An EE’s Guide to Survival Between Microphone and Voice Coil is an interesting slide set amde by Netherlands´ well known audio engineer Bruno Putzeys and put to web by Hypex Electronics and Grimm Audio. It was presented in AES convention at 2007. It is a very good presentation of the whole audio electronics path from microphone to speaker. If you are into audio electronics, read this slide set.
Use right ground symbol in your electronics schematics and other drawings.
Earth-ground symbol represents a real connection to earth. That connection could be for example 10-foot-high copper-clad steel bar driven into the earth (at your premises or nearby provided by power company) or metal water lines. That earth ground is wired to the neutral of your house wiring at the breaker panel. You can reasonably use the earth-ground symbol for the ground pin on the electrical outlet. Your electronics equipment schematic should use the earth-ground symbol to indicate connection to the electrical outlet ground pin on equipment plugged to wall outlet.
It is bad practice to use earth-ground symbols for chassis common. You an use the chassis common wherever a power supply or circuit card connects to the chassis. In a circuit board schematic you can use chassis symbol when a standoff screws the PCB to the chassis.
Signal-ground symbols are most suitable for most circuitry on a PCB. A design can have several of these symbols, with notations to identify them.
Information source: EDN magazine article Draw the line: Isolation shields systems from shocking surprises
Ground 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.
Remember that a real life return path for current is not an ocean of zero impedance. Some engineers draw every ground as a wire because even copper planes have impendance. This approach might be one reason that makes some audio engineers more think of using single-point grounding. By discarding ground planes in favor of thin traces that wind back to a single-point ground, some audio engineers get slightly better distortion measurements, but at the expense of poor immunity to RF. The problem is that every audio circuit must work at 2 GHz — not to pass any signal but to reject noise from cell-phone radiation. Remember that every one of those long, spindly “ground” wires is an antenna. For RF noise immunity performance ground planes and connectors tightly connected to equipment metal case are good things.
Ground loop elimination in video systems does not always ask for a complete isolation of the grounds. There are passive hum suppressor transformers that will very effectively remove the hum from the video signal, but do not affect the video signal otherwise. Those special transformers act like a common mode coils, which stop the annoying ground loop currents on the shield of the coaxial cable, but provide a straight path for the signal inside the cable. This type of device is capable of passing the signals from DC to tens of MHz without problems. The hum suppressor transformer both reduces the current flowing on the cable shield and compensated the voltage differences that would otherwise be between cable ends and eventually get to the signal.
The humbugging transformer/coil consists just of many (tens to hundreds) turns of 75-ohm miniature video coaxial cable wind on a suitable transformer core. The aim is to have a coil that has high enough inductance to keep the cable shield current low and still withstand the voltages/currents it gets exposed to in typical applications without saturation. This kind of hum reduction coil works by mutual inductance. The coax cable is wound around a transformer core so that both the inner and shield of the cable become inductors. The tight coupling ensures that any voltages/currents flowing on the cable shield, caused by variations in earth potential differences, are transformed into the inner conductor. This type of transformer is typically constructed to a specially selected toroid transformer core.
This type of hum suppression transformer has found it’s way to the professional video application (rental companies) and computer video applications (computer to video projector connections). The transformers of this type are usually called “hum bug transformers”, “hum-bucking transformers”, “anti-hum video transformers”, “hum suppressor transformers” or “video isolation chokes”. T The humbugging transformer presents a simple transmission line to the signal, so that its signal amplitude capability is essentially unlimited, and its bandwidth extends from DC to that frequency where line losses become excessive. Isolation increases with increasing noise frequency. The choke provides protection against moderate levels of 60 Hz hum, and protection against very high levels of RF noise. ypical performance figures are 30-40 dB hum level reduction up to 2-10V volt voltage differences at mains voltage frequency (50 Hz or 60 Hz). The maximum voltage the humbugging transformer can handle at low frequencies depends on the transformer specifications, usually limited by transformer core saturation. The humbugging transformer choke is primarily used in Broadcast TV because it passes the DC component of the signal. It is used in studio, and in remote ENG.
This picture shows the inside a commercially sold “video hum bug transformer” sold by Finnish company RGB. The price range of this kind of commercial device is usually 100-200 US dollars range. I had to open this unit to change the BNC connector that was broken on a field use. This device consists of a toroid shape transformer core and around 50 turns of very thin 75-ohm video coaxial cable wrapped around it. You can make your own working similar device by taking he core from a 100-400W toroidal mains power transformer and winding 30-50 turns of thin 75-ohm coaxial cable around it. This will work well but is somewhat larger and heavier than the commercial devices like this. It is possible to optimize the size with careful selection of suitable core material and number of turns.
Here is an inside views of some humbugging video transformer products that I have made. They have performed very well on many video systems to solve ground loop problems.
RC filter or amplifier’s lowpass filter at the input of a delta-sigma ADC is normally put there to reduce noise. But sometimes adding a filter can produce a noisier digital output than without that filter. Using an analog filter to inject noise article tells that it is as easy to eliminate higher-frequency noise with an analog lowpass filter as it is to inject noise into the frequency band below the corner frequency of your filter. If you change your circuit design by reducing your filter’s resistor values, you will increase the noiseless bits in the circuit.
Researches are developing a new generation of contact lenses built with very small circuits and LEDs. They promises bionic eyesight in the future. Bionanotechnology researcher Babak A Parviz writes about his research toward producing a computer interface in a contact lens at IEEE Spectrum article Augmented Reality in a Contact Lens. The author states that, ‘All the basic technologies needed to build functional contact lenses are in place,’ and details what refinements and advances will be necessary to bring this technology to reality. The picture below is from the article.
More 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.
Resistance soldering is a soldering method that sometimes useful for hobby work. In this soldering methid an electrical current is flowed through one work piece, the joint and then the other work piece. Current through a resistances on the way generates heat. Most heat is normally generated on the joint because the resistance there is typically the highest.
Resistance soldering web page describes the technology in details. Resistancesoldering.com/ tells that resistance soldering can work also on some PCB work and similar applications. Resistance soldering is claimed to be good for soldering RF connectors, for example connectors on semi-rigid bases and central contacts on coaxial connectors. The soldering operation consists of clamping the parts to be assembled and adding a solder alloy. The heating process starts as soon as the foot pedal is activated and the temperature rises to the set temperature point. Look the video tutorial on soldering RF connector with resistance soldering.
According to Resistance Soldering Set document a resistance soldering set consists of a transformer that supplies 3 or 6 volts at a high current to stainless steel or carbon tips. The transformer is turned ON by a foot switch and OFF by an electronic timer (up to few seconds time). Since the soldering tips are hot only during the brief period of actual soldering, burning of wire insulation and melting of connector inserts are greatly reduced.
Build your own resistance solderer tells you how you can make your own resistance soldering iron with minimal investment. Resistance Soldering Unit is another page that gives instructions to build your own resistance soldering iron.
Assembly TV broadcasts TV program from Assembly computer festival starting Thursday 6. August 2009 in many channels (Internet, cable TV, DVB-H mobile television, 3G mobile video etc.).
The broadcast has for many years contained Scene Quiz Show (the name has varied somewhat over years). It involves three contestants answering questions related to the event, demoscene and computers. I have worked with that show many times. When the show started we needed the answering buttons and lights like any real TV quiz show has. I built the first light system based on some really old PC (Sinclair PC200). The answering buttons connected to RS-232 port handshaking line. The parallel port data pins were connected to drive Velleman K2634 four channel triac card that switched the mains power to lamps on and off. The software for the PC was written using Turbo Pascal programming language, it was a modified version of some of my light control software I used to control some lights on parties in the 1990’s. The system had three buttons for competitors and three corresponding light outputs. In addition there was a “effect” output that give power for few seconds after each keypress, that could be used to control light and sound effects that tell that one competitor has pressed button. The system was built up very quickly, but it worked well in live TV broadcast without any problems (other then I was the only I could set up the whole system correctly).
Some years later the system was updated. The new setup was built around old Toshiba T3200 classic laptop PC. The answering buttons were still connected to serial port like earlier but were made much better looking. The light controlling part was updated. The actual mains power controlling was handled by my four channel light dimmer that accepts standard 0-10V control signals. The 0..5V signals that come from PC parallel port were converted to 0-10V and isolated with help of Kemo M125 relay module that plugs to PC parallel port. This was proven to be a well working system that was used for many years to come. The show is going to air this year as well.
The following images are from year 2001 show where the quiz show light were used first time if I remember correctly (images from Byterapers gallery).
Here is one picture from summer 2009 broadcast. In this broadcast the hardware was mostly the same, but that old laptop was replaced with a newer PC running a new control software.
