Older articles (2/18)

1. Creating a nomogram with Python and Postscript

   At work I needed a suitable way to check the calibration of gelcoat spray equipment. Gelcoat requires an initiator (often called “catalyst”) in the form of a peroxide to cure. The peroxide/gelcoat ratio is important, so it is checked regularly by spraying the separate components into suitable containers and weighing them.

   For those familiar with gelcoat spraying, this is not a system with coupled gelcoat and peroxide pumps. But rather an external mixing spray gun where the peroxide is simply fed from a pressurized container to the spray gun.

   Since we’re handling resins, solvents and peroxide, protective equipment including gloves is a must. That makes it cumbersome to whip out a smartphone to use it as a calculator to check the ratio. Since you don’t want to get gelcoat or peroxide on your expensive phone, you have to take off your gloves to handle it. This would have to be repeated several times.

   So I decided to make a diagram where one could relatively easy read off the peroxide percentage given the quantities of both components. This can be printed and laminated between plastic to make it resistant against stains.

   The whole thing can be found in a github repo.

2. Drawing with PostScript

   PostScript (in the form of ghostscript) was for me the first way to generate vector graphics outside of a CAD program. I have several hundreds of figures written in PostScript for inclusion in e.g. LaTeX document.

   Later I’ve started using other programs like metapost and asymptote. But in a sense, I’ve always been dissatisfied with them.

   When the book Mathematical Illustrations was mentioned on hacker news, this re-kindled my interest in PostScript. And I learned some valuable lessons from it.

3. TeXLive 2018 update

   Today I updated my TeXLive install to 2018. Although the install went fine, there was a problem with the binaries.

   Both asymptote and xetex were linked to different versions of some libraries than those that are supplied by ports. So I had to rebuild them.

4. Using the FT232 with Python

   In this article I will try to document how to with with the FT232H using Python on FreeBSD. I will be using the Adafruit FT232H breakout board.

   Note that since I’m using FreeBSD, the library provided by FTDI doesn’t work. However, the library provided by Adafruit was written for Python 2, and doesn’t work with Python 3. I tried tinkering with it a bit to get it to work with Python 3, but that did not work out. In the end, I went with pyftdi since it doesn’t require a native library and it just works.

5. Measuring particulate matter with the PMS5003

   This article details how I used the Plantower PMS5003 particulate matter (“PM”) sensor on a PC or laptop, using an FT232H breakout board to make the connection.

6. Storing and graphing time-based data

   In this article we will look into the best way to store time-based data and use it with gnuplot.

7. Yes, please: #DeleteFacebook. But don’t leave it at that.

   Cut facebook out of your life altogether.

8. Video manipulation with ffmpeg

   Serveral useful recipes for manipulation video with ffmpeg.

9. Adding an overlay to each page of a pdf file

   We can use PostScript’s Endpage procedure to e.g. add a signature to each page of a PDF file, using only ghostscript.

10. Install ntpsec on FreeBSD

    A short article on how to install ntpsec on FreeBSD. Tested with 0.9.7 and 1.0.0.

    Note

    There is/was a bug in the ntpdate implementation that set the clock to a completely bogus value. So I’ve since written a simple script that runs from cron to fetch the time from a near NTP server.