Flash point and volatility

In your September 2005 article on the Bilge Sniffer, there seems to be some confusion with volatility and flash point. The flash point of petrol is somewhere in the vicinity of 150°C, whereas the flash point of diesel is about 70°C. The definition of flash point is "the temperature at which, if a drop of fuel is touched to a surface of that temperature, the fuel will self-ignite or flash".

Note that it does not need a flame or spark. And notice how diesel fuel is more dangerous if let loose onto hot surfaces.

However, there is a feature of fuels that we don’t usually know and that is vapour pressure, which is linked to volatility. Its definition is "the pressure required to hold vapours in a liquid at a specific temperature". This is about 10psi for motor spirit at 38°C, whereas kerosene and similarly diesel have a much lower pressure of 0.2psi at 38°C. Volatility is "the tendency for fuel to vaporise under given conditions".

With all this, gaseous fuels are usually more dangerous than liquid fuels, as most gaseous fuel mixtures that are commonly used are heavier than air and flow to the lowest point in closed vessel; where our noses cannot readily detect them.

For all this, I think that John has done a great job with the detector.

Brian Bannister,

via email.

Comment: you make some valid points although there was no specific mention of volatility or flash point in the article.

Visual Basic for the Electrocardiograph

I read the question and answer on this topic in "Ask SILICON CHIP" (September 2005, Page 106) response with interest, being a Visual Basic Programmer and electronics hobbyist. It was good information about the USB interface being supplied with a driver to emulate a serial port.

However in the interest of the by-now-confused reader who asked the original question, I need to correct some of the information supplied. DCOM 98 has nothing to do with the COM port.

It’s another confusing computer acronym. DCOM stands for Distributed Component Object model. 500-page books have been written to try to explain its purpose and operation, so let’s just say it allows you to run a software component installed on one machine from another.

The component you were referring to is in fact the MSComm.ocx control that shipped with the professional edition of VB3 and above but not always with the standard edition.

It allows communications with a serial port. If you don’t have the pro edition, don’t despair. Like most things in Visual Basic it can be done in code. A quick search of the internet will provide the answer. I found this page that provides a down-load and a quick tutorial: yes-tele.com/mscomm.html

I hope this helps. I find the ability to communicate with electronics projects via the PC very interesting.

I would often like to modify the software in the same way many people will modify the project. To this end I would love to see more source code published with your projects, even if it is via your website. There are lots of home automation projects that lend themselves to being controlled via Visual Basic.

Max Healey,

via email.

Comments on Ask SILICON CHIP

I have some comments on the August 2005 issue.

In "Ask SILICON CHIP" on page 104, P. D., raised the subject of processing delays in plasma displays. One would hope that the display manufacturers would supply a delay facility for the audio to match that of the video (but that would probably only be 2-channel). Your advice of trying the proposed screen with your audio equipment seems to be fairly impractical.

If this problem is as widespread as you indicate, given your position as the leading technical publication in this field, it would be good if you could do some research or your own tests to actually quantify the delays involved. Lip sync problems are usually only apparent when the differential delay exceeds 100ms.

Apart from the problems with plasma processing times, the studios themselves are usually the biggest culprits in causing additive differential delay, due to too many frame stores in series without using expensive audio tracking delay lines that are matched to the frame stores.

Also on page 104, C. D., spoke of a subwoofer problem. It wasn’t clear that the special cable he was using was shielded. If not, shielding may help. Beyond that, converting the interconnection to be balanced could be a solution.

On page 105, G. C. wanted help with eliminating interference to video signals. Hard-of-hearing people do not need more bass, so a high-pass filter on the input to the induction loop amplifier could be a solution to keeping the low frequencies out of the loop. A compressor on the feed to the induction loop amplifier would be an alternative to the high-pass filter.

It would seem to me that an induction loop that produces a signal 10 metres outside the building is being driven with far too much power and just a simple attenuation of the input to the amplifier may be a complete solution.

Run the video in balanced mode on a twisted pair. A couple of SILICON CHIP advertisers offer video baluns/VGA extenders that will convert the signal to balanced to easily cover many times the distance specified.

On page 106, P. M. queried a tapping halfway up the chain of cells in a battery. In some packs, I have found that this is simply for a lower speed option on the drill. This is poor design as it can lead to half the cells being discharged while the others are left fully charged.

Finally, the article on your Carbon Monoxide Alert project suggests that drivers put their car ventilation onto recirculate when high CO concentrations are detected. This seems to be dubious advice as that would lock you into a closed, relatively low volume where there was no chance of lowering the concentration. If this is necessary, it should only be used for a very short time. Ideally you should sense both inside and outside the vehicle and select which ever gives you the lowest concentration.

Running on "recirculate" is meant to be only for exceptional conditions, as it can be quite dangerous if there are any CO leaks into the cabin from the vehicle’s own defects.

On the latest cars, even if you select "recirculate", this will be periodically overridden by the HVAC computer to ensure that the cabin air is purged to minimise the risk of passengers being affected by any buildup of harmful gases.

Graham Goeby,

via email.

Valves, nostalgia and self-deception

Remember when hifi was a glorious mixture of science and art? All the clever compromises that were made to approach fidelity: big transformers with taps all over the place, rats’ nests of components at the back of a rotary switch to cope with various response curves from various record companies, weird shapes for styli, strange tonearms, tonearm counterbalances, turntables straight from Heath Robinson, etc.

To understand the concepts involved, you had to be an enthusiast but not much more. You could talk about it, fiddle with it and feel that you were a part of a world-wide community of cognoscenti. At the centre of it all was a valve amplifier. We used to joke that we wanted to replace it with a "straight piece of copper wire, with gain" but we really didn’t.

Remember how much of that science and art was devoted to overcoming shortcomings inherent in the valve amplifier? Well, now we have it: the bits come off the CD and go through to the back of the speaker as if via a straight piece of copper wire with gain and we have nothing to talk about. All we can do is listen to the music.

Which reminds me of something else: remember how many of those enthusiasts never actually listened to music?

Tony Turner,

via email.

Comment: yep, we remember that ideal: a straight wire with gain. Many people apparently don’t want straight wire.

New preamp does not have phono stage

I don’t believe it! Your new preamplifier (SILICON CHIP, October 2005) comes without an RIAA/phono input preamp! If SILICON CHIP has presented a valve amplifier design (from the era when 78 RPM recordings were the norm), why would you not include an RIAA input on a contemporary preamplifier?

33 RPM vinyl disks are enjoying a resurgence of interest and many people (myself included) still have an extensive collection of vinyl recordings. Sure you could convert them to CD format (you would still need an RIAA preamp) but to do so well takes time. For a disk you might only listen to once a year, it is probably not worth the effort.

Another oversight in the design of this preamplifier is the absence of an attenuation network on the CD input, so that the higher output level which may be presented by some CD players can be equalised to the lower output levels of the other audio sources.

Regarding the Mudlark valve amplifier (SILICON CHIP, August & September 2005), adverse comments from audiophiles with golden ears have been remarkably absent. Silicon diodes in the power supply? Valves mounted on a PC board? Don’t 555 ICs oscillate? No-one has noted the use of fluorescent lighting ballast chokes as inductors in the design.

What sacrilege! Can you imagine how this will affect the ambience ratio? (This measure quantifies the difference between what you think you hear and what you actually hear!) Now if the inductors were wound with oxygen-free copper on polypropylene formers and then dipped in Peruvian beeswax (chosen for its superior sonic qualities), praise and approval might be forthcoming from the golden-eared brigade!

Peter van Schaik,

Tenterfield, NSW.

Comment: it is true that there is continuing interest in vinyl records. That is why we produced the LP Doctor project in the January & February 2001 issues. It can easily be hooked up to the new preamplifier and together with its ability to reduce clicks and pops on old records, represents the best approach for playing records.

Valves and self-delusion

I just wanted to add my five cents to the whole valve versus solid-state debate that seems to be happening at SILICON CHIP these days. I had never heard valves before I made the hifi version of the Valve Preamplifier described in the February 2004 issue of SILICON CHIP. I built it with no great expectations, beliefs, prejudices, etc. I just thought it would be fun and interesting.

Well it turned out to be the best sounding preamp I have had in my system! Please note that I say best sounding, not best measuring! I build hifi components to save money and listen to music, not to impress anyone with spectacular measurements. I run the preamp into a Rotel power amplifier and also into the SILICON CHIP headphone amplifier (May 2002).

I certainly don’t think I am deluding myself. I can’t see the valves in operation because they are hidden away in a metal case, nor can I feel their warmth! In fact the whole thing is in a cupboard which is just as well because the power supply is annoyingly noisy.

I sure do hope you continue with valves, especially small-signal stuff like preamps and headphone amplifiers. I would love to see a valve equivalent to Peter Smith’s current solid-state preamp, with relay switching, headphone amplifier, remote volume, etc. Surely you realise there is a market there regardless of how deluded you think it is?

Rob Knutsen,

Doncaster, Vic.

Scanners worth salvaging

I am a fan of recycling and enjoy the "Salvage It!" articles. There are a lot of older scanners ending up on the kerbside lately (driver incompatibility with XP perhaps?) and there are some great components in these that can be recovered.

There is a cold cathode tube with an inverter (usually 12V or 24V to power and a pin to short to turn it on), front surface mirrors (OK for light/laser experimentation) a good lens, a stepper motor (often geared) plus a drive pulley and belt, a LED/phototransistor limit detector, switching power supply and other components.

I don’t have a particular project in mind but thought that the above may be of interest or maybe trigger an idea for Julian Edgar.

Russell Verdon,

Wollongong, NSW.

Alternative satellite image site

Your article on Google Earth in the October 2005 issue was very interesting. However, it failed to mention the www.ozabove.com satellite service that is available to Australians free of charge, delivering about 20 images daily, much more up-to-date than Google.

The image resolution is 1km per pixel. That’s better than what the BOM (Bureau of Meteorology) has and it can be very useful for anyone interested in the weather as well as sea surface temperatures. For example, fishermen should find that very useful for locating warm waters meeting cold in the southern ocean.

The site is currently used by the Siding Spring Observatory as well as the Mt Stromlo Satellite Laser Ranging facility, as it delivers the resolution and timeliness required for their applications.

Balthasar Indermuehle,

Glebe, NSW.

Gobsmacked by Google

I’ve just had a glance through my new edition of SILICON CHIP and noticed that I am not the only one amazed at Google Earth! Look at these grid positions: 32d 10’N 110d 50’W and you will see the B52 bomber junkyard. Then check 32d 08’53.06"N 110d 49’58.44"W and you will see B52s that have been cut up. Something to do with a weapons of war disarmament I am told.

Gary Ferguson,

Shepparton, Vic.

BPL promotion from the masters of spin

Congratulations on your article about Broadband over Power Lines in the November 2005 issue. At last someone outside the amateur radio community has spelt out the problems with this technology.

The proponents, who appear to be masters of "spin", have had it all to themselves for too long. Have you ever seen a press release from them that didn’t mention 200Mb/s speeds? How on earth they would achieve this speed, except perhaps in a very controlled environment, eludes me and I am sure it has more than a few network designers scratching their heads.

The only way I could see that speed being achieved is if they "squirt" enough RF energy into the system to make the actual wires redundant! And to hell with everyone else trying to use the radio spectrum.

The "large scale trial" in Tasmania is also one that has been carefully chosen as to avoid or minimise any adverse effects. For a start, the wiring in that estate is underground and the plans they offer are so expensive that you would have to be a millionaire if you wanted to watch streaming video or download the odd movie. So, they are certainly trying to keep the usage down, perhaps to avoid showing up the flaws when the network gets busy.

The other "furphy" that gets bandied about a lot is "universal availability" and the press and politicians seem to be buying it. After all, there are not many places without power lines. Why it would be cheaper to wire up Birdsville with BPL than say ADSL or wireless no-one explains.

Surely, if it is not economical to enable a country telephone exchange for ADSL, it can’t be so for BPL. They seem to want to convey the impression that they can enable universal internet access no matter where, with the flick of a switch! Power switch, that is.

I just feel sorry for the investors who will pour money into this technology based on the current hype, without realising the many flaws that do exist.

Horst Leykam, VK2HL,

via email.

BPL is mains-borne interference

Several years ago, I submitted an electronic Electric Fence Monitor unit in for a C-Tick compliance certificate from the ACA and most of the testing seemed to be about the level of electrical interference that may get into the mains side.

It seems Broadband over the Power Lines would go against all the principles of mains-borne interference suppression and the regulations – see: www.acma.gov.au

Peter Robertson,

via email.