HDR Images of my Workplace

When I went home tonight, shortly after 10 pm, I noticed the wonderful light around the institute where I work. So I quickly got my camera and took some high dynamic range images (HDR). They are created from several 5-image-series with 2 stops spacing between them (-4 EV to 4 EV). For the HDR process I use the affordable easyHDR Pro software (around 30 EUR) with its “Smart Merge” function. This leads to images that have an increased dynamic range but lack the typical HDR artifacts like color fringing and noise problems, as the best parts of each image are merged and not all the image. It’s also faster than a real HDR calculation. The resulting images are slightly tonemapped, but I tried not to overdo it.

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Tuesday, July 14th, 2009 General, Photography, Science No Comments

Building a DIY LED from SiC

Wohoo, that are many abbreviations in the title. What this article is about is making a light emitting diode (LED) from a pin and the mineral Moissanite. Moissanite is Silicon Carbide or Carborundum (compound of Silicon and Carbon- SiC) and since it is such a rare substance I used a synthetic form of it. Most of you will know this substance as the black “sand” splinters on sand paper. Due to its extreme hardness it is most often used in abrasive substances and tools. You could easily cut glass with it. I picked up four boxes with 1 cm big crystals for one Euro total on Ebay.

Box of silicon carbide crystals.
Single crystals and pliers as size comparison.

That this material- besides its strength- has another impressive property was discovered by H.J. Round, an american radio engineer in 1907. While experimenting with it as a diode substance in a radio transmitter, he noticed a glow at the contact point of a wire and the silicon carbid. This was the first “LED” known to man. While Round only published a short note on it, a russian physicist named Oleg Losev properly described the properties of this phenomenon and is credited as the inventor of the LED.  While reading his biography I stumbled  upon an article in Nature:Photonics, where the history of the LED is “illuminated”. This got me to try to build an LED myself.

The setup is very simple. I took a crystal of SiC and attached a clamp to it to supply it with about 20 Volts. It is important that the plus clamp is used. It is further advisable to limit the current to something around 30 mA. This will prevent the crystal from heating up too much, as the diode forward voltage will be only on the order of 9 Volts @ 30 mA. If you have no current limiter on your power supply or want to use a battery, use 12 Volts as fixed voltage and be careful not to overheat your setup. The negative lead is attached to a wire which holds a regular pin from your sowing supplies. After applying the voltage the pin should be moved across the surface forming a cat’s whisker detector. Every now and then a tiny light appears at the contact point. This is the LED! Depending on the site and the current flowing it can be orange, yellow or green and can potentially be relatively bright. To find a perfect spot is however difficult. If you want to replicate the experiment and don’t see a thing, check whether the room is dark enough, the polarity of the leads, the voltage and- if nothing helps- use the side of the needle and trace the edge of the crystal. The current will be higher and so will be the chance of finding a good spot. I also found cracks in larger crystal surfaces to be rewarding. Here are two pictures of the whole thing:

Setup of a home made cat’s whisker detector from SiC and a pin.
The green glow of the DIY LED! At the contact point of pin and crystal greenish light is emitted.

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Thursday, May 7th, 2009 Electronics, Science 5 Comments

Welcome to my site!

I am a graduate student at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany. My work focuses mainly on the integration of different senses in the brain and its underlying neural activity. The techniques I am using are electrophysiological recordings, functional magnetic resonance imaging (fMRI), voltage-sensitive dye imaging (VSD) as well as microscopy. For my publications please see the publication list on the sub-page “Me” (soon).

On my site I would like to give you an overview on what I do and what I find interesting. The Electronics section has some electronic circuit ideas and the Microscopy seciton features some of my microscopic images. Photography should be a pretty self-explanatory category.

Due to the fact that I finished my masters thesis only recently, this site is not yet complete! Please come back in the near future, there will be more online soon.

Thursday, March 5th, 2009 Science No Comments