DVD player features pitch control

I’m still buying cheapo DVD players and continue to be dumbfounded by both what we’re getting and for how much! Some months ago, I was at Lake Cathie (just south of Port Macquarie), where they had just opened a new Woolworths supermarket, and they had some door-buster opening specials.

Among other things they had "Nu-Tec" DVD players for $69. They had every possible signal output configuration, vacuum fluorescent display, two Karaoke Mic inputs, electronic echo and tone controls AND variable pitch playback that works on both DVD and CD!

I really don’t understand how this works. With DVDs, the audio pitch can be changed dramatically but the frame rate remains rock-steady and artefact-free at 25 fps. The first DVD I tried it on was "2001: A Space Odyssey" and through my big stereo system, all the big orchestral numbers pitched up and down faultlessly. There wasn’t a trace of the irritating whistling and chirping that used to plague the expensive studio pitch-altering devices of a generation ago when you tried to process more than one voice or instrument at a time. There must be some damned clever DCT manipulation software in there. (It would certainly settle those perennial 24 frame film/25 frame video arguments). All for $69 and with a great picture too; clean as a whistle.

It works the same with CDs, flawlessly changing the pitch but not the actual speed of the music. The echo is a bit basic; it only works on the microphone inputs and you can only alter the delay, not the actual echo level, but what do you want for that price? In normal Karaoke use (if there is such a thing), it’s actually quite effective.

I managed to steam off the "warranty void if removed" label and take a peek inside. The assortment of PC boards is interesting. The main DVD player board is beautifully made, screen printed/green lacquered with plated-through holes and an assortment of SMD chips, a 27MHz crystal and not much else. How the hell do they get the 4.43361875MHz and 3.579545MHz colour/color subcarriers out of the same 27MHz?

The mains power supply module is a more humble TV-set-like brown phenolic non-SMD job, the vacuum fluoro and front control button PC board is very much Big-W Chinese clock radio standard, while the Karaoke mic input and level pot board looks more like something out of a 1970s Hong Kong pocket radio!

Actually, my Aldi player still wins on two points: (1) it remembers where you were up to on a disk even after the power has been switched off; and (2) they supplied the two AAA cells for the remote!

Keith Walters,
via email.

TV interference may have a simple cure

I am writing regarding the item on a TV signal strength meter on page 88 of the December 2004 issue. It reminds me of a problem I had with Channel 10 in Melbourne some 10 years ago which has probably been covered in SILICON CHIP before but here goes.

I have multiple home outlets and at some time I noticed annoying herringbone patterns across the screen but no audio interference. I started down the path of antenna checking (testing others before actually buying) and balun and cable replacement (not always easy).

Having run out of options, I called on Mr Antenna (before he became famous). He told me it was just interference from the FM radio transmitter co-existing on the TV station’s transmitter at Mount Dandenong. The fix was an FM trap at about four dollars. Do you think I wasn’t annoyed? The TV station’s sympathetic chief engineer said they were aware of the problem but management didn’t want to publicise it or the fix.

S. K. should check that he is not experiencing some similar phenomenon.

Peter Brett,
Melbourne, Vic.

USB-controlled power switch

I have just built the USB-Controlled Power switch published in the November 2004 edition with the modified PC board from the Notes and Errata in the December 2004 edition.

Congratulations to Jim Rowe on a very simple idea put to great use. Referring to the problems with some PCs always having power on the USB port to power such devices as USB mouse chargers, I had this exact problem. All you need to get around this problem is a spare PCI slot and a cheap $20 USB add-on card. Run the power switch from this card. When you turn your PC off, the 12V power is removed from the USB ports and the Power Switch shuts down.

This now gives me 11 USB ports on my PC and no glowing peripheral in the corner of the room at night.

James Deland,
Old Reynella, SA.

Wind power is cube of the speed

In the December 2004 article entitled "Build Yourself a Windmill Generator", it mentioned that the power in the wind is proportional to the square of speed. In fact, the power is proportional to the cube of the wind speed so that when the speed of the wind doubles, the energy and thus the power is increased eight-fold (2 x 2 x 2 = 8).

Consider this: the kinetic energy from the wind is E = ¹/₂ x mass x wind velocity². The mass of the air is equal to the density x volume of passing the area swept by the blades or, wind mass flow = density x pr² x wind velocity. So the energy in the wind is
P = ¹/₂ x pro x pr² x wind velocity³.

This means it is important to protect the windmill structure in gusty places as the energy in the wind varies with the cube of the wind speed. Imagine an energy level which is 27 times more than the one you designed it for when the wind speed triples, which is what usually happens in typhoons.

Demetrio Chuasieng,
Tsing Yi, Hong Kong

Video cameras can check IR remote controls

For those who don’t need the completeness of the Remote Control Checker kit featured in the January 2005 issue, a digital video camera will do the same job. Simply point the video camera towards the IR LED in a dimly lit area and you can see the LED flash. The camera receives the IR signal and converts it to a white light on the LCD display. I presume the video camera supports IR reception for Night View camera modes.

This is cheaper if you already have a video camera, more expensive if you don’t. A friend mentioned this to me some time ago when I was building a IR controller to turn things on/off from my computer and I wondered if it was transmitting the wrong codes or nothing at all.

David Robinson,
Alstonville, NSW.

Editor’s comment: good point. When I was editing this article I made a mental note to include a panel mentioning that you could check IR remotes with a video camera. As you can see, I forgot.

Short life from CFLs

I couldn’t agree more with Leo Simpson’s write-up in the August 2004 issue on compact fluorescent lights and with what other Mailbag writers have had to say on the subject to date. We have tried a couple of the CFLs to replace normal incandescent bulbs and they didn’t last as long as the original incandescents.

However, on reflection, we really didn’t give any thought as to where one could "properly" replace incandescent bulbs with CFLs.

In reality, CFLs are just miniaturised standard fluorescent lights with electronic control thrown in. And where does one usually find standard fluoros used the most? Generally, they are used in areas where they are turned on and left on for several hours at a time; eg, supermarkets, shops, car parks, hospitals, factories, street lights and so on.

The way the CFLs are packaged and advertised, one can only believe that you could save heaps of money if you were to replace all the incandescent bulbs in your house with CFLs. I feel that advertising for CFL products should include a recommended minimum operating period per day to achieve the advertised lifetime.

Rod Josey,
Killarney, Qld.

Cheap components and inaudible beepers

I wish to express my concern about three matters that no one but me seems to find worth raising.

No 1. Never mind about fancy hifi low loss cables. When are manufacturers going to produce flexible flex? Years ago, we used to be able to put our soldering iron down and it would stay where we put it.

No 2. When are manufacturers going to produce RCA and similar plugs and sockets that do not get distorted when you try to make a good soldered joint to them?

No 3. When are designers who put beepers into equipment finally realise that people of my age cannot hear a sound when the beeper is operated? This can be quite critical when beepers are used in household alarm systems.

Evan Prout, Wellington,
New Zealand.

Extra low voltage limit is 50V AC

I note the letter from Brian Clancy in the Mailbag pages of the January 2005 issue, quoting 32V AC as "extra low voltage" That information is four years out of date.

The following is an extract from AS/NZS 3000. 2000 Wiring Rules. Note that the DC voltage limit for ELV is higher than for AC volts.

1.4.90 Voltage

Difference of potential normally existing between conductors and be-tween conductors and earth as follows:

(a) Extra-low voltage not exceeding 50V AC or 120 V ripple free DC.

(b) Low voltage exceeding extra-low voltage, but not exceeding 1000 V AC or 1500 V DC.

(c) High voltage exceeding low voltage.

Reg Brownjohn,
Charlton, Vic.

Energy Meter calibration queries

I recently built the DSE version of your Energy Meter (July & August 2004). While the kit appears to work very well, I have a few minor suggestions and observations.

(1) Firstly, may I suggest that a better location for the VR1 contrast trimpot is on the solder side of the display PC board where it remains accessible after assembly.

(2) In my opinion, the design of the battery backup circuit should include an enable/disable switch so that the meter can be stored without having to first open it and disconnect the battery.

(3) The function of R2 is rather obscure. It appears to be there for noise cancellation but what kind of noise? The LPF at the inputs to the op amp should reject RF noise, so as far as I can see, the only other possible noise source is radiated AF. If R2 is intended to cancel the hum from T1, then I would think that R1 and R2 would need to be located symmetrically with respect to the transformer body. As it is now, R1 is about twice as far away as R2.

(4) The power calibration procedure is somewhat questionable. My feeling is that the level of accuracy (using a radiator) leaves a lot to be desired. The primary factors affecting the meter’s accuracy are the internal reference voltage of IC1 (2.4V ±200mV) and the tolerances of the scaling and sensing resistors.

Rather than use the 2.2MΩ 400V 5% resistors supplied in the DSE kit, I would use DSE’s 2.2MΩ 600mW 1% Cat. R0258 resistors. I would then match the actual measured values of the resistances on each leg of the amp so that the ratio of 2.2MΩ to 1kΩ is as close as possible on each side. After assembling the meter, I would carefully measure the reference voltage on pin 9 of IC1 and use this alone to calibrate the meter.

My Vref was 2.41V which suggests that no calibration should be necessary in my case. If on the other hand, the measured value was 2.50V, say, then I would think that the power reading should be increased by a calibration factor of (2.50/2.40)² = 1.085.

Having said this, I am puzzled as to why the default power calibration setting is -600 counts. Why not zero?

Franc Zabkar,
via email.

Comment: as with all types of meters, calibration is required. In particular, the Energy Meter needs calibrating to compensate for tolerance in IC1’s voltage reference, the voltage division and current sense resistors and so on. The initial calibration of -600 was to prevent constructors having to calibrate any more than necessary.

The tolerance of IC1’s internal reference is the main reason for calibration. Using 1% 2.2MΩ resistors would not alter this. The balanced current lines using R2 actually works well even though the circuit looks strange with a 0.01Ω resistor in series with 1kΩ.

Calibration using the radiator is accurate if the procedure is followed carefully.

Warnings on 240VAC not too cautious

I must agree with Brian Shirley (Mailbag, December 2004) that "Warnings on 240VAC (are) not too cautious." The casual attitude many people have to the potentially lethal mains supply is almost unbelievable.

His story of his misadventures with the lighting fixtures and cables illustrate errors and methods of testing that are all too common, even these days.

In the 1960s, the broadcasting station where I worked purchased an AC appliance tester. Not only would this test for wiring transpositions or disconnections on the power outlets, it also tested appliances for leakage to ground and for integrity of the appliance’s earth connection.

From memory (now rather hazy after so long), the leakage test used a neon lamp feeding the linked Active and Neutral legs of the power input, which would glow if the leakage to ground exceeded a few milliamps.

The earth integrity test used a low-voltage source to measure the resistance between the appliance’s earthed metal parts and the earth pin on its power cord, on a "good/bad" meter. From memory, the meter would indicate in the "good" part of the scale for a resistance of 3Ω or less.

I have not seem any similar testers either "in the flesh" or in advertisements. Maybe they rejected too many appliances that people judged to be "safe enough."

Greg Mayman,
Adelaide, SA.

Keep up the high voltage warnings

In regards to the issue of high voltage warnings for certain projects, keep doing it! I have had many accidents through complacency and have survived, fortunately. It cannot be expressed more strongly, high voltage IS dangerous and all care MUST be exercised.

I haven’t had any misfortunes with high voltage for a few years but that is only because I try to be very aware of the dangers and I do exercise utmost caution. But one day, I may again become complacent and I’ll get bitten again, perhaps fatally next time.

Always beware of high voltage. If it doesn’t kill you, it’ll hurt like hell and leaves you feeling very unwell, possibly for some days. It is also possible that you’ll suffer some cardiac damage that may not show up for some time.

Ian Dempsey,
Dubbo, NSW.

Atlas LCR meter a thrill

What a thrill to open the August 2004 issue of SILICON CHIP and see my circuit idea published. An added thrill was to have won the Atlas LCR meter. It arrived a few days ago and I have had fun using it. Thanks for a great magazine and thanks for my prize.

Robert Gatt,
Port Fairy, Vic.