Friday, August 18, 2017

Building wsjt-x 1.8rc1 on Fedora 26

The available binaries of wsjt-x don't run on Fedora 26. There's no problem building but it took a while to figure out the dependencies so this post is a note for myself that might help someone else.

From a fresh Fedora 26, here's the dependencies I needed to add before building.

sudo dnf install autoconf automake libtool libusb libusb-devel fftw-libs-single fftw-devel texinfo qt5 cmake asciidoc gcc-gfortran gcc-c++ qwt5-qt4 qwt qwt-qt5-devel qwt-qt5 qt5-qtmultimedia qt5-qtmultimedia-devel asciidoctor qt5-qtserialport qt5-qtserialport-devel

I stumbled around a bit figuring out what the missing thing was called in Fedora so there's undoubtedly things in that list that aren't actually needed.

At the end of the build I got an error linking -ludev so needed to do this to let ld find the library.

sudo ln -s /usr/lib64/ /usr/lib64/

(Let me know if there's a correct way to do this, I couldn't find a -devel package that should normally do this).

I basically follow the instructions directly from the excellent INSTALL document but I'm substituting the 1.8rc1 tag so I get the latest FT8 stuff.

cd ~
mkdir wsjtx-prefix
cd wsjtx-prefix

Download a snapshot from:

Unzip then rename:
mv wsjt-wsjt-8028-tags-wsjtx-1.8.0-rc1 src

From the file src/INSTALL, follow the instructions to download, build and install hamlib.

# As per the instructions in INSTALL
cd ~/wsjtx-prefix
mkdir build
cd build
cmake -D CMAKE_PREFIX_PATH=~/hamlib-prefix ../src
cmake --build .
sudo cmake --build . --target install


Building is a good way to exercise your CPU.


I notice this site hopes to have binaries available but the builds seem to be failing. Does anyone know what I need to do to build wsjt-x as a static binary for easy distribution?

Sunday, August 13, 2017

Charging a laptop from 12V

Keen on portable QRP operation, I'd like to use digital modes which might require a laptop. While battery life is excellent with some models, I'd also like to be able to charge a laptop from my solar powered shed.

Recently I purchased some voltage buck modules which can step up a voltage to a settable output controlled with a multi-turn potentiometer.

There's lots of variations of these on ebay. This one takes an input of 3-35V DC and turns it in to an output of 2.2-30V DC with an output current of up to 1.5A.

I'm charging a little HP laptop which takes 19.5V so the converter is set to that and all boxed up nicely. (Except that I drilled the holes in the wrong places).

HP laptop chargers have three wires in the lead, positive, earth and ID. The ID wire (I learned thanks to commenter Brian G8OSN) needs to be pulled high for the laptop to charge the battery. I connected the middle ID wire to positive 19.5V via a 100K resister and that seems to do the trick.

On a related topic, I'm becoming a fan of 18650 Lithium Iron batteries, not just for super bright torches and Tecsun radios, but also for powering QRP gear if powered from a set of three 3.7V cells in a little case available for under $2.

These cells can be harvested from old laptop battery packs. Often when they die it's because one cell has gone bad and the others can be re-used. They don't make it easy to get them out though.

This pack from an old Asus netbook has three rows of two cells in parallel. These cells have a huge capacity compared to an AA rechargeable which might be 1,200mAHr, they are often 5,000mAHr or more. Here they are in the fancy new charger that's just arrived.

I see that this month's Silicon Chip has an article about these cells.