Sunday, January 15, 2017

BeagleBone Green Wireless as a LAMP Server

This post demonstrates how to configure a BeagleBone Green Wireless (BBGW) first for WiFi tethering and then as a LAMP server.  For context, I have an IoT project (not described here) which uses the BBGW for data collection which can be examined using a web browser.

Flash your BBGW w/the latest image.  I am using "Jessie for SeeedStudio BeagleBone GreenWireless" (bone-debian-8.6-seeed-iot-armhf-2016-11-06-4gb.img).

After updating the BBGW image, log in to configure WiFi using connmanctl(1), there are example instructions in /etc/network/interfaces.

Now that you have internet connectivity, update the software using apt-get(8):
  • "apt-get update"
  • "apt-get upgrade"
Perform a gratuitous reboot for luck.

When the BBGW returns from reboot,  you should detect a fresh WiFi SSID in the form "BeagleBoneXXXXXX" where XXXXXX are integers.  This SSID was created by wifidog which is part of the BBGW Debian distribution.  

I don't need a captive portal for my purposes, so login to BBGW and invoke "apt-get remove wifidog-gateway" then reboot.

Now when the BBGW returns from reboot, you should detect a fresh WiFi SSID in the form "BeagleBone-XXXX" where XXXX are hex values representing part of the MAC address.

/etc/default/bb-wl18xx contains some tweakable parameters, such as SSID base.

/tmp/hostapd-wl18xx.conf is the actual hostapd(8) configuration file, note the wpa_passphrase "BeagleBone"

SoftAp0 is the WAP device:
root@beaglebone:/etc/default# ifconfig SoftAp0
SoftAp0   Link encap:Ethernet  HWaddr b0:d5:cc:ff:65:be  
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::b2d5:ccff:feff:65be/64 Scope:Link
          RX packets:5220 errors:0 dropped:3 overruns:0 frame:0
          TX packets:703 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 

          RX bytes:1328274 (1.2 MiB)  TX bytes:122059 (119.1 KiB)

From your laptop, connect to the BeagleBone device just as you would any other WAP.

Apache is configured for port 8080.  Verify you can connect to apache2(8) by visiting with your browser.

Assuming happy browser response, you now have a BBGW ready for a LAMP stack.  Note that the BBGW still has internet connectivity through wlan0 as configured earlier.

Now install mysqld(8) by invoking "apt-get install mysql-server" - when finished, verify a happy installation using mysql(1) and ensure you can at least login to mysqld(8).

Now install PHP, et al by invoking "apt-get install php5 libapache2-mod-php5 php5-mysql" - when finished, verify a happy installation by placing the usual phpinfo script into /var/www/html and visiting w/a browser.

Wednesday, December 28, 2016

Temperature Sensing w/BeagleBone Black and Adafruit PT100 RTD

Here is a simple example of collecting temperature w/BeagleBone Black (BBB) and the Adafruit PT100 RTD temperature sensor.  The PT100 sensor resistance varies directly w/temperature.  I can measure voltage drop across the PT100 sensor using an analog to digital converter (ADC) on the BBB and discover the temperature.

The BBB offers eight 12 bit ADC inputs.  ADC values range from 0 to 4096 (2^12).  Reference voltage is 1.8VDC.  Schematic below indicates Vref is on P9/pin 32, and the ADC input is P9/pin 39.  ADC ground (P9/pin 34) is tied to P9/pin 1 ground.  

My use case ranges from 0C to an upper bound of 400C.  The temperature sensor offers a resistance of 100 ohms at 0C and then .385 ohm per degree C or (in this case) a maximum  resistance of 100 + 400 * 0.385 = 254 ohms.

Given that Vref = 1.8 VDC and Rmin = 100 ohms, the current at minimum resistance is 18mA (this is a problem).  To mitigate loading, I added a LM358 op-amp as a voltage follower.  Put another way, simply reading the PT100 voltage drop might damage the BBB so I decide for additional circuitry as insurance.  

I want to use the temperature sensor as half of a voltage divider.  What value for the other half?  Old school teaches that R = sqrt(Rmin * Rmax) = sqrt(100 * 254) = 160 ohms.  Amazingly, I had a 160 ohm resistor available.

Schematic of temperature sensor demonstration

My PT100 came w/three wires ending w/a blue and two red terminals.  I only needed the blue and one of the red terminals.

To enable analog inputs requires some configuration.  This example uses Debian 7 image (bone-debian-7.11-lxde-4gb-armhf-2016-06-15-4gb.img).

root@beaglebone:~# echo $SLOTS
root@beaglebone:~# cat $SLOTS
 0: 54:PF--- 
 1: 55:PF--- 
 2: 56:PF--- 
 3: 57:PF--- 
 4: ff:P-O-L Bone-LT-eMMC-2G,00A0,Texas Instrument,BB-BONE-EMMC-2G
 5: ff:P-O-- Bone-Black-HDMI,00A0,Texas Instrument,BB-BONELT-HDMI
 6: ff:P-O-- Bone-Black-HDMIN,00A0,Texas Instrument,BB-BONELT-HDMIN
root@beaglebone:~# echo "BB-ADC" > $SLOTS
root@beaglebone:~# cat $SLOTS
 0: 54:PF--- 
 1: 55:PF--- 
 2: 56:PF--- 
 3: 57:PF--- 
 4: ff:P-O-L Bone-LT-eMMC-2G,00A0,Texas Instrument,BB-BONE-EMMC-2G
 5: ff:P-O-- Bone-Black-HDMI,00A0,Texas Instrument,BB-BONELT-HDMI
 6: ff:P-O-- Bone-Black-HDMIN,00A0,Texas Instrument,BB-BONELT-HDMIN
 7: ff:P-O-L Override Board Name,00A0,Override Manuf,BB-ADC

To read an ADC sample:
root@beaglebone:~# cd /sys/bus/iio/devices/iio:device0
root@beaglebone:/sys/bus/iio/devices/iio:device0# ls
dev              in_voltage2_raw  in_voltage5_raw  name       uevent
in_voltage0_raw  in_voltage3_raw  in_voltage6_raw  power
in_voltage1_raw  in_voltage4_raw  in_voltage7_raw  subsystem
root@beaglebone:/sys/bus/iio/devices/iio:device0# cat in_voltage0_raw

For verification, I placed the PT100 in a pan of water and heated it to boiling while reading BBB ADC (voltage) values every 5 degree C (from cooking thermometer), which yields this graph (circles are samples, line is regression model).

Graph illustrates temperature change is linear (and suggests a conversion model).  

To convert ADC to temperature use: 822 - 0.329512(ADC value)

Table (below) illustrates observed vs calculated temperatures.  Real world rarely match calculated world, but these values seem close enough for my intended application.

ADCObserved CCalculated C

Thursday, December 22, 2016

AWS IoT and BeagleBone Green Wireless

This post demonstrates how to configure a BeagleBone Green Wireless for Amazon Web Services "Internet of Things" using the AWS CLI.

The ingredients:
  • AWS Account
  • BeagleBone Green Wireless (BBGW)
    • Working WiFi
    • Flashed w/image bone-debian-8.6-seeed-iot-armhf-2016-11-06-4gb.img
    • apt-get update
    • apt-get upgrade
Install AWS CLI on BBGW.  Perform the following steps:
  • Create a IAM user for the BeagleBone
    • download the access key ID/secret access key
  • Install AWS CLI
    • pip install awscli
  • Configure AWS CLI (using the access key ID/secret access key from above)
    • aws configure
  • Verify AWS CLI installation by performing simple command
    • aws s3 ls (s3 directories are returned)
Generate security certificates:
  • mkdir aws_certs
  • cd aws_certs
  • openssl genrsa -out privateKey.pem 2048
  • openssl req -new -key privateKey.pem -out cert.csr
  • aws iot create-certificate-from-csr --certificate-signing-request file://cert.csr --set-as-active > certOutput.txt
  • grep certificateId certOutput.txt
  • aws iot describe-certificate --certificate-id <certificateId from last step> --output text --query certificateDescription.certificatePem > cert.pem
Create a policy and attach generated certificate:
  • Create policy document (policy.doc)
    "Version": "2012-10-17",
    "Statement": [{
    "Effect": "Allow",
    "Resource": ["*"]
  • aws iot create-policy --policy-name PubSubToAnyTopic --policy-document file://policy.doc
  • grep certificateArn certOutput.txt
  • aws iot attach-principal-policy --principal <certifcateArn from last step> --policy-name "PubSubToAnyTopic" 
At this point, you should be able to see the certificates/policy in the AWS console.  From the AWS IoT page, select "certificates" or "policies".
Alternatively, ask for certificates using AWS CLI:
  • aws iot list-certificates
Register your BeagleBone (thing) and attach to Principal (policy):
  • aws iot create-thing --thing-name bbgw
  • aws iot attach-thing-principal --thing-name bbgw --principal  <certifcateArn from previous step>
At this point you should be able to see the thing in the AWS console.  From the AWS IoT page, select "Registry/Things"
Alternatively, ask for things using AWS CLI:
  • aws iot list-things
Update BBGW status:
  • aws iot update-thing --thing-name bbgw --attribute-payload attributes={key1=value1}
Verify update:
  • aws iot list-things

Sunday, December 18, 2016

Infrared "break beam" detection using BeagleBone Black and Adafruit 2167

Here is a simple example of monitoring a infrared (IR) light beam w/BeagleBone Black.  There are many use cases for IR break beam sensors and for US $1.95 the Adafruit 2167 is an excellent choice.

The example provided by Adafruit is for the Arduino.  Here is a simple example using the BBB.

Schematic of "break beam" demo.
  Any GPIO will do.  Below is a runtime example from a BBB using Debian 7 (wheezy).  Note that "value" contains a 1 when the IR beam is detected and a 0 when I block the beam.

root@beaglebone:~# cd /sys/class/gpio
root@beaglebone:/sys/class/gpio# echo 115 > export
root@beaglebone:/sys/class/gpio# cd gpio115
root@beaglebone:/sys/class/gpio/gpio115# echo in > direction
root@beaglebone:/sys/class/gpio/gpio115# cat value
root@beaglebone:/sys/class/gpio/gpio115# cat value

Sunday, April 24, 2016

AWS API Gateway and Lamba (Python) Demonstration

I have a customer interested in AWS API Gateway and Lambda (Python), so I created a small demonstration application to explore this option.

The resulting application is a simple 4 function calculator web service.  There is significant overlap between this demo and the LambdaGate example provided by AWS.  This application is different because:
  • Employs Cloud Formation as much as possible
  • Python (instead of node.js) Lambda function

Sunday, June 1, 2014

Google App Engine Development Environment on Mavericks w/IntelliJ and maven

Google App Engine/Java is an interesting platform which does not seem to get the same attention as AWS EC2.  I work on contract and it is a rare day that someone asks me to work on a GAE project while AWS EC2 is extremely common.  I understand there are many reasons for this, and (IMO) one reason is the vast quantity of stale/incomplete blogs posts which make GAE/J difficult to learn and adopt.  I am certain this post will also become stale in the future, so ensure the products I am using match your goals before investing.  Today is 1 June, 2014 and the tools I want to employ are:
  1. OSX 10.9
  2. Google App Engine 1.9.5
  3. Java 1.7
  4. Maven 3.1
  5. IntelliJ Idea 13
  6. Objectify 5
Note: example application is located on github.

The first issue you may encounter as a OSX user is that GAE requires Java 1.7 and you might still be on Java 1.6 - DO NOT get the latest Java 1.7 (which is currently 1.7.0_60) because of bug JDK-8025876.   Instead select Java 1.7.0_25 - there has been much discussion about this issue, here is an example from Stack Overflow.

You should be able to obtain results similar to this:
gsc@duckman:72>java -version
java version "1.7.0_25"
Java(TM) SE Runtime Environment (build 1.7.0_25-b15)
Java HotSpot(TM) 64-Bit Server VM (build 23.25-b01, mixed mode)

Now that your system is working on Java 1.7, you should ensure that maven is aware of the update.  Simply updating $JAVA_HOME was not sufficient and I also needed to tweak .mavenrc - once again Stack Overflow to the rescue.  

You should be able to obtain results similar to this:
gsc@duckman:73>mvn -v
Apache Maven 3.1.1 (NON-CANONICAL_2013-11-17_20-36_gsc; 2013-11-17 20:36:09-0800)
Maven home: /Users/gsc/local/apache-maven-3.1.1
Java version: 1.7.0_25, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.7.0_25.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.9.3", arch: "x86_64", family: "mac"
At this point, java and maven are ready.  If you have not already done so, download the latest Google App Engine SDK (currently 1.9.5) and install it on your system.  Point to the GAE installation with $APPENGINE_HOME

Google provides the guestbook tutorial which has been updated recently (note the EAR directory in addition to the original WAR).  The application skeleton is generated from maven with features incrementally added through the tutorial.  Instructions are reliable until until runtime when Google shows the old (now wrong) command to start/deploy on a local development server.  Assuming you have this directory structure:
total 32
drwxr-xr-x  8 gsc  staff   272 Jun  1 10:21 ./
drwxr-xr-x  7 gsc  staff   238 Jun  1 10:38 ../
-rw-r--r--  1 gsc  staff   106 Jun  1 10:21 .gitignore
-rw-r--r--  1 gsc  staff   121 Jun  1 10:21
drwxr-xr-x  6 gsc  staff   204 Jun  1 11:47 guestbook-ear/
drwxr-xr-x  6 gsc  staff   204 Jun  1 11:47 guestbook-war/
-rw-r--r--  1 gsc  staff   583 Jun  1 10:21 guestbook.iml
-rw-r--r--  1 gsc  staff  1009 Jun  1 10:21 pom.xml

The correct command to start/deploy on a local development server is:
gsc@duckman:90>mvn -pl guestbook-ear appengine:devserver                                 
When you see "[INFO] INFO: Dev App Server is now running" then you should be able to visit the guestbook application at http://localhost:8080 and the GAE console is on http://localhost:8080/_ah/admin (guestbook screenshot below)

At this point, you have a simple, working application which you can compile and deploy using command line arguments.  Now I bring IntelliJ 13 into the mix.

First you must configure IntelliJ for your freshly installed Java 1.7 - start IntelliJ and from the splash panel select "Configure"->"Project Defaults"->"Project Structure" and the goal is a display like below.

Now we need a project.  You can continue to use the original guestbook application or consider my derivative version from github.  If you are interested in a quick introduction to objectify then use my version.

IntelliJ can be challenging to configure, YMMV but in my experience the tutorials and help are rarely up to date even for the "ultimate" version.  Once again, Stack Overflow is probably your best resource for assistance.

Ensure you have the "GAE Integration" plugin enabled.  The following screenshots might help in comparing your environment from mine.
The proof is your success in being able to compile and deploy to your local development server from within IntelliJ.  Attempt it now using the "make" triangle in the top right toolbar.

At this point you should now be able to work on a GAE/J application using IntelliJ (including the debugger).  Only objectify remains to be explored.

The original guestbook sample application uses the DatastoreService for persistence in two spots: reading guestbook entries within guestbook.jsp and writing guestbook entries within

To use objectify I have added as an Entity and as a DAO.  I also modified guestbook.jsp and to use the DAO (and objectify) rather than the datastore directly.

This concludes my short tour of making a small GAE project and I hope it saved you some time.

Sunday, April 27, 2014

Hybrid Android Applications w/WebView

Many Android applications look entirely native but have at least a portion of the UI implemented using a WebView to display HTML and JavaScript.  (In this context, "native" means a UI created in the traditional Java/XML approach and not the NDK).

This post illustrates the use of WebView along w/WebViewClient and WebChromeClient.  I have created a small demonstration application ("AndroidWebView") which is available on github.

AndroidWebView has four tabs to demonstrate different use cases (screenshots below).

The first tab ("About") illustrates the simple use case of reading a locally stored HTML file into a WebView.  Using HTML is a frequent solution for non-interactive, wordy content such as T&C, EULA or perhaps application help pages.  As you can see was extremely simple to implement.

"About" tab selection
"Client" tab selection
The second tab ("Client") reads a remote web page and manages interaction w/the remote server using a WebViewClient.  Again ClientFragment,java is small and simple. reacts to events such as "page started", "page finished", "authorization requests", "errors", etc.  I have implemented the interesting methods to write log messages so we can view the progress using "adb logcat".

The received web page (above, on the right) and there are four navigation buttons (i.e. "Contact", "News", "Products", "Services") which are implemented as HTTP HREF(s).  Within DemoWebViewClient.shouldOverrideUrlLoading() I have arranged for the "News" button to invoke rather than perform the usual HTTP GET.  This illustrates the use case of HTML content invoking an Android View.

It is useful to view the log output ("adb logcat") when viewing the "Client" tab.  When reviewing the log, you will see the various requests necessary to render the page.  This illustrates that you can detect and perhaps alter the content, or react to certain events.  The log output should look similar to this:

DemoWebViewClient(20221): interceptRequest:
DemoWebViewClient(20221): pageStarted:
DemoWebViewClient(20221): load:
DemoWebViewClient(20221): interceptRequest:
DemoWebViewClient(20221): load:
DemoWebViewClient(20221): interceptRequest:
DemoWebViewClient(20221): load:
DemoWebViewClient(20221): interceptRequest:
DemoWebViewClient(20221): load:
DemoWebViewClient(20221): interceptRequest:
DemoWebViewClient(20221): load:
DemoWebViewClient(20221): interceptRequest: //deleted
DemoWebViewClient(20221): load: //deleted
DemoWebViewClient(20221): pageFinished:

The third tab ("JS") illustrates interaction w/JavaScript. creates a WebChromeClient which enables support like connecting the JavaScript console to write via the Android log or report loading progress.  If you wish to use JavaScript Alert() rather than an Android View, you will need to use WebChromeClient.onJsAlert() (which I have implemented for this purpose).  The "generateAlert" button produces a JavaScript alert. relies upon to expose Java methods which can be invoked from JavaScript.  I have implemented simple examples to illustrate using Android logging or return a String to JavaScript.  The "@JavascriptInterface" is limited in many ways regarding parameters and return results: primitives and Strings usually work but you will want to experiment before promising complicated arguments.  Note that generatePrimes() returns a String which contains a JSON formatted array, and this is a successful approach.  Pressing "generateLog" will cause an Android log message to be written (visible via "adb logcat").  "generatePrime" invokes a Java based prime number generator and returns the results as a JSON formatted String.

What about the use case of Java invoking JavaScript?  This is also possible and pressing "Invoke JavaScript" shows how.  "Invoke JavaScript" is a standard Android button which invokes WebView.loadUrl() for bridge.html which writes a log entry back to Java.

The fourth tab ("Simple") demonstrates the trivial use case of reading a remote file without WebViewClient or WebChromeClient.