Author Archives: Jay

Roomba wiggle behavior, fixed

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My iRobot Roomba 4150 started to exhibit a behavior that I hadn't seen before. After starting up, the robot would "wiggle" as it went forward for a few feet, then turn, then move forward a few more feet while wiggling. After a few turns, it would stop and issue a double "uh-oh" sound. After cleaning and removing the vacuum brushes, the behavior was still hapening, so I decided it must be a problem with the sensors or motors on the robot. The robot's wheels would still turn manually, and they would pop up and down into the body as normal. I tried cleaning the clif sensors and that didn't fix the problem. Finally, I blew compressed air into the drive wheel compartment and that fixed the problem. Aparently, the rotary encoders on one of the wheels had gotten jamed up with dirt. 

The iRobot website did mention an OSMO update that is supposed to fix this issue, but according to the serial number on my roomba, it had already received the update. I guess removing the debris from the wheel is the better solution.

Laptop Battery Refill update

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I refilled the Li-ion cells in my laptop battery about 18 months ago.The battery has worked as expected since then. The only "special" treatment this battery gets is that it travels in my laptop (as opposed to being the extra battery in my backpack) when traveling through TSA security checkpoints. (I figure it's better the have the battery with the fully applied IBM label sticker visible in the backpack, and the battery where I pulled off the label sticker to dissasemble it safely integrated with the laptop.) 

Laptop Battery

Over the last 18 months, the battery capacity has reduced itself to 44% of the original value (This happens with LiIon cells as they age). My last full capacity ACPI reading is now  21060 mWh, and provides 1-2 hours of working time on my IBM X31 Thinkpad. In a few more months it will be time to replace the Li-Ion cells again. Luckly, a friend gave me an IBM T60 extended battery (containing 8 cells) that had failed. When I took it appart, it appeared that 6 of the cells worked fine, and two of the cells were dead (killing the entire battery). TaDa! 6 free replacement cells! 

Who watches the watchmen?

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A system downtime announcement I received today (slightly anatomized to protect the guilty):

Summary:

 

On Tuesday, July 1, 2008, at approximately 6:30 PM, the XXXX XXXXXXX server instance, which monitors the availability of XXXX servers and network devices, went offline.  This outage was not noticed until Monday, July 7, 2008.  After discovering the outage, the server was brought back online and was again monitoring services at 6:00 PM on July 7.

 

If you have any questions, please contact the XXXX Help Desk (XXXXXXXXXXXX).  Thank you.

Motofone F3 (North American version)

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I purchased a north American version of the Motofone F3 (Manufactured in Brazil), which operates on the 850/1900 Mhz GSM bands (used almost exclusively in North America) for $34 including S/H from dakmart.com. After plugging my SIM card in the phone it reported that it was on the AT-T network. My original Motofone F3 from India worked only on the 900/1800 bands, and wouldn't work on the AT&T network (or any other North American network). 

Continue reading →

Compressive Sampling: Beating the Nyquist Limit for certain signals

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Compressive Sampling is a new field of sensing theory that sidesteps the traditional Nyquist sampling limit. The Nyquist limit is an information theory result that says to perfectly capture a signal which is bandwidth limited at a certain frequency, X, you must take 2 times X samples per second.  So for example, if you want to perfectly detect a 20Hz sine wave, you must take 40 samples a second. To perfectly represent audio that humans can hear (typically understood to be sounds in the 20-20,000Hz range) we must use 40,000 samples per second (40kHz). CD audio uses 44.1kHz, and professional audio systems typically sample at 48kHz a second.  [Note that the number of samples per second has nothing to do with the quantization, or accuracy of the samples, so audio that is sampled at 20 bits per sample has more information (and less noise) than audio sampled at 16 bits per sample.] Continue reading →

Encrypted home directory with Ubuntu 8.04

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 My encrypted home directory worked  well with 8.04, I only had to make one change caused by the new xml format of the pam_mount.conf.xml file as follows:

<volume user="summetj" fstype="crypt" path="/dev/sda6" mountpoint="/home/summetj"         options="cipher=aes" fskeycipher="aes-256-ecb"         fskeypath="/home/summetj.key" />

After I installed 8.04 from scratch I had to mount the directory and chown the files to the new user.

MythTV / MythDVD movie ripping / playback problem (Solved!)

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I have used Myth to rip a large number of my DVD's to AVI files (using either the Excellent or Good setting).  Now that I am starting to play back the movies, I have found something that is very troubling.

On many of the movies, the first 95% of the movie (e.g. 1:13 min of a 1:26 movie) plays flawlessly. However, near the end of the movie, the audio and video starts to speed up and get jerky. (Audio/video sync is also thrown off.) Continue reading →

Connecting to non-broadcasting SSID networks with IPW2200

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I have been having problems connecting to a wireless network that does not broadcast its  SSID. (A so-called "hidden" network.) I am using an Intel IPW 2200 802.11b/g mini-pci wireless card that uses the ipw2200 wireless module.

I found that reloading the ipw2200 module before attempting to connect to the network fixed my problems (but only if I put a pause between the unload/load/connect sequence).  I use wifi-radar to manage my wireless connections, and was able to call my unload/reload script using its "before" connection command.

The script is simply:

sudo rmmod ipw2200
sleep 1
sudo modprobe ipw2200
sleep 1 

This does add two seconds to the connection time, but this is not a terrible penalty to pay as without the above pause the connection would usually only work about 25% of the time. 

DPMS monitor control via remote control on Myth TV

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I am using an LCD monitor as the display for my MythTV box, connected via an analog RGB (a.k.a. VGA) cable. This allows me to use DPMS (Display Power Management Signaling) to turn the monitor on and off from the MythTV box.

Instructions for setting this up with MythTV are here , but I found that I had to make a few changes to get things to work correctly. I modified one line of the shell script  as follows: 

STATUS=$( xset -q | grep "Monitor is" | awk '{print $3}' )

To trigger the monitorpowerbutton.sh script, I placed the following into my /etc/lirc/lircrc file:

begin
 prog =  irexec
 button = TV_POWER
 repeat = 4
 config = /usr/local/bin/monitorpowerbutton.sh
end

Now my TV_POWER button toggles the power state of the monitor! 

Fixing a missing bluetooth icon, battery charge indicator, and update notifier in Ubuntu

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Notification Icons

For the last week my battery indicator and bluetooth icons had been missing from my top panel in Ubuntu. When I did Bluetooth stuff the pop-up "speaker balloons" from the bluetooth applet would still appear at the corner of my screen, but the Bluetooth applet itself was "invisible". I finally figured out that what I was missing was a "Notification Area" for these applets to "live". Right-Clicking on the Panel, Selecting "Add to Panel" and then adding the "Notifcation Area" (from the Utilities category) fixed my problems. Indeed, I then found out that the Software Update notification icon had been trying to tell me about software updates, but I hadn't seen it, so I had to install several software updates!