btodorov@blog

Wireless temperature sensor with Raspberry Pi

2013-01-14T11:16:00.001+02:00

Finally got some time to play with the Raspberry. Behold the wireless temperature sensor :D

The sensor itself is LM95071. Temperature is read through SPI. The only problem was that after the first read the sensor was put in shutdown mode... I guess this is because the SPI is full duplex and the SI/O pin was left dangling during WR to the sensor (even though I was only reading from it...). The solution was to add pull-down resistor to the SI/O pin (the additional resistor on the picture).

I have Apache web server on the RPi and I'm using WUSB54GC wifi dongle to transmit the temperature over the internet :)

WiFi dongle on Raspberry Pi

2012-08-06T20:07:00.002+03:00

A little guide how to use Linksys WUSB54GC WiFi dongle on Raspberry Pi (Raspbian “wheezy” images). The dongle is pretty old but I used it just for the test :)

(1) You need self-powered USB hub!
(2) Plug the dongle in the hub:

pi@raspberrypi:~$ dmesg
[ 111.915950] usb 1-1.3.2: new high speed USB device number 5 using dwc_otg
[ 112.216207] usb 1-1.3.2: New USB device found, idVendor=13b1, idProduct=0020
[ 112.216240] usb 1-1.3.2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 112.216261] usb 1-1.3.2: Product: Compact Wireless-G USB Adapter
[ 112.216290] usb 1-1.3.2: Manufacturer: Cisco-Linksys
[ 112.311511] cfg80211: Calling CRDA to update world regulatory domain
[ 112.495964] usb 1-1.3.2: reset high speed USB device number 5 using dwc_otg
[ 112.978042] ieee80211 phy0: Selected rate control algorithm 'minstrel_ht'
[ 112.981551] Registered led device: rt73usb-phy0::radio
[ 112.982146] Registered led device: rt73usb-phy0::assoc
[ 112.982727] Registered led device: rt73usb-phy0::quality
[ 112.987435] usbcore: registered new interface driver rt73usb

We can also see the drivers are loaded:

pi@raspberrypi:~$ lsmod
Module Size Used by
...
rt73usb 23490 0
rt2x00usb 12077 1 rt73usb
rt2x00lib 43890 2 rt2x00usb,rt73usb
mac80211 253889 2 rt2x00lib,rt2x00usb
cfg80211 180459 2 mac80211,rt2x00lib

(3) wlan0 interface is automatically created:

pi@raspberrypi:~$ ifconfig
wlan0 Link encap:Ethernet HWaddr 00:1d:7e:11:c4:56
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)

(4) To connect automatically to WiFi AP add this to /etc/network/interfaces:

auto wlan0
iface wlan0 inet dhcp
wpa-ssid <AP-SSID>
wpa-psk <KEY>

(5) Restart networking:

pi@raspberrypi:~$ sudo /etc/init.d/networking restart
Running /etc/init.d/networking restart is deprecated because it may not re-enable some interfaces ... (warning).
Reconfiguring network interfaces...Internet Systems Consortium DHCP Client 4.2.2
Copyright 2004-2011 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/wlan0/00:1d:7e:11:c4:56
Sending on LPF/wlan0/00:1d:7e:11:c4:56
Sending on Socket/fallback
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 7
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 9
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 12
DHCPREQUEST on wlan0 to 255.255.255.255 port 67
DHCPOFFER from 192.168.32.1
DHCPACK from 192.168.32.1
bound to 192.168.32.104 -- renewal in 32936 seconds.
done.

Done!

pi@raspberrypi:~$ dmesg
[ 374.243090] wlan0: authenticate with 00:b0:0c:4f:25:10 (try 1)
[ 374.244913] wlan0: authenticated
[ 374.307729] wlan0: associate with 00:b0:0c:4f:25:10 (try 1)
[ 374.312512] wlan0: RX AssocResp from 00:b0:0c:4f:25:10 (capab=0x411 status=0 aid=1)
[ 374.312540] wlan0: associated

pi@raspberrypi:~$ ifconfig
wlan0 Link encap:Ethernet HWaddr 00:1d:7e:11:c4:56
inet addr:192.168.32.104 Bcast:192.168.32.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:51 errors:0 dropped:0 overruns:0 frame:0
TX packets:37 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:10652 (10.4 KiB) TX bytes:4726 (4.6 KiB)

Try some ping:

pi@raspberrypi:~$ ping google.com
PING google.com (209.85.148.101) 56(84) bytes of data.
64 bytes from fra07s07-in-f101.1e100.net (209.85.148.101): icmp_req=1 ttl=56 time=34.7 ms
64 bytes from fra07s07-in-f101.1e100.net (209.85.148.101): icmp_req=2 ttl=56 time=46.4 ms
64 bytes from fra07s07-in-f101.1e100.net (209.85.148.101): icmp_req=3 ttl=56 time=45.8 ms
...

So for the test I left it pinging for some time. Haven't seen any issues till now :)

Next step: To avoid using self-powered hub find WiFi dongle with lower power consumption... :/

Raspberry Pi

2012-08-03T19:53:00.002+03:00

My long awaited Raspberry Pi finally arrived:

I tried it with Raspbian (wheezy) images:

One of the first impressions is that apparently there is absolutelly no power management (PM) - the board generates a lot of heat :(
Should search for images with some PM optimization (hope they exist).

Hmm... now must think of a good project :D

Touchscreen calibration in Android

2011-08-31T21:15:00.001+03:00

Another how-to. This time about touchscreen calibration for Android.

We assume you already have your touchscreen driver for your dev board and you've tested it with Android getevent (or the evtest tool) and you're sure it's giving the right coordinates to user space.

Next step before really using it is calibration ... which is real pain in the a** because Android doesn't provide a calibration tool. For the purpose we are going to use ts_lib.

To clone ts_lib package ported for Android use:

$ git clone git://tslibonandroid.git.sourceforge.net/gitroot/tslibonandroid/tslibonandroid

Then build it as normal Android package with "mm" (I assume you already know how to build Android... If no checkout this link for basics).
Copy all output files from the build to their corresponding places in the target dev board.

To create calibration file for the touchscreen boot the board, export the following environment variables

export TSLIB_TSDEVICE=/dev/input/event1
export TSLIB_CONFFILE=/system/etc/ts.conf
export TSLIB_CALIBFILE=/system/etc/pointercal
export TSLIB_PLUGINDIR=/system/lib
export TSLIB_CONSOLEDEVICE=/dev/tty
export TSLIB_FBDEVICE=/dev/graphics/fb0

(see also Android.mk in ts_lib sources)

and then run the newly built ts_calibrate tool.

Now we must apply this patch to make Android use the calibration file we created.

Rebuild Android services and you custom touchscreen must now work properly :) Hope it was useful!

P.S. the above was tested on Android Eclair with resistive touchscreen.

Java attempt

2011-06-23T20:04:00.005+03:00

Today I made my first java application using NetBeans IDE. Hurray! :)

It converts Celsius to Fahrenheit and the opposite ... *quite* n00b-ish :D

How it looks:

The jar file: CelsiusConverter.jar

- - -

Git cheat sheet

2011-04-29T15:40:00.000+03:00

Yet another git help :)
This time cheat sheet (mostly for beginners):

Dropbear sshd on Android device

2011-04-28T22:14:00.003+03:00

Recently I needed to have SSH connection with Android development board but since no SSH daemon is included in the official Android release I had some troubles finding the right way to do it.

The following guide was tested on OMAP3 development board with Android Eclair but should be working on any (rooted/unlocked) phone with Android.

Instructions how to run dropbear sshd on Android device:

First you fetch the latest Dropbear sources:

git clone git://android.git.kernel.org/platform/external/dropbear.git

Since the Android has different paths, no password support, etc. we must fix this in the original sources by applying the patch found here: http://pastebin.com/f3dedc5e7

...the only problem is that it's for older version of Dropbear so we must try to apply it manually :(

After patch was applied build with:

./configure --host=arm-none-linux-gnueabi --disable-zlib

make CC=arm-none-linux-gnueabi-gcc

In case you're unable to apply the patch correctly or something went wrong with the build here is a archive with prebuilt binaries (dropbear, dropbearkey, dropbearconvert):

>>> dropbear.tar.bz2

(Another guide how to build Dropbear for Android can be found @ http://teslacoilsw.com/dropbear)

Install:

To install dropbear on the desired gadget copy the binaries to some custom dir, e.g. /dropbear.

Setup the Server (Android):

Generate a RSA server key using dropbearkey:

dropbearkey -t rsa -f dropbear_rsa_host_key

Then create a dir /data/dropbear and copy dropbear_rsa_host_key there.

Test dropbear:

/dropbear/dropbear -r dropbear_rsa_host_key -F -E -v -s

This should show you the debuglog (the (-F) option means non-daemon mode).

Now we need to generate a key-pair for the client to connect with (Dropbear is run with the option -s (no-password) because there is no password support in Android):

//generates a private key

dropbearkey -t rsa -f /dropbear/id_rsa

//extract the public-key:

dropbearkey -f /dropbear/id_rsa -y > /dropbear/id_rsa.pub

We need to create /data/dropbear/.ssh and cat the public-key to authorized_keys:

mkdir /data/dropbear/.ssh

cat /dropbear/id_rsa.pub > /data/dropbear/.ssh/authorized_keys

IMPORTATNT: Check the perms of /data/dropbear and make sure they are *only* readable/writable by root!

Setup the Client (Ubuntu):

As dropbear and openssh use different key formats we first need to convert id_rsa (private key) to openssh-format:

./dropbearconvert dropbear openssh /dropbear/id_rsa /dropbear/id_rsa_openssh

Now move id_rsa and id_rsa_openssh to your desktop (e.g. to your home dir).

Before establishing connection gadget's USB interface should be UP:

busybox ifconfig usb0 up 192.168.1.2

(yes, busybox must be installed on the Android device...)

Finally connect to the device:

ssh -i id_rsa_openssh <device-ip>

You can use -vv for both the client and the server to see debug info and fix whatever is wrong.

Setup the Client (Windows XP):

The only difference is that we use different SSH client. I used PuTTY.

So...

- boot the board/phone

- connect PC with board with USB cable and wait for auto install

- set IP address (TCP/IP settings) in the automatically created USB Ethernet connection

- copy auth. keys generated with dropbear

- convert OpenSSH key to "PuTTY" key (ppk) using PuTTYGen

- open PuTTY and set remote IP/Port to connect to

- use SSH key generated with PuttyGen: Connection -> SSH -> Auth -> select key

- connect!

NOTE: The above is extended/edited version of the original guide @ http://cri.ch/sven/doku.php/blog/running-dropbear-on-android

Useful git commands

2011-04-19T17:39:00.002+03:00

Some git commands that I found useful...

To remove all untracked files and dirs (aka "uber clean"):

$ git clean -f -d -X

For more useful/clear git log ouput:

$ git log --oneline --decorate

or better use the following command:

$ git log --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit --date=relative

You can add it as alias in ~/.gitconfig :

[alias]

lg = log --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit --date=relative

More @ http://cheat.errtheblog.com/s/git

Eee PC 901 paint job

2011-04-18T22:58:00.002+03:00

At laaast! The 2-year warranty on my Eee PC 901 netbook has expired. Since I bought it its pearl white color was torture to my eyes (there were only white ones left at the store) but now I can finally pain it BLACK >:]

The disembowelment was kind of hard but here is the result:

Actually I was a bit surprised by of the assembly quality. Asus did a good job :)

Next I took all parts of the case, mask all necessary holes with duct tape (the mic, all the LED holes, etc.) and sand the parts a little. Then I removed any grease left and applied three layers of paint (with 2h for drying before applying the next layer).

I left it for 24h to dry and here is it (I spent two hours assembling the damn thing):

Maybe not quite as I expected but it looks nice. :) Though I *should* have bought more expensive paint.

I left the battery white but maybe (someday) I'll paint it too. And maybe order some black keyboard & pad from ebay .... :)

Encode/Scale video with MEncoder

2011-04-13T22:55:00.003+03:00

The only thing I don't like about my old Canon S3 IS camera is that it records video without compression. Meaning that 4min 640x480/30fps vid is about 512MB...

I spend some time playing with MEncoder ("...a free command line video decoding, encoding and filtering tool released under the GNU General Public License" and a really *great* tool) and found a way to encode (or scale) my videos from Linux command line:

Encode from Canon RAW (acceptable quality):

$ mencoder INPUT.mpeg -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=1800:mbd=2:trell=yes:v4mv=yes -o output.avi

Scale video:
$ mencoder INPUT.mpeg -vf scale=320:240 -oac copy -ovc lavc -lavcopts vcodec=mpeg4 -o OUTPUT.mpeg

More info about MEncoder @ http://www.mplayerhq.hu/DOCS/HTML/en/mencoder.html

Create swap file in Linux

2011-04-13T10:55:00.004+03:00

Some time ago when I was working with a BeableBoard-like dev board I had troubles creating Linux swap file. After reading some guides over the internet I'd like to share this simple how-to (Ubuntu):

1) Create "empty" file (~537 MB):

$ dd if=/dev/zero of=/swapfile1 bs=1024 count=524288

2) Setup Linux swap area:

$ mkswap /swapfile1

3) Activate swap space immediately:

$ swapon /swapfile1

4) Add to fstab (optional):

/swapfile1 swap swap defaults 0 0

To test:

$ free -m

To deactivate:

$ swapoff /swapfile1

Hope that someone would find it useful :)

Different look for the Linux console

2011-04-12T21:57:00.008+03:00

//lol...first "official" post

If you're bored of the default color your Linux console or want to change the look of it checkout the following example (Ubuntu):

Edit ~/.bash.rc with:

PS1="\n\[\e[32;40m\]| \[\e[31;40m\]\H \[\e[32;20m\]\d \[\e[32;1m\]\t \[\e[1;33m\]\w\[\e[0m\]\[\e[32;40m\]\n| \[\e[37;40m\]\u\[\e[1;37m\] \\$ \[\e[32;1m\]\[\e[0m\]"

and

force_color_prompt=yes

Output:

Feel free to modify :)

Creation!

2011-04-12T21:18:00.002+03:00

Blog created.
Purpose yet unknown :)
Will post random stuff...