Few words about me:From very childhood I loved computers, electronics, lasers, sulfuric acid and liquid nitrogen. I always wanted to be making microchips, UAVs and see nuclear explosion.
Now I am doing software engineering and in the spare time - some microelectronics and physics/chemistry experiments.
I live and work in Russia, Moscow.
My HeNe lasers and DIY ballast resistorRecently I won HeNe laser tube on EBay, and seller from Germany surprisingly sent me 2 lasers instead of 1 :-) One is slightly newer (~2000), I even managed to find datasheet on manufacturer's website, another is older. Also I bought HV power supply - 2100-2900V, 6.5mA and 8000V during ignition. But the main issue for me was high-voltage ballast resistor - it is needed to stabilise "negative resistance" gas dischange, as constant current power supply might not react fast enough. They are typically large, super-insulated, wire-wound, expensive and hard to find. I decided to try to make it by myself using 2512-size SMD resistors.
Voltage drop across 200 kOhm resistor for 3mA current is about 600V, so it did not brake down even for mere 2 resistors in series, but heat dissipation was so high that resistors were floating in molten solder. Obviously, It was impossible to add radiator on my protoboard I increased number of resistors to 6 and reduced total resistance down to 150 kOhm - this allowed for prolonged laser operation without resistor overheating. Now I see that i probably used too high ballast resistor value - even 75kOhm would work just fine according to datasheet. FYI documentation also suggest to place ballast resistor as close as possible to anode of the laser for stable operation.
I believe ballast resistors for CO2 lasers could be done the same way - but number of resistors must be like 10-30 times higher, and obviously on a single-sided board. One should remember that maximum heat dissipation for 2512 resistors is around 1W and temperature of whole ballast board should be monitored.
First laser started generating from 3.2mA (nominal current from datasheet - 6.5mA), second from ~4mA. I was measuring current using usual multimeter in the cathode wire - luckily it did not get fried during ignition
FTDI FT232RL: real vs fakeFor quite some time when you buy FTDI FT232RL chips from shady suppliers you have a good chance of getting mysteriously buggy chip which only works with drivers 2.08.14 or earlier. We've got a pair of such FTDI FT232RL chips - one genuine and one fake and decided to check if there is an internal difference between them. On the following photo - left one is genuine, right one is fake. One can notice difference in marking - on genuine chip it's laser engraved while on buggy it is printed (although this is not a universal distinguishing factor for other chips).
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February 19, 2014
Precision clock: rubidium atomic clock and Russian DOCXORecently I bought on ebay rubidium atomic reference clock for my precision time experimets (time drift per year under 50ms) and also double-ovenized 10Mhz quartz cristal oscillator from the same supplier (just for comparison, it was cheap as dirt).
After I received them - was really surpried that DOCXO is made in Russia, Saint Petersburg by Morion company. So this DOCXO made a full trip around the world - from Russia to China and back
February 5, 2014
Supernova explosion in M82 galaxyJust made a photo of supernova in M82 galaxy which exploded yesterday*. If things would go well, it will be getting brighter and brighter in the following 10 days or so.
0.5m telescope aperture with 3 minutes exposure:
▶ And this is how it looked before explosion:
January 23, 2014
M1 - Crab NebulaMade a photo of Crab Nebula via "couch telescope" iTelescope T7.
10 minutes for each channel, Ha (red channel), Sii (blue), Oiii (green). I.e. different colors - are different chemical elements (hydrogen, sulfur, oxygen) generated during nova explosion. We are looking here at the process of creation of the new world :–)
BTW Explosion of this nova was first observed just 959 years ago. It is even possible to see changes in Crab Nebula over the years.
Same without filters:
November 23, 2013
CD & DVD under microscopeI knew that there are tracks, but never was able to see them. My old pocket microscope was too weak.
Update: Photos remade with new camera. Also figured out how to make a good photo of DVD - I needed to brutally crack disk at half of it's thickness to directly access surface with written data.
Track interval is 1.6µm for CD and 0.74µm for DVD.
Photo of AMOLED display of Galaxy S4 mini and othersUpdate: Just realized that AMOLED means Active Matrix, so there should be transistors and some circuitry which I need to take a look at!
Suddenly my HTC One V died - blinked some random garbage on screen and became dark, discharging battery below 0%. I am not going to buy HTC again - I am far from happy with their policy of not updating Android on their 'small' phones.
As I am cool enough to buy non-top-of-the-line phones, I gone for Samsung Galaxy S4 mini. Why on earth all manufacturers have so much love for gigantic phones...
S4 mini has my beloved AMOLED display which promises longer battery life, 1.5Gb of ram is more than enough, 28nm Krait CPU (1.7Ghz, 1Mb of L2 cache) is perceivably faster than Scorpion (MSM8255 - 1.4Ghz, 45nm, 384kb L2 cache) and playing with NFC is fun. Finally it has LTE support - we already have LTE-capable networks here in Moscow - will be interesting to test it out. Also GLONASS is working
I decided to take microscope photos of displays of various devices I had at hands. Scale is the same on all photos:
Samsung Galaxy S4 mini - AMOLED: