Archive for July, 2009

Floating measurements

Friday, July 31st, 2009

A floating measurement reads the voltage between two points, neither of which is at ground potential. A most typical floating measurement done quite often is when doing voltage measurements with a battery powered multimeter. The floating insulated multimeter allows doing floating measurements of slowly changing signals easily.

The advent of switching power supplies and motor controllers brought a need to characterize waveshapes, timing, distortion, and other dynamics. Today’s power measurements call for an oscilloscope. Floating measurements of fast AC signals are a challenge for conventional instruments. The traditional line-powered benchtop oscilloscope models typically lack the possibility of making floating measurements. There are many compact battery-powered scopes around, but many of them have inadequate bandwidth and sample rate for accurate high-frequency waveform capture. Floating measurements have unique requirements over and above the usual considerations of bandwidth and resolution. Foremost among these issues is operator safety.

The Three Facets of “Floating” Measurement Solutions document at Tektronix web site examines the available alternatives for measuring AC signals in an ungrounded environment. It will show how the balance between three characteristics ­ safety, packaging, and performance ­ determine an instrument’s effectiveness for making floating measurements.

safety_fig1

Posted in Uncategorized | 2 Comments »

Syncing Music and Fireworks

Tuesday, July 28th, 2009

Design News has published an interesitng on-line article
Gadget Freak Case #128: Syncing Music and Fireworks on how Deane Williams fixed up his PC to synchronize fireworks with music. He used his PC’s parallel printer port to connect the circuit controlling the fireworks. The software was written in Agilent VEE 8.0 but Williams says it could have been written easily in Visual Basic 6 or any similar language that can use ActiveX calls. There is a video available how it work. More details including circuit diagrams is available in Word document format.

fireworks-blue

Posted in Computers, Entertainment Technology, diy | 4 Comments »

Ethernet history

Monday, July 27th, 2009

In 1973, Bob Metcalfe sent an internal memo to his colleagues at Xerox proposing a local system of interacting workstations, files, and printers. The devices would all be linked by one coaxial cable, he said, and would run within a local area network. He called the system an Ether Network, or Ethernet. And 36 years later Ethernet is going on strong, although the technology has changed more than a bit on the way. In this original vision, there was no need for hubs. Somehow once everything became balanced twisted pairs the “ether” became segmented into little mini-ethers held back from each other by digital logic.

Photo and original diagram of the world’s first ethernet cable web page has a nice picure of the first Ethernet cable installation and first drawings of Ethernet vision.

first ethernet cable

Posted in Computers, Telecom and Networking | 12 Comments »

MOSFET testing

Saturday, July 25th, 2009

Multimeters are very good tools to find out problems in electronics circuits and testing electronics components. Resistor measurement is found in practically all multimeters, capacitance measurement range is becoming more and more common and some high-end models can also measure inductance. Many multimeters have also possiblity to test bipolar transistors (Hfe measurement range), but I don’t remeber that I would have seen any multimeter that has measuring range for FET testing.  Properly testing all properties of a MOSFET requires a lot of expensive test gear. What would be useful is a way to easily have a working or not working result with some simple test that can be made with a normal multimeter and maybe few other components.

MOSFET TESTING page published by Integrated Publishing gives you idea how to test P-channel FET, N-channel FET and MOSFET with a multimeter. Testing a MOSFET web page gives you a simple testing procedure is for use with a digital multimeter. For the provedure to work you need a digital multimeter in the diode test-range with a minimum of 3.3 volt over d.u.t. (diode-under-test). If your multi-meter is less than that it will not do the test. 4QD Tec MOSFET testing page starts by giving a pretty similar test procedure, but continues with an improved test setup that need few extra components.

Please note that MOSFETs are very sensitive to electrostatic charges and can be easily damaged by them. A vacuum plunger (solder sucker) must not be used because of the high electrostatic charges it can generate. Solder removal by wicking or using professional ESD safe tools is recommended. It is also good practice to wrap MOSFETs in metal foil when they are out of a circuit.

mostest

Posted in Electronics Design, diy | 1 Comment »

Controlling dangerous things safely

Saturday, July 25th, 2009

Fire When Ready – A Pyro-Electric Safety Primer is a great document on issues around controlling dangerous things electrically. The document tells the techniques used on pyro/fireworks electrical control. Quite similar practices are used in other control applications where potentially dangerous things are controlled using electrical circuits or electronics.

Posted in Electronics Design, Entertainment Technology | 4 Comments »

3D photography hot again

Friday, July 17th, 2009

Slashdot has a post on World’s First 3D Webcam. There was a hands-on test of Minoru 3D webcam published on the web. That claimed be the world’s first 3D webcam allows you to takes 3D anaglyphic images that can be viewed with suitable 3D viewing glasses. That technology allows 3D videos and stereoscopic 3D video chat over the Internet. It works. there is a YouTube video at Minoru 3D webcam hands-on web page that can be viewed at 3D with suitable viewing glasses. I found some old glasses that seemed to work so well that I could say that the video worked.

The downside of the technology is that that anaglyphic photography was clearly not invented to create comfortably-viewable Internet videos (besides initial limitations the used video compression technologies can mess up the video quality). And even the anaglyphic photograps are not always nicest one to view. The problem with all 3d is that the lenses on the glasses must be calibrated to the colors on the display for optimal effect. With a properly calibrated display and some good quality glasses 3D effect using this kind of technology can give pretty amazing 3D images, although the colors you see on your eyes are not good. It also takes some calibration until the 3D effect works. For me it took moving my head to different distance from the monitor until I began to see the 3D well.

This kind of stereographic 3D approach does not work for all people and viewing this kind of 3D images can cause disconfort to some people. Stereographic images do fool your brain into getting a depth cue, and it assumes that because it gets depth cues, you should be able to get a different perspective by moving your head. This confusion fades after a short while (depends on the person), but it’ll always be there.

I played with several different 3D viewing technologies in the 1990’s and documented some 3D technologies used at that time. At that time my favourite viewing device was Sega 3D glasses connected to PC. It gave possibility to view quite nicely some 3D photographs and real-time 3D graphics. Then the interest in this type of 3D seemed to fade away for a long time. But it seems that anaglyph images have seen a recent resurgence due to the presentation of images and video on the internet, Blu-ray HD disks, and even in print. There is even a flicr group for anaglyph (Red-Cyan 3D Pictures) images.

3dglass

Posted in Audio and Video, Computers, Entertainment Technology | 4 Comments »

Grounding outside

Saturday, July 11th, 2009

Inside building there are situations where you can see 60-115 V AC between different equipment grounding points. When going outside the building the voltage differences can between different grounding points can become larger. In electrical engineering, Earth Potential Rise (EPR) also called Ground Potential Rise (GPR) occurs when a large current flows to earth through an earth grid impedance. The potential relative to a distant point on the Earth is highest at the point where current enters the ground, and declines with distance from the source. Ground potential rise is a concern in the design of electrical substations because the high potential may be a hazard to people or equipment. The ground potential rise near high voltage substation can be hundreds of volts, even thousands of volts during the ground fault for a short time.

GPR will occur at several locations simultaneously. Fault current will divide among all circuit paths back to the source (metallic and earth return, for example) and create GPRs in the process. Metallic return paths include overhead ground wires, multi-grounded neutrals, bonds, station ground grids, and other conducting materials. Hazardous voltages can appear suddenly as a result of power faults or lightning strikes. Conductive objects (Copper telephone cable, metal, damp saline soils, etc.) can become energized or carry a harmful potential that, if not properly protected, can cause serious injury.

Ground potential rise is also an issue with cell phone base stations. Lightning strokes can hit the base station antenna. And those base stations are also sometimes co-located nearby high voltage electrical lines.

The use of an all-dielectric fiber optic cable in place of a copper telephone cable eliminates the possibility for high voltage to travel from one end of the system to the other. It is of utmost importance to always determine the proper protection scheme when dealing with telecommunication wire line circuits between any location where high voltage and high current equipment is co-located with these circuits. It is always best to design for the worst case situation, since more likely than not, this can happen. Protection against both High voltage and ground potential rise is the best precaution against equipment failures and human injury.

Always when operating with grounding issues remember that there is no absolute ground. There is always a certain amount of resistance to electrical current between all grounding points. This resistance can change with humidity, temperature, connected equipment and many other variables. And there is always a change that some fault current can get to that resistance.

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Parallel port still popular

Monday, July 6th, 2009

The traditional PC parallel port is getting more and more rare on new PCs. It could be said that the parallel port is practically dissappearing from the PC technology. For example my new PC I use (bought more than year ago) did not have parallel port in it. Started documenting parallel port controlling document Parallel port interfacing made easy more than a decade ago. I have updated it over the years many times. And then the new PCs did not anymore have normally parallel ports I though that it is not worth of throuble to keep up the document and control software portcontrol. But for some strange reasons I still keep getting lots of feedback on that document and portcontrol program. So it seems that parallel port keeps interesting people even though it is practically obsolete technology nowdays doomed to go away (according to plans of Intel and Microsoft). Does anyone have any other thoughs on the future of the PC parallel port?

lptcircuit1

Posted in Computers, diy | 3 Comments »