Vex Servo Motor

Vex servo motors have a lot of good features. They are compact, powerful, and easy to mount and connect to things like gear shafts, beams, levers. I’ve been using micro controllers to operate these in previous projects, but decided to go old school and use a 555 timer. I really just want to do something to try out my new USB oscilloscope. I found this page with a couple of good plans.

wolfstone.halloweenhost.com

Breadboarding this was fairly easy and took just a few minutes.  I keep a lot of components around with breadboard wire already soldered, so that makes prototyping a lot faster.

Before I attached the motor, I verified that the circuit was performing as needed.  With the oscilloscope set to show 5 ms per division I could measure the minimum pulse width of 1.15 ms and a maximum width of 2.75 ms.

This seemed good enough to try, so I plugged in the motor.  The black wire is ground, the red (or orange) wire is positive, and the white wire is the signal (pin 3 on the 555).    I had nearly the full 100 degree rotation in the motor as I turned to potentiometer shaft back and forth from minimum to maximum.

Just for fun, I substituted a flex sensor for the potentiometer.  Not quite the same amount of rotation, but, I didn’t bother changing any other component values.

Servo Motor with Flex Sensor from Patrick Lewis on Vimeo.

Bill Gates at the Computer Bowl

My favorite Bill Gates moment ever. This comes from a show called the Computer Chronicles that aired sometime in 1993.

The man answering the question is Jean-Louis Gassee, one-time Apple executive, probably best known for BeOS.

The correct answer, BTW, was “The Obfuscated C Contest.”

MySQL firewall issues on Fedora

This is my experience with making a MySQL database on one server accessible to a mysql client on another server. While this issue has been addressed extensively, I think the solution to my problem was something that was not mentioned in any of the sources I searched.

Accessing the DB server worked on the local machine, but, this was the message I received when attempting to access the it on a remote host.

“ERROR 2003 (HY000): Can’t connect to MySQL server on. . .”

I eliminated some other things as potential causes right away. My permissions for the user and host were set properly. The MySQL server was not started with the “skip-networking” option set, and the server was not restricting TCP access to localhost.

Narrowing this down to a firewall issue was pretty straightforward. First, I stopped the firewall.

/sbin/service iptables stop

Then I tried again to access the DB server remotely and succeeded. When I restarted the firewall, the problem returned.

Searching on the net, I came across this recommendation in many places. Basically, a command to add an entry to open port 3306.

iptables -A INPUT -i eth0 -p tcp -m tcp –dport 3306 -j ACCEPT

I entered this but it still didn’t help. Then, I began to look at the iptables configuration with this command.

ipatables-save

This just writes the iptables entries to STDOUT. What I noticed was that the entry for port 3306 was preceded another line. Here is how the two lines appeared.

-A INPUT -j REJECT –reject-with icmp-host-prohibited
-A INPUT -i eth0 -p tcp -m tcp –dport 3306 -j ACCEPT

I sent the result of the ‘iptables-save’ to a file and then edited this file and switched the order of the two lines above. Then I restarted the firewall.

/sbin/services iptables restart

This worked and my databases have been accessible since.

Go bananas for bananas4apples!

Help out a friend of mine to get his blog off the ground.

In his words, “It’s a place to learn cool stuff about your Apple computer and Leopard.”

Check out the site at bananas4apples.

Extinguishing a kitchen fire

Bottom line is not to throw water onto this type of fire.

JavaScript Frameworks

Here are a couple of excellent post regarding the use of JQuery vs Mootools.

Three real good reasons to use JQuery, from a Mootools lover

The one real reason to not use JQuery