These are some of the things I've done outside my main line of work or
studies, just for fun.
Computational physics and math
Particle collectives in arbitrary force fields
Take a force field with some arbitrary distribution (e.g. gravity
from a group of stars). Throw a collection of particles in it, with
initial positions and velocities. Calculate the trajectory for each
I used linear approximations of the field equations for very small
domains. The equations of motion were also linearized, iterating over a
very large number of very small steps. Therefore, any trajectory was
simulated as a succession of infinitesimal parabolic arches. It was
great to see the code converge to known analytical solutions (e.g. a
single particle around a single star would move on an ellipse).
Volume of simple bodies in N-dimensional space
In an N-dimensional space, consider an N-sphere circumscribed by an
N-cube. Calculate the ratio between the N-volume of the sphere and the
N-volume of the cube containing it, as a function of N.
I'm sure there's a nice analytical solution somewhere. But if
you're like me, you'll just do Monte Carlo with a
ton of samples, and derive an approximate result. As N tends to
infinity, the ratio tends to zero. That was very surprising.
1-bit ADC/DAC (analog-to-digital / digital-to-analog) converter
Take an analog signal (audio), convert it to digital via a 1-bit ADC
(actually, a delta modulator).
Send it via a single wire as a digital signal, convert it back to analog
via a DAC at the destination. I designed the ADC/DAC circuits from first
principles, based only on the theory of Delta modulation. Main design
constraints were simplicity and low cost.
The point was to show that a 1-bit digital line could carry sound
just as well as an 8-bit or 16-bit line, provided that the switching
frequency is high enough. It worked pretty well.
Wavetable synthesis sound card for 8-bit computers
An offshoot of a larger project (polyphonic digital synthesizer)
that never materialized fully. I designed and built the card from
scratch. RAM banks were used to store the waveform and the envelope, DAC
circuits and digitally controlled amplifiers instantiated the sound. I
wrote drivers for it in Z80 assembly, and then I wrote a software
synthesizer that could generate a variety of sounds.
For a high altitude balloon, collect data such as position,
altitude (via GPS), temperature, humidity (via appropriate sensors).
Record data locally to an SD card. Send data to ground station via APRS in the 144 MHz band. I've used an Arduino clone for
the microcontroller, and commonly available sensors. Ground tests went
fine. I've not launched the balloon yet, I'm waiting for a good deal on
Tachometer + fault protection
For the telescope mirror grinding machine, I've built a device that
can measure the rotation speed of the main rods, display it on an OLED
screen, and cut AC power to the motor when the rods get stuck. Again an
Arduino project, home-made tachometers, solid state relay on AC.
A small project for Halloween
using an ATmel AVR micro, coded directly in C.
A clock with a large LED display, mounted in the CD-ROM bay on a
PC. It's synchronized to the PC.
Romanian Linux Users Group
Founding member of RLUG (the Romanian
Linux Users Group). I was part of the small initial group who created
the organization. Educating the public at large, helping technicians,
engineers and administrators working in the industry, providing
resources (documentation, free software) and free support online -
these were our main focuses initially.
I believe we were very successful, locally, in helping the expansion
of free software in general, and Linux in particular, which became a
major component of the infrastructure in the region.
Computer technology summer camp
I led a small group of technology enthusiasts and local teachers
who organized a 1 week retreat, at a beautiful location out of town,
during the summer vacation, for students who were interested to learn
more about computers. We managed to pool resources, equipment and
services borrowed from or donated by local businesses, schools, the
Department of Telecommunications, and local authorities. The schedule
included classes on programming, networking, systems administration,
etc., but also unstructured time for kids to improvise, be creative,
and apply what they had learned.
The energy and enthusiasm were unbelievable. The kids learned a
lot, but I'm sure the adults did, too - whenever we could sneak into
someone else's class. This whole experience was its own reward. I would
do this again any time.
Science for kids
Literally a one-in-a-century event? Involving astronomy? Ocurring
in the middle of the day? Perfect as a science event for middle school
kids. It was the solar transit of
Venus in June 2012. The turnout was bigger than expected, as you
can see in this
Like this: https://plus.google.com/u/0/photos/...
Astronomy and optics
It turns out, making your own telescope mirror, starting with an
ordinary lump of glass, is not hard. It just takes a lot of
persistence. Here's the polishing and
figuring log for a mirror.
I made my own optical testing equipment (Foucault tester).
The telescope that uses that mirror can be seen at the very bottom
of that very long polishing log.
Specifically, its applications in computer vision.
...also known as "quadcopters" or "drones". Making progress
Basically a combination of the previous two items. I want to make a
drone that follows a red cue ball. Work in progress. Stay tuned.
Grinding / polishing machine for telescope mirrors
If you want to make very large mirrors, you can't grind and polish
by hand. You need a machine. Work in progress, as you can see in this video.
Very large telescope
I'm aiming for an aperture of 1 meter or larger. This will likely
require several successive steps, each one larger than the previous
one. I'll have to use FEM to design the
large but lightweight glass substrate; Elmer appears to
work well for this purpose and it's free.
Requirement: The viewport needs to be near ground level, which
means I'll have to use a different design (not newtonian); I have
several designs tested with OSLO that meet all
conditions, are diffraction-limited, and do not require grinding
impossible curves in glass.
This project is likely to take a long time, so do NOT stay tuned.