Computer keyboards are peripherals partially modeled after the typewriter and designed both for the input of text and characters and also to control the operation of a computer. Keyboards can arrive in many shapes or sizes. 14 Cool Computer Keyboards for Geeks shows you a set of extraordinary and interesting computer keyboard designs currently available in the market.
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Cool Computer Keyboards
Monday, December 21st, 2009How an expensive Blue-Ray player is made
Friday, December 11th, 2009AV Science Forum has an interesting posting on Ayre DX-5 blueray player. The article claims that Ayre DX-5 bluray player is a modified Oppo BDP-83 blueray player and even describes the modifications made to the device. Interesting article indeed to read, although I am a pretty skeptic would those modifications be worth of all of the money they cost (from $500 to $10000). Maybe for someone, or maybe not…
Some picks from article:
“Well, first of all you have to remember that we don’t have to pay $500 for the unit.”
“Then to make it an Ayre, we dismantle it completely and recycle everything except the main PCB (with the video decoder, ABT scaler chip, and HDMI transmitter), the transport mechanism, the VFD display, and the remote control handset.”
“All of the supplies are replaced with pure linear supplies with analog regulators.”
“Next, we replace the low-quality master video clock with a VCXO.”
End comment: “If you want a great Blu-Ray player for an incredible price, buy the Oppo. If you want the best picture and sound quality in the world for your home theater and price is not a concern, check out the Ayre. And no, it will not be available in November, sorry. Early next year will be a better guess.”
Another article on the same topic is Ayre DX-5 at $10,000 is a rebadged $500 OPPO.
Build a Mechanical Computer
Monday, November 30th, 2009Build Your Own Digicomp Mechanical Computer! tells about a plastic mechanical computer from the 1960s. It offered three bits of tabletop computing, back in an age where corded telephones were considered high-tech. According the article Digicomp started a bunch of kids on a career in computers. Now a member of “Friends of Digicomp” Yahoo Group has introduced an updated version this cool little looking machine. This kind gadgets have potential to give combination of hands-on and minds-on fun.
Nokia N900
Monday, October 5th, 2009I had yesterday change to play a little bit with Nokia N900 mobile communicator at at Expert Expo in Helsinki. This brand new Nokia smartphone that you can’t yet buy anywhere, just pre-order. This device runs on Maemo Linux operating system and worked well. This device felt much better than Nokia N97. The tough screen seemed to work better and overall feeling was that the system was considerably more responsive. Linux will rock on mobile devices. There was even a X Terminal on that device available, so Linux hacker can do different things on traditional command line.
Digital audio isolation
Friday, October 2nd, 2009Isolator for digital audio is needed in cases where coaxial S/PDIF digital audio link forms a ground loop in your audio system. Typically in coaxial S/PDIF connections the coaxial cable shield is connected to equipment cases. This arrangement easily creates ground loops which can cause noise problems in various places in audio system. A suitable transformer can be used to isolate the coaxial S/PDIF signal and avoid ground loop problems (other option is to use optical connection instead of coax). Here is the circuit of the S/PDIF signal isolator I have used:
ELFA catalogue product 56-550-55 “PE65612 Trafo dig.siirt.” is a tranformer suitable for isolating S/PDIF digital audio signal. The manufacturer for this product is Pulse Engineering and their product code is PE-65612.
Ratio: 1:1
Bandwidth: 100 kHz-55 MHz ±3 dB
Here is a picture of the S/PDIF signal isoltor I built (box open):
More information on S/PDIF and related circuits can be found on my SPDIF document.
Build a Ground Loop Detector
Thursday, September 24th, 2009Ground loops are a common problem in many experimental setups. A ground loop is an un-
wanted closed loop of cables in the setup, most often through the ground system. Those ground loops are often hard to find and debug. A Ground Loop Detector document describes how to build and test a simple system to detect ground loops in experimental setups. The two circuits used are from article “Simple system for locating ground loops” by P. M. Bellan. The ideas used on those articles are used in commercial product Loop Slooth. The idea in those circuits is to induce the test signal (100 kHz) into the ground system and then detect the amplitude of that signal in different parts of the setup with help of Rogowski coil based detector circuit. The basic idea in this circuit looks very promising. I have not yet tested the presented circuits, but at some laboratory tests the basic idea behind this circuit seems to work.
Troubleshoot ground loops with clamp multimeter
Monday, September 21st, 2009A normal way to troubleshoot ground loops problems in audio systems is to listen to the audio signal at the mixer with headphones. If the buzz exists at the mixer then do the following: One by one, disconnect the inputs and outputs to and from the mixer and note if the buzz decreases. This same connecting and disconnecting wires method can be used on other components of audio and video systems.
Disconnecting and then reconnecting the cables take a lot of work. This caused that ground loops are frustrating to troubleshoot in large systems where there are lots of cables.
I have found that a clamp type multimeter can help to troubleshoot ground loop problems. The ground loop noise is normally caused by the extra noise current flowing on the shields and ground wires of the cables. That noise current is normally mains voltage frequency (50 Hz / 60Hz) or it’s harmonics. Normally the signal cables should not carry any (or very little) mains frequency current in them, so by measuring this kind of current flowing on the cable it is possible to determine where the noise current flows. A clamp type multimeter is a very good tool for doing the measurements, because you can easily measure the noise current flowing on the cable with it without need to disconnect the cable or disturb the signal inside the cable. This means that you can troubleshoot a live system with clamp multimeter in AC range.
The wires which have considerable current on them are part of ground loop. The wires with most current on them are pushing most noise current to the whole system. So first locate the wires that have highest or otherwise very high current flowing in them. Then you can try to disconnect them and test if that stops the noise. Usually there is one or few cables that cause all or most ground loop current on the system. That noise current gets typically flowing around in different cables on the system, causing more or less noise problem here and there around the system. Then the real noise source or sources are disconnected, suddenly the whole system becomes noise free. When you have found out the problem source then just add suitable cure to that connection (typically signal isolation transformer or similar device).
Clamp on multimeter allows you to easily measure the current on cables. Just clamp the meter over the audio cable and get the AC current reading. If you want you can clamp several audio/video cables inside the clamp and get the reading of the sum of their noise currents (remember that there is possibility that if there are two cables with exactly same noise signal but different direction you get zero reading). Clamping the meter around a number of signal cables speeds up the troubleshooting process where there are lots of cables, for example near audio mixer. If the group of cables you measured with clamp meter shows a considerable noise current, then measure the cables individually to see which one has the most current flowing. If there was no considerable current on the cable group, continue measuring next cable group. Besides audio cables you can do the measurement with video cables, mains power cables and other signal cables.
There are few things to consider the selection of the clamp type multimeter. First the multimeter needs to measure the AC currents with the clamp. You don’t need the DC current measuring capability, although getting a clamp meter with also DC capability can make the meter more useful for other applications (usually the DC capable clamp meters are more expensive than AC only). The second thing to consider is the resolution of the meter. The ground loop currents you normally want to measure are in few mA to 1A range (in some severe case the current can be considerably more). It is preferred to have a clamp meter that can measure currents down to few mA. Unfortunately many meters with this good resolution are usually quite expensive.
Usually the cheap clamp type multimeters have 10 mA or 100 mA resolution, meaning that they can’t detect anything lower than 10 mA or 100 mA. A multimeter with 100 mA resolution is practically useless in ground loop problem solving, because over 100 mA ground loop current are not seen often. A multimeter with 10 mA resolution is already useful to troubleshoot ground loop problems, but it will not reveal you all the details in most cases. Usually 100 mA-1A current on cable means very serious noise problem on audio and video systems, currents in 10-100 mA range cause some noise problems. Usually when the current is well below 10 mA there are no considerable noise problems.
I have used a clamp meter with 10 mA successfully for troubleshooting ground loop problems, but when used that I wished I had a meter that can show even lower currents down to 1 mA or less. So if you are buying a clamp meter, consider trying to get as good resolution as possible with the money you are willing to spend it. When looking for multimeter for this application the actual measuring accuracy (measurement error percents promised) is not important, we are merely making checks if there is current flowing or not and approximately how much (just some approximation around how much current is enough).
This picture shows the cheapest I know well working clamp multimeter that can measure currents AC down to few mA currents. The meter has 1 mA resolution at 2A measurement range (the display started showing current higher than 2 mA). You can get this 1.3″ LCD Clamp Style Digital Multimeter with Pouch from Dealextreme for around 20 US dollars.
Build video isolator
Tuesday, September 15th, 2009Video isolation transformers are primarily used in CCTV application in fields of security, manufacturing, avionics and display. The video isolation transformer is an extremely broad bandpass 1:1 isolation transformer. Its hum isolation is very good and it can sustain very high noise voltages without degradation. Isolation decreases with increasing noise frequency.
Video signals can transformer isolated in many applications. Most video signal transport paths are AC coupled, so this kind of signal can pass through a suitable transformer. Video isolation transformers are used CCTV applications where they solve ground loop problems or protect system against ground potential differences between different locations.
The design of a high bandwidth transformer which can go to very low and very frequencies is very hard. Video signal can have significant signal components from 50 Hz up to 6 MHz. Unfortunately in practical transformers you have to always make some compromises on low and high frequency responses (highest components of composite video can be attenuated even few dB). Signal amplitude at low frequencies is limited by core saturation and coil inductance. High frequency response is limited by leakage inductance and winding capacitance. Many video isolation transformers are only designed for CCTV other not so demanding applications application, where more signal distortion is accepted than in broadcast industry.
Lundahl LL1575 is a high bandwidth video isolation transformer designed for CCTV (closed circuit television) applications. I have used that transformer successfull to build video video isolators. That transformer has 20 Hz – 11 MHz +0 /- 3 dB frequency response (possible with special bifilar winding technique and special core construction). That transformer gives 2 kV rms isolation between primary and secondary windings.
The LL1575 datasheet recommends that if DC current is present, the transformer must be decoupled (with large capacitor). Because in many video circuits there can some DC present especially in video outputs, I thought that it would be a good idea to include suitable DC blocking capacitor to the circuit input side (on the left, connected to video signal source output). A suitable capacitor value should be 1000 uF or higher (practically demands using electrolytic capacitor) and have good high frequency characteristics (electrolytic capacitors are not good at this, ceramic etc.. would be much better here). The capacitor I used was built from 4700 uF electrolytic capacitor (gives capacitance) wired in parallel with 100 nF ceramic capacitor (handles the high frequencies where electrolytic capacitor is not good at). 25V or higher voltage rating is suitable for the application (you normally see 1Vpp video signal plus maybe few volts DC).
The circuit is best constructed to a small plastic box with suitable connectors. For professional applications I recommend to use BNC connectors. If all your equipment use RCA for video signal, then use those connectors if they are easier for you. Plastic box is easiest for the construction because in this way it is easy to guarantee good electrical isolation between input and output side connectors (in metal box needed isolation could be hard to do reliably).
Here ia picture of the video isolator I have built:
See inside PC parts
Monday, August 31st, 2009You may know what the inside of a PC looks like, but what about the parts which make up your PC components? Your Hardware Exposed! 22 PC Parts Bare All article has pictures what is inside hard drives, keyboards, soundcards, and a plethora of other PC hardware. Just to see what makes them tick.
Router speed control to light dimmer
Tuesday, August 25th, 2009More than a year ago I was approached by an independent filmmaker about light dimmers. The problem fo them was how to get affordable light dimmers to control the film lighting. I was told that many independent non-commmercial filmmakers use a HarborFreight router speed control to dim the lights used for moviemaking. The reason is that they are are cheaper and far heavier (15A) than building our own from a 600W house lights dimmer. The problem with these router speed control devices is that they do not dim down enough to turn the lights off. They also don’t quite go to full brightness but that is a minor problem as they have a switch that bypasses the electronics and provides full power.
After some discussion I got one of these units mailed to me to see if there is a way to modify those to work as better light dimmer.First thing I did was to open the device to see how it was built out. Based on what I saw the circuit was pretty close to a traditional light dimmer. And there seemed to be also some adjustment trimmer for some adjustments. Looked promising.
The nest task was to test the device. The problem that those are designed to operate 110-120V AC 60 Hz power has a slight problem to me. In Finland the mains power is 230V AC 50 Hz. Getting real 120V 60Hz power and finding 120V AC light bulbs is hard here where I live. I got one 120V lamp with the router speed control device so I had suitable lamp. Getting real 60 Hz power would involve some expensive power converter or using 12V to 120V AC true sinewave inverter or something similar that I did not have at the moment. So I decided to do my first testing with 110V 50Hz power that I get easily with a suitable voltage conversion transformer (I used fully isolating transformer for safety).
I did some testing. I found that the controller trimmer potentiometer controls how dim the output can go. I was able to get lamp very dim. Here is the picture of the dimmer electronics with a well insulated screwdriver adjusting the trimmer (there is a hole on the circuit board that gives access to the trimmer). Well insulated screwdriver and isolation transformer powering the whole circuit makes it possible to do ajustments with live circuit pretty safely when you know what you are doing. I mailed the results back to person who sent me the router speed control and he tested the results with real 60 Hz power (they worked).
The adjustment instructions: Set the potentiometer lowest setting. Then adjust the trimmer so that you get as dim light as possible without noticeable side effects. When you set the trimmer to too low setting, turning potentiometer will cause the output to be completely off (lap turns off). When dimmer reaches this full iff state, the dimmer potentiometer need to be turned quite much (one third or one fouth) until the light turns back on, quite bright already. The ideal setting I think would be that the lowest dimmer potentimeter setting would just set the bulb to be just barely on (lamp filament dark red and does not make much light), so you have always full control range from it to full setting without problems.
In this way a relatively cheap router speed control device is converted to a relatively inexpensive high power light dimmer.
