2010-01-17 Calibrate good times

We have a DT-470 temperature sensor in the cryostat of the project I'm currently working on. The problem is that our software is displaying the wrong readout. I'm trying to figure out how to display the correct value in Kelvin.

I've got the following to work with:

• The cryostat is filled with liquid nitrogen, which we know is around 77 K.
• The sensor was also read out when the cryostat was not cooled, so we have a combination of raw value (as read from electronics) and known temperature as well (room temperature, 20 degrees Celsius, is about 293 K).
• We've been provided with a data sheet from which a polynomial can be derived.
• The spec says we need to drive the sensor with a 10uA current, but in actuality, we drive it with a 12.368 uA current. I'm told this is not a big deal, because the difference in current is unlikely to cause a difference in warmth.
• The spec also gives us a lookup table to transform raw value to Kelvins
• Because of the way the sensor is read out, we need to apply an additional offset and factor (our electronics influence/amplify the readout).
• The sensor readout is linear for the range from 10 to 200 K, then follows a curve to 0 K.

The software has the ability to apply a polynomial to a raw value (i.e. a value that's read out from the electronics), as well as apply a user-configurable function to a value. That is usually used for convenience like electronics giving us a negative value, when we'd rather receive a positive value.

In this case, the polynomial is applied to correct the value for the way our electronics influence the raw value. Then, the user-configurable function is applied, which in this case is the polynomial that follows from the data sheet.

So the steps are:

• Remove the electronics and drive the sensor manually. Do we get the same value (raw) as we get from the electronics?
• Get the raw value, and see whether our first polynomial is OK (the first polynomial is a simple one, just an offset plus a factor). We can do this by looking up the raw value in the lookup table.
• Use that in-between value and check the lookup table to see whether the second polynomial is OK.
• The heating of the electronics board could also play a role, we need to check that as well and if so, correct the first polynomial.

2009-12-09 Installing Linux Google Chrome as a regular user

Early december 2009, Google launched the beta version of the Chrome browser for Linux. They provide RPM and Deb packages, allowing for easy installation.

Sometimes however, you're working on a Linux PC where you do not have root access. The following procedure allows you to install and run Chrome as a normal user:

• Download the .deb package and save it into your home directory
• Unpack it into a subdirectory called temp with the following command:

 $ dpkg -x google-chrome-beta_current_i386.deb temp

• Copy the Google Chrome directory to your home directory:

 $ cp -r opt ~

• To easily start up the app, create a launcher icon. Here is a good tutorial on adding a launcher to a panel. In the name field, type Chrome. In the command field, type /home/yourusername/opt/google/chrome/google-chrome. Click the icon, and go to opt/google/chrome to find the icons there.

2009-12-02 Who is logging in

Who is logging into my Linux workstation?

At my most regular workplace (I have several), I have a Debian Linux workstation. The username/password information is managed over NIS, and is configured such, that every user can log into every workstation.

I have no problem with this, but do like to know who is logging in when I'm using the desktop. Thus at startup, I run the following script in the background:

  #!/bin/sh

  [ ! -e /usr/bin/whoami ] && exit 1
  [ ! -e /usr/bin/gmessage ] && exit 1

  while [ 1 ]
  do
    LOGINNAME=`w  -h | cut -f1 -d' ' | grep -v whoami`
    if [ $LOGINNAME ]; then
      gmessage "User $LOGINNAME logged in" -button OK
    else
      sleep 1
    fi
  done

Save this script somewhere in your home directory. I've called it 'loginwatch'. Then make it executable and run it in the background as follows:

 $ chmod +x loginwatch
 $ ./loginwatch &

This script assumes that you use the Gnome desktop, because it uses the gmessage utility.

2009-10-19 Rolling back a change

Suppose you inadvertently made changes in some files some time back. You can examine revisions of files with

 $ svn log ccsds.h

You see that the previous revision was 205 and that it was correct. With an SVN merge, you can make that old revision the current revision:

 $ svn merge -r HEAD:205 ccsds.h

Check in your file and you're done!

2009-08-28 PHP client using Thrift

Today I was thinking about a PHP script that uses Thrift to retrieve a couple of results. We have the following Thrift definition:

 /* This contains the three things identifying a logging program */
 struct Logger {
     1:  string      userName,
     2:  string      hostName,
     3:  string      appName
 }

 /* This is a debug message */
 struct Message {
     1:  Logger      origin,
     2:  string      content
 }

 /* This defines the remote logging services */
 service RemoteLog {

     // send a log message to the logserver
     oneway void         newMessage      (1:Message aMessage)
    
     // get list of loggers available
     list<Logger>        getLoggers      ()
    
     // get messages from a specific logger
     list<Message>       getMessages     (1:Logger aLogger, 2:i32 aFromID, 3:i32 aMax)
 }

However, I'd then have to implement the reverse of the above description. In other words, I am asking the remote logging service for whatever he has received over time. To get this up and running, the following steps have to be taken:

1. Define Thrift definition
   
2. Generate PHP stubs (client side)
   
3. Rework these into script
   
4. Generate C++ stubs (server side)