HARDWARE HACKER (EN, Oct. 1993)

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Pulse monitor secrets, an update on free energy, a new wireless communication magazine, thermoelectric guidelines, and aerobic exercise software.

An update to last month's free energy resource sidebar: The International Association for New Science newly released their 540 page proceedings from their latest International Symposium on New Energy. At $49.50. All of the usual topics are covered antigravity, Reed motors, pulsed magnetics, zero point scalar energy, homopolar generators, Tesla earth resonance, perpetual motion, element transmutation, cancer cures, alternate fusion, the whole bit.

My view is that the proceedings are a fascinating and wondrously bizarre work of fiction. Many of the papers presented emit an aura of outright hogwash.

On the other hand, the first step in researching any controversial topic is to find out who is doing what to whom. Even totally absurd and "not even wrong" notions can lead to useful and innovative new concepts. Forums should exist for all controversial thought. Which makes the symposium worth a look.

Thermoelectric review

Judging by the helpline calls lately, there seems to be a lot of interest in the solid-state thermoelectric coolers that are now cropping up in surplus channels.

Sadly, most hackers don't pick up on the fact that there are several very rude surprises awaiting when they try to use these in the real world.

So, one more time: These thermoelectric modules are extremely inefficient and need extremely good heatsinks. They are strictly limited to very low power uses. They also demand simple and obvious heat flux calculations which most hackers positively refuse to make.

For most hacker uses most of the time, the thermoelectric cooling modules simply do not work.

Let's see why this is so.

Solid-state thermoelectric modules using the Peltier cooling effect were developed over three decades ago and have not changed or improved one whit since. The players change every few years in an industry that's been chronically unprofitable. One supplier is Melcor. They offer data sheets and design notes.

Figure 1 shows a typical heat pumping curve for a 20-watt module. Applying a DC current across the device causes heat to be moved from one surface to another. This module might need 15 volts at 3 amps for operation.

Note that the heat pumped depends inversely on the temperature drop across the device. Yes, you can pump 20 watts of heat through a zero temperature difference. Or you can pump zero watts of heat across a 50 degree temperature difference. That would be, of course, with zero efficiency.

More typically, you'll want to both pump heat and have a high delta-T, or change in temperature. A typical operating point might be a 25-degree drop when pumping 10 watts.

The data sheets seem to bury the module efficiency figures for most normal operating points. Often, three watts of energy are required to move one. This is an EER (Energy Efficiency Rating) of a laughable 0.33. Compare this against a US air conditioner with an EER of 12 . Or a Japanese one with a superb EER of 17.

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NEED HELP? Phone or write your Hardware Hacker questions to: Don Lancaster Synergetics Box 809-EN Thatcher, AZ, 85552 (602) 428-4073 For fast PSRT access, modem (800) 638-8369, then an HHH. Then XTX99005,SCRIPT.

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Low efficiency would not be all that bad if all of the excess heat was not generated in the wrong place at the wrong time. But what you have done when you use a thermoelectric module is add heat precisely where you are trying to eliminate it.

It is trivially easy to get more delta-T rise between your module hot side and ambient than the delta-T cooling the module is providing! Let's use an aquarium cooler as an example. Now, there is another name for any large aquarium. It is called a super efficient heatsink.

So, let's take our super efficient heatsink and then remove some heat from it. Because of the thermoelectric module's inefficiency, we may have to add three new watts of heat for every one removed and put it into a new heatsink.

Naturally, we would not want the new heatsink to rise up as far above ambient as the aquarium goes below, or we will simply be heating up the ambient air. So, we'll shoot for an output temperature rise of only a quarter the cooling drop.

Your final heatsink will have to be 16 times better than your aquarium! A handy heatsink would be a second aquarium that is 16 times larger than the one you want to cool.

Just how much heat are we talking about here? That's what doing heat flux calculations is all about.

Let's review the basics.


FIG. 1--TYPICAL HEAT PUMPING CURVE for a larger thermoelectric module. Note that the efficiency goes down as the temperature differential increases.

The two key numbers you have to look for are your watts of cooling required and your heatsink thermal impedance. Going back to square one, a BTU, or British Thermal Unit is the amount of energy needed to raise or lower the temperature of one pound of water by one degree Fahrenheit.

There are around eight pounds of water per gallon, so eight BTU 's are needed to shift the temperature of a gallon of water by one degree F. A temperature rate of one BTU per minute will occur when 17.58 watts of power are input to the system.

Heat flux ends up proportional to temperature difference. For a given heatsink, you'll get twice the delta-T for twice the watts passed through.

Math similar to plain old Ohm's law defines the thermal impedance.

A typical heatsink might have a thermal impedance of between 2 and 10 degrees Celsius per watt. If the thermal impedance is per watt, and if you are transferring 8 watts, the thermal rise will be a total of 40 degrees.

To get below 1 degree per watt, you usually have to go to forced-air cooling. To get under half a degree per watt, a pumped-water cooling system is often the best choice.

The key problem is that the heat rise of the hot side of the thermoelectric module above ambient can easily exceed the net cooling of the module itself! For instance, you might have your module doing a 30 degree cooling, but your heatsink hot side might have a 40 degree rise above ambient. The net result is 10 degrees of heating. That's the exact opposite of what you are trying to do. The module also operates at a much less efficient point on the thermoelectric response curve.

In the case of the aquarium, you can easily measure your heat flux.

The results will depend on the surface area of the aquarium, the ambient air flow, the temperature drop required, and the amount of water present.

Temporarily remove the fish and fill the aquarium with ice water. But otherwise let it run with the usual lights, pumps, and whatever. Next, carefully measure your temperature versus time as the ice melts and slowly reaches room temperature.

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1. The area to be cooled must be superinsulated. All avoidable sources of heat gain must be carefully excluded.

2. Realistic heat flux calculations and heatsink thermal impedance calculations must be carefully made ahead of time.

3. Current thermoelectric modules are an inappropriate solution if more than twelve watts of actual cooling are called for.

4. The rise of the module hot side temperature above ambient must be kept as low as possible. This rise must never exceed a small fraction of the total temperature drop desired.

5. Very large and extremely high quality heatsinking is a must. Use forced air cooling at the very least. Pumped water cooling may be required to achieve an acceptable efficiency.

6. Power sources must have very low ripple and hum, since the ripple peaks heat much worse than the troughs cool.

7. Surfaces contacting the module must be ultra-flat. 100% contact is essential. Thermal grease must always be used.


FIG. 2--USE THESE GUIDELINES for all of your thermoelectric module designs. Otherwise, you are likely to end up heating instead of cooling!

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(A) This approximate block diagram...

(B) Generates this burst of six micropower impulses...

(C) To produce this transmitted waveform...


FIG. 3--THE MYSTERY WAVEFORMS inside a typical "chest type" pulse monitor revealed. The transmitted signal approximates a 36 cycle burst of 5 kiloHertz sine-waves. One burst per pulse event. What you really have here is plain old inductive coupling using an air core transformer.

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The Radio Shack #277-0123 digital thermometer is ideal for this.

Then plot the temperature rise versus the slope of the warming curve at your target temperature, in degrees per minute. To hold the target temperature, the degrees-per-minute cooling needed will equal the degrees per minute warming taking place.

Multiply the pounds of water times the degrees per minute of cooling needed to get the BTU 's per minute required. Multiply that by 17.58 to get the cooling watts needed. Finally, multiply the result by some fudge factor like 1.5 for a safety margin.

The chances are that the final cooling power required will be hundreds of times higher than what can be done using thermoelectric modules.

I haven't actually run this warming test, but I'd guess that 300 watts of cooling would not be an unreasonable value for keeping a large aquarium fairly cool. And if you do burn up 3 watts of inefficiency for every single watt pumped, something like 1200 watts of heat will have to go out through your heatsink. With a 1-watt per degree C rise heatsink, the thermoelectric module's hot side temperature will try to go to 1200 degrees. Thirty of the 20-watt modules would be needed! Do those new CPU thermoelectric coolers work? I'd be willing to bet that if you removed the cooler and coupled the heatsink directly to the CPU case itself, the results would end up as good or better-simply because you are not adding extra heat at a 3:1 premium where you don't want it.

A related story: Years ago there was this total federal solar fiasco involving a school in the rural south.

This was to be a pilot demonstration project of a solar adsorption cycle cooler. The results weren't quite as good as expected, so they added a new five-ton evaporative cooler to the output to improve the heatsinking to ambient air. Sure enough, the cooling then met the specification.

Then someone asked this rather embarrassing question: How much evaporative cooling would have been needed if the solar adsorption cooling was not in use at all? The answer? Three tons! Using thermoelectric modules for many hacker applications can end up the same as building a bonfire inside an icebox.

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PULSE MONITOR RESOURCES

ACT USA

Box 5490 Evanston, IL 60204 (708) 491-9628

Bicycling Magazine

33 East Minor Street Emmaus, PA 18098 (215) 967-5171

Creative Health Products 5148 Saddle Ridge Road Plymouth, MI 48170 (800) 742-4478

Dialog 3460 Hillview Avenue Palo Alto, CA 94304 (415) 858-2700

Medical Electronic Products 2994 W Liberty Avenue Pittsburgh, PA 15216 (412) 343-9666

Medical Equipment Designer 29100 Aurora Road #200 Solon, OH 44139 (216) 248-1125

Polar 99 Seaview Blvd Port Washington, NY 11050 (516) 484-2400

Precise International 15 Corporate Drive Orangeburg, NY 10969 (914) 365-3500

Pulse Stick II /Claggk Inc PO Box 4099 Farmingdale, NY 11735 (516) 293-3751

RacerMate, Inc 3016 NE Blakeley Street Seattle, WA 98105 (800) 522-3610

REI 1700 45th Street East Sumner, WA 98352 (800) 426-4840

Synapse Enterprises Box 35311 Canton, OH 44735 (216) 455-1162

Trek 801 W Madison Street Waterloo, WI 53594 (800) 879-8735

Vetta /Orleander USA 14553 Delano St, Ste 210 Van Nuys, CA 91411 (818) 780-8808

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Are there any applications at all for thermoelectric modules? Certainly. If you have carefully made your heat flux measurements. And if you are moving only tiny amounts of heat out of a superinsulated region.

And if you are dumping into a big heatsink with a very low delta-T. You also have to use super smooth surfaces, proper thermal grease, and avoid all ripple in your power supply. The tiniest amount of ripple will foul things up because the ripple troughs heat six times better than the peaks will cool.

Figure 2 shows guidelines for proper use of thermoelectric modules. These modules can be a surefire winner for any science fair, where you can easily feel all the heat going from your thumb to your finger, even with a single "D" cell.

They are also useful for chilled-mirror dewpoint instruments. And handy in high vacuum applications where moving parts are a no-no.

Thermoelectric modules are great for cooling microscope stages, special astronomy instruments, and infrared detectors. But the modules don't seem useful for cooling the low-noise amplifiers used in satellite dishes because the gain drops faster than noise figure improves.

What are the practical alternates to thermoelectric modules? Small compressors are not that big a deal.

Obvious sources are drinking fountains, refrigerators, icemakers, and reworked auto air conditioners. One source of info on these is HVAC Contractor. A drinking fountain compressor will need only 60 watts of new energy to pump 300. But the neatest substitute for thermoelectric modules are called vortex coolers. These second cousins to perpetual motion machines seem to blatantly violate thermodynamic laws. But, of course, they do not.

A vortex cooler is simply a magic Tee-shaped pipe that contains no moving parts at all. Ordinary air is blown into the middle. Hot air comes out one end, and cold air out the other-down to-40 degrees Fahrenheit.

Leading suppliers include Vortec and Exair. Some important applications for vortex coolers are for cooling electronics and stopping needle breakage on industrial sewing machines.

I would guess that a vortex CPU cooler could be produced very simply and easily. And it would work much better than a thermoelectric module. As far as I know, nobody has even tried.

Pulse monitor discoveries

Warnings: Do not ever modify an EKG-type pulse monitor in any way for any reason! Do not ever attempt to build your own units of this type! What follows is not in any manner to be construed as medical advice.

I've been developing some aerobic exercise software for a client-using PostScript, of course. I have found it to be the greatest universal hacker's language anywhere ever. I have also been looking closely at the pulse monitors and have found some fascinating new electronic concepts that you might like to expand upon in one way or another.

These concepts should apply beautifully to short-haul telemetry applications.

But please be careful to heed all the above warnings.

One way to deal with exercise, of course, is to get yourself a corned beef and pork fat sandwich, add a helping of eggs Benedict, and chow down until the urge goes away.

There are others who feel that sustained exercise programs provide positive benefits towards longevity, physical conditioning, well being, and can be beneficial in medical therapy.

The harder you exercise, the higher your heart rate. The goal of an aerobic (or "with oxygen ") exercise is to reach an elevated pulse rate target zone and maintain it for a fairly long time. Say half an hour to an hour of cycling, group aerobics, swimming, jogging, or fast walking.

A conditioning target zone might be 60 to 75 percent of the maximum heart rate. The maximum rate in turn depends upon sex, age, and upon the advice of your physician or aerobics instructor. For instance, a 30year-old male might have a target zone of 114 to 142 beats per minute.

The old "thumb and stopwatch" method of measuring pulse rate has some problems, not the least of which is that it woefully disrupts the program in progress. There are two alternative methods to measure pulse, the plethsymograph, and the EKG (electrocardiogram). The plethsymograph is based on finger or toe capillaries expanding and contracting with each pulse beat. Shine infrared light through your finger, and its transmission will vary with your pulse. Opacity depends on how much blood is present. The variations can be amplified, conditioned, and digitally averaged to extract the current pulse rate.

The method is cheap, simple, and noninvasive.

Infrared plethsymographs are easy to find, even as $19.95 specials at K mart. Unfortunately, many of these simply do not operate properly in aerobic exercise situations.

The main problem involves motion artifacts. Any relative motion between sensor and finger will give a false output and highly erratic, near-useless results.

Better yet, there are EKG-style or "chest type" monitors that directly measure the electrical activity of the heart. These are usually offered in two pieces, a small chest strap, and a stopwatch-type display that is either worn on your wrist or mounted on the exercise gear.

The cost of these systems is often in the $70 to $200 range. But they are totally free of motion artifacts. And you can instantly check your pulse at any time during the activity by simply glancing at the display. Many systems also offer settable alarms that trip if you wander outside your target zone.

Clock and stopwatch functions are included.

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FIG. 4--AEROBIC EXERCISE RECORD written in PostScript. Fully editable source code appears on GEnie PSRT.

Marvin Gribiinski Tuesday, June 22, 1993 Route: Whitlock loop Distance: 7.4 miles.

Maximum speed: 14.5 mph.

Average speed: 11.0 mph.

Miles to date: 1145 EXCERCISE TIME IN MINUTES

Previous resting pulse: 74 Previous standing pulse: 86 Recovery pulse at 0 seconds: 110 Recovery pulse at 20 seconds: 107 Recovery pulse at 40 seconds: 104 Recovery pulse at 100 seconds: 97 Comments: Good day. Mild winds. Loose gravel improving.

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One typical unit is the Edge Heart Rate Monitor distributed by Polar and stocked by such yuppy outdoor stores as REI. I tried that one in combination with a Trek bicycling computer. A second brand is Favor.

Combination monitor and bike computers in one unit are available, such as the Vetta HR-1000 also offered by REI. At $95 list.

How do they work? The chest unit is totally sealed and has an internal battery. In normal use, it gets replaced every year or two. The internal battery is purposely not replaceable to guarantee that the unit remains un-modifiable.

There are very stringent regulations that govern anything electronic that directly attaches to your chest.

Obviously, the chest unit acts as a transmitter and the wrist unit serves as a receiver. The effective range is typically four feet or so. But what gets transmitted how? The answer to this one is yet another stunningly beautiful find in our ongoing quest for elegant simplicity.

What we really have here is short-haul telemetry. But one that has to remain totally sealed, be compact and lightweight, reliably run under micropower, and literally be a throwaway item with a five-buck maximum manufacturing cost.

The secret is a plain old inductive coupling. Figure 3 shows the secret waveforms involved. What you really have here is a 5-kilohertz air-core transformer, with the primary in the chest unit and the secondary in the wrist or handlebar receiver. Each pulse is converted into a 36-cycle burst of 5kilohertz sinewaves.

You can easily monitor these waveforms. Just take any old coil, such as a fifty foot roll of hookup wire. Add an iron core, such as a handy pair or pliers. Center the coil near the chest unit. And then watch the results on your scope.

A pair of conductive pads pick up the EKG signals on either side.

These microvolt-sized signals are strongly amplified in a bandpass amplifier. There is probably some type of AGC (Automatic Gain Control) loop to standardize the output levels. Then, a comparator of some sort derives a digital output for each pulse event.

Each pulse event then generates a series of six digital impulses. Each impulse is around 80 microseconds wide and has an inter-pulse spacing of one millisecond for a one-kilohertz repetition rate.

If very low power is your goal, you cannot use any kind of linear amp for your transmitter. Instead, the antenna is simply a 5 kilohertz resonant coil. The plots found in my Active Filter Cookbook tell us the Q of this coil is around 20 or so.

To transmit a signal, the resonant antenna coil gets whapped once every five cycles. The high Q of the coil fills in during the intermediate cycles. If you look at your scope display carefully, you will observe the modest exponential decay of the intermediate cycles between impulse whappings. The long rundown time after the last whapping is also quite obvious.

Only the bandpass amplifier draws continuous current. Both Maxim and Linear Technology make suitable amplifiers that consume only microamps. In absence of any pulse input, there is no output and no transmitted signal. Even when a burst is sent, the duty cycle to generate the burst is 10:1 and the duty cycle of the burst itself is typically 80:1 or so.

The average current ends up quite low. Very elegant.

X-raying the unit revealed a few surprises. A large lithium coin cell is used. The antenna is a ferrite rod with its long axis horizontal that is apparently tuned by unwrapping a few turns. It is resonated by a polystyrene capacitor. A 14-pin integrated circuit drives the antenna. It is probably a plain old grunt CMOS quad gate.

The majority of the input circuitry is discrete and consists of nine SOTs (Small Outline Transistors) and 24 assorted resistors and capacitors. Special techniques are required for proper noise rejection and ultra low power operation.

The receiver is just a resonant coil and a bandpass amplifier that inputs into typical micro-current stopwatch circuitry. The amplifier apparently shuts itself down in the absence of any transmitted signals. The receiver battery can be replaced and lasts a year or more. An averaging algorithm is used to smooth out the results for a stable display.

A sample printout for a routine exercise session is shown in Fig. 4.

The complete PostScript code to custom run these on your favorite word processor appears on GEnie PSRT as #751 EXERCISE.GPS. You could build up an automatic data acquisition system to automate the whole process. But it is simpler and cheaper just to use a one-hand cassette recorder every five minutes and talk the speed and pulse rate to it.

I've gathered several places to go for more information on pulse monitors into our resource sidebar for this month. Creative Health Products offer a free comparison guide for many popular monitors.

This month's contests Let us have a bunch of different contests this month. Show me some other uses for inductive coupling in short-haul telemetry. Or find me the actual schematic of some EKG-type pulse monitor. Or find a hackable source of pulse monitor chips.

That should be ideal for one of my isopod power line monitors.

Or run the aquarium ice warming test. Or show me a genuinely useful hacker application for thermoelectric modules that works in the real world. Or show me some other off-the-wall uses of PostScript for new data-to-plot applications.

There'll be all the usual Incredible Secret Money Machine ll book prizes along with an all expense paid (FOB Thatcher, AZ) tinaja quest for two going to the best of all.

New tech lit Up the Infinite Corridor is a new book on the history of engineering at MIT by Fred Hapgood. It's a really good read. But by far the best part is Fred's revival of a very ancient seven-word definition of what engineering is all about: A sense for the fitness of things. That says it all.

Lots of night vision electronics and surplus infrared viewers are available from Resources Unlimited.

A free brochure is available.

There's a new $9.95 book on the history of Heathkit from Heath Nostalgia.

Antique Radio Laboratories has a free catalog on its products for radio restoration buffs. Included are custom pins, adapters, bases, and coil forms. They also stocks manuals for older test equipment.

The Oughtred Society exists for the collectors of traditional slide rules and calculating instruments.

It's named for the seventeenth century slide rule inventor. Meetings and classified ads cost $20. Motorless Motion is a project book from Mondotronics on working with the shape memory "muscle wires" for robotics and similar uses.

Included are fifteen easy-to-build projects and layout templates. The book is $18; $29 for the book and wires.

From TriQuint Semiconductor, a new Data Communication Products data book. It's mostly on new microwave integrated circuits such as low-noise amplifiers, mixers, down-converters, and AGC stages.

Wireless Design & Development is a new trade journal on new products for the emerging personal microwave communication services.

As we've seen a number of times in past columns, any hardware hacker involvement with the patent system is virtually certain to end up a net loss of time, energy, money, and sanity, mostly because of all the outrageous popular mythology that surrounds patents and patenting.

I have put together a new Case Against Patents reprint package that includes several hundred pages of proven alternates to patenting. A big directory of hundreds of inventor organizations is included. See my nearby Synergetics ad.

A reminder that I have arranged for a new and faster GEnie signup for my PSRT RoundTable. Refer to the Need Help? box for full details.

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Also see: COMPUTER CONNECTIONS

BIPOLAR TRANSISISTORS


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