YMMV

* your mileage may vary

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

RTMPDUMP Usage

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

Monday, 28 April 2014

EXNOR Gate

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?
sync

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:

NAND Gate


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:

NOT GATE

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

whatever

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