The theremin is an early electronic musical instrument controlled without contact from the player. It is named after its Russian inventor, Professor Léon Theremin, who patented the device in 1928. Theremins are distinguished by the fact that they are played without the performer touching the instrument. The musician moves his or her hands in proximity to the theremin to control the tone of the sound. I was told that mastering the theremin requires skills and lots of practicing, but only a few instrument provide the unique visual appearance of performance. The sound is quite unique for that instrument. Even if you don’t know theremin by name, you might have heard the sound of it at The beach boys -good vibrations or on the sound offects of some old scifi/horror movies.

The electronics of the theremin consists of two high frequency oscillators connected to antennas. When the player moves hand near the antenna, that changes the frequency of the oscillators, and that changes the sound (frequency or amplitude depending on antenna). Here is a block diagram of theremin from www.thereminworld.com Fred Tells All article.

All DIY persons now interested in theremin instruments can also view Make a Theremin video and check ePanorama.net theremin links.

Image source: http://blog.8thlight.com/articles/2010/2/25/walk-and-code

Earlier some hifi people have built hi-fi stand made out of IKEA Lack side tables, but now the world is ready for 19″ networking equipment racks. Check LackRack home page for more information on how to build your own very cheap 19″ rack system. The page also tells that also Ikea LACK coffee table and Ikea ODDA night table have right dimensions and can be easily converted to cheap 19″ racks.

Image source: http://wiki.eth-0.nl/index.php/LackRack

I tested the circuit idea with a slightly different setup and it worked well. I just picked a random small stepper motor I had lying around. It had around 90 ohm coil resistance. I used a 10 uF capacitor (a small electrolytic, dry capacitor would be better for long run). The power source I used was 24V 50Hz AC. The stepper motor run with the circuit nicely at least the short time I tried it. I did not run it for a long time because I did not know the specifications of the stepper motor, and I feared that the 24V AC could be too high for it (could cause overheating on long run).

On the same web page there is also another circuit for powering electret microphones is by means of “T-power”.

You can find more information on microphone powering at my document Powering microphones.

A lot of “bad” fibers can be traced back to dirty connectors. You can see the dirt with microscope. But usually it is always easiest just to clean the connector every time you suspect it could be dirty. So always clean the fiber before plugging it into an interface. Cisco document Inspection and Cleaning Procedures for Fiber-Optic Connections gives you a lot of information on fiber connector cleaning.

WARNING: Remember to check that no power is present in the cable before you look at it in a microscope ­ to protect your eyes! The microscope will concentrate any power in the fiber and focus it into your eye with potentially hazardous results. Some commercial fiver microscopes have laser safety filter in them but this DIY model does not have it.

Attach the light source a fiber optic cable to test to the visual tracer and look at the other end to see the light transmitted through the core of the fiber. If there is no light at the end, go back to intermediate connections to find the bad section of the cable. Warning: Avoid looking at other fibers that could have signal in them, because active communications fibers can have so much invisible laser power in them that it can damage your eyes!

EDN design idea LED flasher checks fiber-optic strands allows you to verify fiber-optic strands. It uses two high-intensity flashing LEDs (red and yellow) that you can see at the far end of multi-mode fiber link (up to 1 km). Basically the circuit is LED flasher with some extra features (like auto power-off after 50 minutes). The fiber transmitter module is constructed simply: the T1-3/4 LEDs fit nicely into ST barrel connectors with some glue to hold them in place. If you need some other fiber connector type, you can use a patch cable to match the fiber connectors in your network.

Nice circuit idea but the circuit looks a little complicated for a LED flasher (three ICs). If you want to make something simpler, I think that you could also try the same idea with just one simple 555 timer based or other simple LED flasher circuit.

It is even possible to use a flash light for this application with suitable adapter or you can make your own light source if the commercial devices look too expensive. I own an a simple plastic adapter that connects a Mini Maglite to many common types of fiber optic connectors. It is an Universal adaptor for connectors with 2.5mm ferrules (works with FC/SC/ST connectors). It was given out for free at some fiber optics fair years ago and made from cheap plastic. It is not ideal, but it works and does the job many times.

There are also higher power versions of such tracers. A higher power version of the tracer uses red laser light that is powerful enough (typically few mW) to show breaks in fibers or high loss connectors. You can actually see the loss of the bright red light even through many yellow or orange simplex cable jackets. The red laser light can also be seen from the other end of the fiber cable that can be many kilometers long (ranges typically of up to 5km). This kind of gadget can be also used to optimize mechanical splices or pre-polished-splice type fiber optic connectors. Laser pointers are really cheap nowadays, but it is a bit hard to focus the laser beam from them well to the thin fiber.

Invisible infrared radiation normally carried in optical fiber can be made visible with a video camera. Many video cameras will detect IR radiation quite well, both black&white and color cameras (usually as RED but can be other color as well). The camera on your cell-phone can also usually work as a really cheap “laser” detector that nearly every tech carries. For example N73 cellular phone camera showed 1300 nm light as weak blue color on the fiber that has the signal in it. Because I can see IR remote control signals (850 – 950nm) on cellular phone camera, should 850 nm IR signals from fiber show as well.

The primary tools for serious fiber optics testing are a fiberscope for visual connector inspection and a power meter with laser source, a set of laser goggles (if you plan to work on single-mode or long-haul multimode fiber), an assortment of fiber patch cables, and a mini-maglite with fiber adapter (for simple continuity tests). There are many tutorials on the web showing how to use these tools, most from equipment vendors themselves, and some are even high quality video presentations.

More fiber optic testing ideas and information can be found at Fiber Optic Testing FAQ, LANshack.com Fiber Optic Testing, FOA Reference Guide To Fiber Optics Fiber Optic Testing, Measuring Power in Fiber Optics and Can You Build a Fiber Test Kit On a Budget?

Here is picture of most common fiber optic connector types (from Asara web site): LC, MU, MT-RJ, SC, ST and FC

LED lights are becoming more and more popular for common in Christmas lights for many good reasons. They consume considerably less energy than traditional light bulbs and fail much less often. If you LED lights fail, you can find ideas how to fix then at LED Christmas Lights and How to Fix Them web page.