* your mileage may vary

Saturday, 28 June 2014

Beaglebone Black (BBB) setting GPIO Pins with devmem2

Access and setting GPIO Pins quickly using devmem2. Get devmem2 source and compile/build.

Friday, 27 June 2014

Beaglebone Black (BBB) with DS1302 Real Time Clock (RTC)

Code to read or write date & time to or from DS1302 RTC
Code is a merge of the RTC-RPi and tutorial from Derek
Molloy examples of accessing the GPIO on the BBB

Sunday, 8 June 2014

Beaglebone Black (BBB) Compile Kernel Locally

Steps I follow to compile BBB Kernel locally.  It takes about 5 hours to compile (make) on the BBB.  Use at your own risk (make a backup!).  Run as root to avoid disappointment.

Friday, 6 June 2014

Sunday, 1 June 2014

Garmin 405CX on Linux

Lots of different and confusing sites with different methods.  This one worked for me on Ubuntu/Mint


Beaglebone Black (BBB) Send Mail Via Gmail

Steps to set up mail sending via Gmail.  A Gmail account is required.

Friday, 30 May 2014

Beaglebone Black (BBB) Revision / Version & Serial Number From EEPROM

Some useful commands to pull information from the BBB
  • hexdump -e '8/1 "%c"' "/sys/bus/i2c/devices/0-0050/eeprom" -s 13 -n 3 2>&1

Beaglebone Black (BBB) with Realtek RTL8188CUS WiFi Adapter

The Realtek 802.11n WLAN Adapter is a troublesome little thing.  Two files need to be updated to make this work. In the end, the most predicable/stable situation is to assign a static IP address to the adapter.  I got my adapter from the PiHut for 6 quid. http://thepihut.com/products/usb-wifi-adapter-for-the-raspberry-pi

Thursday, 29 May 2014

nmap Script to Check for New Devices Connected to LAN

Steps to check for new "unknown" devices added to network.  I have it running in a crontab every 30 minutes.
Note: must be run as root/sudo to return valid MAC address from nmap command

Wednesday, 28 May 2014

Beaglebone Black (BBB) Cross Compile

The web site: http://eewiki.net/display/linuxonarm/BeagleBone+Black shows the instructions on how to compile from source for BBB.  The site is a bit flaky and not all the text is rendered and displayed (using Firefox!) so I've reproduced it here for convenience.  The only thing I've done it mde sure the all content is shown.  Full credit is attributed to Robert Nelson.

Sunday, 25 May 2014

Raspberry Pi Radio with 2.8 TFT Touch Screen

Update: Avoid upgrading to Jessie if possible.
Working details of how to setup a Pi-Radio using MPD/MPC Python and a TFT Touch Screen. 

Saturday, 24 May 2014

Beaglebone Black (BBB) with USB Sound Card (C-Media Electronics, Inc. CM106)

To play/stream music with the BBB and a USB sound card, the setup is very straightforward.

Beaglebone Black (BBB) Boot Process

The BBB boot process is actually a series of steps that can be control based on inputs.  Changing the inputs can change how it boots.  Just because an SD card inserted does not mean all the boot processes are originating from the SD card.

Thursday, 15 May 2014

Samsung SyncMaster S22B300 EDID

 /var/log $ xhost +
access control disabled, clients can connect from any host
 /var/log $ export DISPLAY=:0
 /var/log $ xrandr --verbose

Tuesday, 6 May 2014

Pull Up / Pull Down Resistor

Use a pull up or a pull down resistor to keep the digital pins from floating.  Pull up is tied to +V; pull down is tied to -V.

Saturday, 3 May 2014

Wednesday, 30 April 2014

Beaglebone Black (BBB) Network / Internet Connection via USB

on desktop:
sudo iptables -A POSTROUTING -t nat -j MASQUERADE
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward > /dev/null


sudo iptables -t nat -A OUTPUT -p tcp --dport 1935 -j REDIRECT
run video
sudo iptables -t nat -D OUTPUT -p tcp --dport 1935 -j REDIRECT

Monday, 28 April 2014


The output of an EXNOR input is low if either or but not both the inputs are high.
It is opposite of an EXOR.
2xSPDT switches and keep the wires parallel.

Truth table:

EXOR Gate - "Exclusive-OR"

The output of an EXOR input is high if either or but not both the inputs are high.
2xSPDT switches and cross the wires

Truth table:

Sunday, 27 April 2014

Beaglebone Balck (BBB) Default Keyboard & Time Zone

BBB default values for some items need to be configured depending on location.
For timezone run:
tzselect (and follow the menu choices)

Beaglebone Black (BBB) Debian Root Password

BBB default debian image ships without a root password.  To create a root password:

Beaglebone Black (BBB) Resize Partitions

BBB img files are usually about 1.6G and don't use all of the available disk space.  Use gparted or fdisk to expand the file system to use the full disk.  

Caution:  can be dangerous

Beaglebone Black (BBB) Copy img File Using DD

To copy a image file to a SD card use DD (also known as Disk Destroyer as it can wipe the hard disk if you don't pick the right device)

sudo dd bs=4M if=filename-of-image.img of=/dev/sd?

Saturday, 26 April 2014

NOR Gate

A NOR (NOT-OR) gate is equal to an OR gate followed by a NOT gate.  The output of a NOR gate is low if any of the inputs are high.
I use a relay, most sites I've seen use a transistor.

Truth table:


The output of a NAND gate is high if any of the inputs are low.  Sometimes referred to as a NOT-AND gate (equal to an AND gate followed by a NOT gate).
I use a relay, most sites I've seen use a transistor.

Truth table:


A NOT Gate (or inverted) switches high to low and vice-versa.  I use a momentary switch connected to a relay to flip the current on / off.

Truth table:

Beaglebone Black (BBB) Boot Chart

BBB boots in 23 seconds according to bootchart  (uSD boot)
(40 seconds with the GUI)

Beaglebone Black (BBB) Disable Debian Desktop GUI / LXDE / lightdm cmdline=systemd.unit=multi-user.target (for Jessie)

To disable the GUI in the Debian Desktop and just have a normal terminal login, put the following into /boot/uboot/uEnv.txt 
  • optargs=text (for Whezzy) 
  • cmdline=systemd.unit=multi-user.target (for Jessie)

Friday, 25 April 2014

4 Band Resistors Colour Codes


AND Gate

For an AND Gate, current runs in series so both A and B must be 1 for X to be 1

Truth table:

OR Gate

For an OR Gate, current runs in parallel so either A or B (or both) can be 1 for X to be 1

Truth table:

Thursday, 24 April 2014

Beaglebone Black (BBB) HDMI Debian X11/LDE Display Problem ?

I was having trouble to debug a problem related with the bootup process and the LDE GUI display.  I'm not really sure what the problem was or why this worked, but in the end it worked for me. I've posted this in the BBB forum but Google Groups is a headache.

On LED's

Normal LED's draw about 20mA
Rated between 2-3 volts depending on colour
  • White LED: 3.2V 25mA
  • Blue LED: 3.2V 25mA
  • Green LED: 2.1V 20mA
  • Red LED: 2V 15mA