - Web Interface

Pull-up Resistor

What is a Pull-up Resistor?

Imagine the following simple circuit:

Simple "floating" switch circuit
When the switch is closed there is a complete circuit from GPIO pin to ground.  A reading of the GPIO pin will read "low".

What happens when the switch is opened, though?  This leaves the GPIO pin in a "floating" state which is unable to determine a "high" or "low" state.  If you now read the GPIO pin, it will randomly report high and low states.

To force the GPIO pin to a "high" state, when the switch is open, we can add a very high Ohm resistor to the circuit and to the voltage source.
Simple switch circuit with Pull Up resistor

As the resistor is so high, when the switch is closed the resistor does not directly affect the rest of the circuit.  But when the switch is opened, the high resistance is better than no path and will "Pull Up" the circuit path to the voltage source, so the GPIO pin will now detect a "high" state.

Depending on if you want the opened switch circuit to be pulled up to the voltage source, or pulled down to the ground, different circuits can be built:
Input Circuits with "Pull Up" (top) and "Pull Down" (bottom) configurations

"Pull-up resistors are used in electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected or high-impedance is introduced. When the switch is open the voltage of the gate input is pulled up to the level of Vin. When the switch is closed, the input voltage at the gate goes to ground.  A pull-up resistor weakly "pulls" the voltage of the wire it is connected to towards its voltage source level when the other components on the line are inactive. A pull-down resistor works in the same way but is connected to ground." (source)

Sunday, September 29, 2013

Garage Door Part 1 - Open Door (GPIO Output)

Project Garage Door

My vision for our Garage Door is to have an automated way to open and close it from both a web interface and a proximity sensor.

It has taken me a couple of weeks to finally get everything working, but I finally have my garage door automated, with the help of the Raspberry Pi.  I will break out each of the steps it took into a different article: Open Door (GPIO Output), Monitor Door (GPIO Input), Web Interface, Vocal Notification, Proximity Sensor.

First step was to get the garage door to open.  I started with trying to determine how I could get the Raspberry Pi to trigger the garage door to open/close.  After inspecting the wired garage door button, I found a simple solution to trigger the garage door.
Garage door button
The garage door button has two wires that run all the way to the garage door motor.  I found that by simply jumping the two terminals (circled in red below) this would trigger the garage door.  (FYI: The right two terminals are used for the safety closing door sensor, which makes the center terminal a common terminal).  This made the solution fairly easily, as I would simply need to electronic switch to close the circuit, which I had already posted a working solution for in my Driving a Relay using GPIO and Automated Sprinkler System First Look (Relay Module) articles.
Garage door motor
I could have run wires all the way from the Raspberry Pi to the garage door motor, but as the garage door button was much closer, I instead ran a set of wires (20 gauge door bell wire I picked up from Home Depot for cheap) to the back of the garage door button and connected them to the screw terminals I found there (Note: these new wires can be seen as the red/white combo in the garage door button picture above).

I then connected the Raspberry Pi, with attached Wifi dongle, to a breadboard and wired up a relay (relay-diode-transistor-resistor) as described in Driving a Relay using GPIO).  A pre-built Relay Module would have been easier, but I did not have an extra one on hand at the moment.  I then placed the Raspberry Pi and breadboard into a plastic container, to keep the dust off (which I cut holes for venting).

Raspberry Pi in plastic container to protect from dust

To trigger the electronic relay switch, which will in turn close the garage door button loop, I use the following Python code.
#!/usr/bin/env python

import RPi.GPIO as GPIO
import time



    print "Trigger Garage Door"
    print "Cleaning up..."

You may have noticed that the code makes no mention of if it will be opening or closing the door.  That is because at this point, there is no way for the code to determine the current state of the garage door.

Stay tuned, in the next article, for solution to detect the state of the garage door: Garage Door Part 2 - Monitor Door (GPIO Input)

Saturday, September 14, 2013

Monitoring a UPS

The original reason for my interest in the Raspberry Pi was for a mini computer to monitor a UPS and alert us if there was a power loss.  The following is how I setup the Raspberry Pi to monitor the UPS and send an email to our cell phones in the event of a localized power loss.
CyberPower LCD "Smart" UPS

Short Story of Education the Hard Way

(note to reader: If you are just interested just in the UPS monitoring details, skip ahead...)

What are we monitoring with the UPS?  Well, we have a small chest style deep freezer in our garage.  We store steaks and other expensive meats in it.  Anytime there is an excellent sale, my wife stocks up on meats.  A few months ago, something caused the GFCI to trip, and we didn't notice until a few days latter when the rancid smell reached us.  We estimated over $500 worth of meat lost in one fell swoop.  So the wife tasked me with coming up with a solution to avoid a repeat in the future.

So my solution was to use a "smart" UPS, one that I could actively read the metrics from, and send a email notification in the event of a power failure.  The second benefit, or so I had thought, is the UPS could keep the fridge powered for short term power loss.  I already have a CyberPower UPS connected to my file server, and it works great for battery backed power outages, monitoring battery reserves, and shutting down the server if the reserves deplete.

A bit of painful education.  I wanted to make sure I purchased the "right" size of UPS, so I pulled out my Kill A Watt power meter and connected it to the refrigerator.  During the occasional freeze cycle it appeared to pull about 460-490 Watts, and lasted less than a minute.  At idle, it rated closer to 10 Watts.  I rationalized that the UPS should be able to handle a few of these cycles before failing out.

When I looked online for consumer UPS, a majority measured in VA.  So how does one get VA from Watts?  Well, I cheated.  The Kill A Watt also has a VA meter, so I selected that, and it showed around 560-580 VA.  I then found a 600 VA CyberPower UPS.  I admit that I realized 580 to 600 is not a lot of wiggle room, but the next battery size up jumped quite a bit in price.  I crossed my fingers and ordered it.  I should have done a bit more research.

The UPS arrived and I connected it to the freezer.  The freezer's motor kicked on and the UPS went offline.  Clearly I was wrong.

When I actually searched for VA to Watt conversion calculations online, I found that a good estimate is closer to 50% - 60%.  I would have needed almost 800 VA to be on the safe side.  Even this may not have been sufficient, as I learned that the initial motor spike can be quite high.

Lesson learned: You would probably need an industrial sized UPS to battery back a simple freezer.

Well, the battery protection was a bust, but at least I could still use the UPS to monitor for a power failure.  Unfortunately, had I known this, I could have saved a few bucks, and just purchased the cheaper smaller "smart" UPS.  The Raspberry Pi could run for days off even the smallest one.

So onto the technical stuff...

How to monitor a UPS with a Raspberry Pi

The setup.  The Raspberry Pi lives out in the garage, on top of the deep freezer.  I have a USB powered hub connected to the UPS, in one of the battery backed up slots.  The USB hub then powers the Raspberry Pi (to avoid having to waste two power adapters).  To talk to the USB hub I have a second USB cable connected to the data side of the Pi.  To connect to the network, I have a WiFi dongle connected to the USB powered hub.  To try and keep it as clean as possible, I have Raspberry Pi inside a plastic container, with holes for air flow.  Finally, to get as much use of the Raspberry Pi, it also serves double duty and controls/monitors the garage door.

There are numerous "UPS" monitoring packages available, but the one I have had the most success with, is the one from APC called "apcupsd - APC UPS Power Management (daemon)".  Although it was designed for APC branded UPS, it works quite well with numerous other UPS.

I tend to purchase the CyperPower UPS line with the LCD display.  I am a sucker for the LCD that provides quick visual metrics, of the UPS.  The CyperPower UPS connects to a PC through USB and works well with the apcupsd daemon.

Luckily the package is already included in the Raspbian repositories, so installation is this simple:

# apcupsd installation
apt-get update
apt-get install apcupsd

The next step is to modify the configuration scripts, so apcupsd can find the UPS.  Use your editor and modify /etc/apcupsd/apcupsd.conf with the following changes.

# vim /etc/apcupsd/apcupsd.conf


#UPSTYPE apcsmart

#DEVICE /dev/ttyS0

These changes tell apcupsd that the UPS is connected via USB.

Next we want to test our connection to the UPS.  This can be achieved with the 'acptest' program.

# apctest

2013-09-14 14:49:10 apctest 3.14.10 (13 September 2011) debian
Checking configuration ...
Attached to driver: usb
sharenet.type = Network & ShareUPS Disabled
cable.type = USB Cable
mode.type = USB UPS Driver
Setting up the port ...
Doing prep_device() ...

You are using a USB cable type, so I'm entering USB test mode
Hello, this is the apcupsd Cable Test program.
This part of apctest is for testing USB UPSes.

Getting UPS capabilities...SUCCESS

If you see the "SUCCESS", everything is great.  There isn't much here that you will want to change, so let's quit this program and start the apcupsd daemon.

First, enable the service:

# vim /etc/default/apcupsd


Next, restart the service:

# service apcupsd restart

Starting UPS power management: apcupsd.

To have apcupsd auto start at boot:

# update-rc.d apcupsd defaults

Next, we can query the UPS to see the various metrics available to us using the 'apcaccess' application.  The properties that apcupsd supports is quite large, and each UPS uses different properties, so your results may vary.

# apcaccess

APC      : 001,032,0781
DATE     : 2013-09-14 14:54:31 -0600
HOSTNAME : pi-ups
VERSION  : 3.14.10 (13 September 2011) debian
UPSNAME  : pi-ups
CABLE    : USB Cable
UPSMODE  : Stand Alone
STARTTIME: 2013-09-14 14:54:30 -0600
MODEL    : UPS CP600
LINEV    : 120.0 Volts
LOADPCT  :   0.0 Percent Load Capacity
BCHARGE  : 100.0 Percent
TIMELEFT :  82.0 Minutes
MBATTCHG : 5 Percent
MINTIMEL : 3 Minutes
MAXTIME  : 0 Seconds
OUTPUTV  : 120.0 Volts
DWAKE    : 000 Seconds
LOTRANS  : 100.0 Volts
HITRANS  : 140.0 Volts
ALARMDEL : 30 seconds
TONBATT  : 0 seconds
CUMONBATT: 0 seconds
STATFLAG : 0x07000008 Status Flag
SERIALNO : AEC7101.251
NOMINV   : 120 Volts
NOMPOWER : 340 Watts
END APC  : 2013-09-14 14:55:02 -0600

Now that we can query the UPS, let's work with the apcupsd "event" scripts.  This is how we will get an email sent when a power failure occurs.  The event scripts can all be found in the /etc/apcupsd/ folder.  All events are controlled by the /etc/apcupsd/apccontrol master script, so take a quick peak there if you want to know what else can be modified.

The two scripts we are interested in are the "onbattery" and "offbattery" scripts.  The "onbattery" is triggered during a power failure, and "offbattery" is triggered when power returns.

By default these scripts are just simple bash scripts that send a message to the PC's console and send a local email.  Instead of using local mail, we will use Gmail to send our notification, and write the script in Python.  One other side benefit of having these scripts written in Python, is I can also integrate Xively and then update Xively with the various data points of my UPS.

Let's backup the current scripts, before modifying them:
cp /etc/apcupsd/onbattery /etc/apcupsd/onbattery.original
cp /etc/apcupsd/offbattery /etc/apcupsd/offbattery.original

This is the powery failure script I use:

#!/usr/bin/env python

import smtplib
import email.mime.text
import syslog

def log(msg):


from_email = GMAIL_ADDRESS
to_emails = [""]  # cell phone address

msg_subject = "ALERT: UPS Power Failure"
msg_text = "Auto Notification"


msg = email.mime.text.MIMEText(msg_text)
msg['Subject'] = msg_subject
msg['From'] = from_email
msg['To'] = ", ".join(to_emails)
s = smtplib.SMTP_SSL('', '465')
s.sendmail(from_email, to_emails, msg.as_string())

And for when power returns:

#!/usr/bin/env python

import smtplib
import email.mime.text
import syslog

def log(msg):


from_email = GMAIL_ADDRESS
to_emails = [""]  # cell phone address

msg_subject = "OK: UPS Power Recovered"
msg_text = "Auto Notification"


msg = email.mime.text.MIMEText(msg_text)
msg['Subject'] = msg_subject
msg['From'] = from_email
msg['To'] = ", ".join(to_emails)
s = smtplib.SMTP_SSL('', '465')
s.sendmail(from_email, to_emails, msg.as_string())

Finally, we test the scripts locally to make sure the email notification is sent.  If everything looks good, test a power failure by disconnecting the UPS from the wall.  Within a few seconds, the apcupsd daemon should trigger the onbattery event and our email should be sent.  Now we will immediately know the next time the UPS looses wall power.

So, what if the power loss is not local to just the UPS?  An external monitoring service could be used.  Something like Nagios running from the cloud works great for this, but I will save that for another time.