Saturday, March 27, 2010
LM3909 Replacement
I have a four-page "spread" in next month's Everyday Practical Electronics (EPE) magazine -- previously published in Silicon Chip (SC) magazine. It's an LM3909 replacement module -- that is, it does what a very popular chip once did -- only better. However, EPE and SC broke with my original concept, by spreading it out on a 5cm by 6cm PCB. My original design (pictured) intended for the new "LM3909" be built on top of a 16-pin DIL socket -- in other words, little larger than the original. So here, for interest, is my original idea (pictured) -- but for copyright reasons, you'll need to refer to EPE or SC magazines for the details of how the circuit works. OBSERVATION: My original idea would require a little ingenuity to implement -- but no problem for an electronics engineer.
Friday, March 26, 2010
Berg River Moonrise
I stumbled upon this photo that I took of a moonrise over the Berg River swamp / wetland, about 150km / 90mi north of Cape Town -- where I have gone to rest and write in the past. I waited in black darkness, surrounded by eerie noises. At this moment, the moon appeared above the fog. You may click on the photo to enlarge to VGA.
Thursday, March 25, 2010
Father K.
I took this photo of a good friend, Father K., at Hartebeespoortdam, in the north of South Africa. Perhaps he is looking cheerful here because he is not lost (for much of our outing, he was)! The photo showcases my compact Leica's magnificent lens. You wouldn't get such a shot with just any compact camera.
Tuesday, March 23, 2010
Franciscan Homily
.I attended a Franciscan mass on Sunday (pictured). The service was held in several languages, mostly African, with African drums and hearty singing. The priest who delivered the homily said: "If you don't treat Lent seriously, you'll stay in the grave. You won't rise with Christ." I said to another priest: "Didn't that seem to you like salvation by works?" He replied: "That message would have been more appropriate before Lent, not at the end of it."
Monday, March 22, 2010
My Supervisor
This one's a tribute to my academic supervisor, Dr. Vincent Atterbury (on the right of the photo). Fuller Theological Seminary in the USA taught me many things, but they did not teach me rigour. I was unprepared for studies at the South African Theological Seminary. With this in mind, uppermost in my mind when I think of Vincent (as he is to me) is the fact that he looked at my potential at the beginning, not my actual competence (this is not always the case with supervisors, or seminaries). Also, he taught me the rigour that I so much needed and wanted. His competence as a supervisor is proved by my excellent results. To give an example (I'm not quoting verbatim), I sent him a draft of my thesis, saying: "Here's a completed draft. Now you can see it in full." He turned straight to the bibliography, and spotted an error. He returned it, saying, "It needs to be perfect. Then I'll look at it."
Sunday, March 14, 2010
BFO With Wobbulator
Talk about a wobble causing a flutter. After referring to a wobbulator in one of my posts, I received a number of requests to explain it. Surprisingly, I don't see much about wobbulators on the Internet -- so, I'll offer a circuit which employs a wobbulator -- a BFO metal detector that I designed (pictured). In a comparison with six commercial designs of the 60's and 70's (before BFO went out of fashion), it out-performed four. But first, the wobbulator. A BFO metal detector uses two high frequencies running side by side (oscillators IC1.A and IC1.E in this case, which both run at about 250kHz). One of these frequencies (IC1.E) shifts when metal is picked up, while the other (IC1.A) remains the same, and so a difference frequency is created. This, one hears in a pair of headphones. That's the theory, anyway. In practice, however, there's a thing called frequency lock, where those two frequencies "lock on" to one another -- they get stuck to each other like magnets. The difference frequency thus fails to materialise until the difference is comparatively large. It's a nuisance, because it may severely affect sensitivity, and is not easy to overcome. However, a wobbulator, since it introduces a wobble into one of the frequencies, unsettles the frequency lock, and may do a lot to "bust out of it". OBSERVATION: A wobbulator might benefit almost any kind of detection circuit -- including the Matchless Metal Locator recently described on this blog. IC1, in this circuit, should ideally be a CD40106BCN or a HEF40106BP to obtain optimum performance -- otherwise R3 may need some alteration. The potentiometers' metal cans would ideally be wired to 0V. Click on the image to enlarge. The details of the coil are at Tri-Coil. . NOTE: You may re-publish this design, on condition that you acknowledge the designer, Thomas O. Scarborough.
POSTSCRIPT: See Silicon Chip magazine March 2023 for a six-component BFO design in which I use regeneration to double the typical detecting range of BFO.
Tri-Coil
This is a description of the coil that accompanies my BFO With Wobbulator design. It needs to be emphasised, though, that this is an "off the wall" experimental design -- just to test various concepts. The detector uses a triple, concentric coil, with the three coils being wired in series as shown, with 33swg (30awg/0.254mm) enamelled copper wire. A tri-coil vastly improves the detector's response to small metal items. Each coil is bound with insulating tape, then individually wound with a Faraday shield, made of strips of tin-foil, and bound once more with insulating tape. Each Faraday shield should cover all but about 5% of the circumference of a coil, thus leaving a gap between the start and finish of the shield. All three shields are wired to 0V. The coils are fixed to a non-metallic base plate. Screened two-core audio cable is used to connect the tri-coil to the circuit, with the screen being attached to the Faraday shield. A single coil of 100 turns 150mm dia. may also be used.
Wednesday, March 10, 2010
Hermanus Anglican
This is St. Peter's Anglican Church in Hermanus, a major coastal town about 100km/60mi east of Cape Town. The foundation stone is dated 1933. The tower was built in 1937. The tower makes the Church more typically English in style, as Anglican Churches in South Africa usually have a bell turret instead of a tower. You may click on the photo to enlarge to 70k.
Monday, March 8, 2010
Matchless Metal Locator
This is one of my best super-simple metal detector designs, which a publisher generously donated to the public. Before this design came along, induction balance (IB) metal detectors typically used 50-100 components. The simplicity was achieved through several tricks -- but in summary, I stripped out the usual analogue electronics. Copyright restrictions prevent me from publishing the design on my blog, but it may be downloaded free here: Matchless Metal Locator. OBSERVATION: What I can offer on my blog is nearly ten years of hindsight. I would now improve the design, most importantly, by increasing the battery voltage to 12V or 15V, and using a 9V regulator. This would greatly assist stability. The biasing around IC1 pins 8 and 12 could be simplified by combining VR1 and VR2 in one 500k component. And if I had the chance, I would like to apply a wobbulator to the IC1b input circuitry. This has been a popular design. It went into production in Australia, in two versions.
Wednesday, March 3, 2010
Bredasdorp Anglican Church
The photos show All Saints Anglican Church in Bredasdorp, from opposite ends. Bredasdorp lies in the southernmost district of Africa, and according to Collins Maps has between 10,000 and 20,000 inhabitants. The Church was built in 1861. Although I attended this Church (see Anglican Church) I have no further information on it. You may click on the photos to enlarge to 130k.
Monday, March 1, 2010
Robber Fly
I snapped this Picture-Winged Robber Fly in our back yard this morning (using filler flash). It is the first time I have seen one. In fact this one is way, way out of its normal range. It shouldn't be here. One normally finds it in the north-east of the country. Its speciality is snatching spiders from their webs -- and one thinks spiders catch flies! You may enlarge the photo to 40k by clicking on it.
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