Friday, November 13, 2009

A Seed-Catcher for Pole-Mounted Bird Feeders

We have two "shepherd's crook" type poles supporting bird feeders in our yard. The one in the back yard (shown below) provides sunflower seed, and the one on the east side of the house provides nyger seed. I have tried various methods of dealing with the seed hulls and uneaten seed that falls below the feeders, but I think the new seed-catchers that I have designed and built are the best solution. I am providing the design details here for the many other birdwatchers that have pole-mounted feeders.

From Seed Catcher Project

The Problem:

Among the seed hulls that fall to the ground are uneaten seeds or fragments, which attract mice and rats. Also attracted are ground feeders such as pigeons, grackles, and starlings, which because of their mobbing behavior tends to frighten away the more desirable songbirds. A screen a few inches above the ground with a mesh large enough to allow the seed to fall through will deter the ground feeders. But the mesh must be smaller than one inch and the sides also enclosed securely to prevent small birds from being trapped inside. However, to deter rodents from tunneling into the enclosure, the bottom must also be secured. The bottom must also allow rainwater to pass through. Also, there is the problem of how to dispose of the fallen seed when the enclosure becomes full of old seed.

My seed-catcher design solves all of these problems, using two 3-by-5 foot wooden frames that fit on either side of the pole, covering a 6-by-5 foot area. Notches on one side of each frame allow the frames to fit snugly around the pole. Hardware cloth with a half-inch grid covering the top and bottom of each frame allows seed to fall through while excluding ground-feeding birds and rodents. Above the bottom hardware cloth is a sheet of porous plastic that prevents seed from falling through the bottom onto the ground or into a rodent tunnel, but allows rainwater to drain. The fabric/plastic sold as "weed stop" fabric for use under stone or mulch beds works well here. Both hardware cloth and weed-stop fabric are available in 36-inch wide rolls.

At the center front of the pair of frames, extra boards closely spaced will support you when you need to refill the feeders, but old seed can fall between these boards.

To dispose of the old seed, turn each frame over, dumping the old seed onto a tarp or plastic sheet. Then, folding the sheet in half, you can dump the sheet into a waste container. No shoveling or sweeping of the ground is needed.

Materials List:

6 8-foot lengths of "1-by-4" inch lumber (actually 3/4" by 3 1/2")
4 pieces of 36 inch by 5 foot hardware cloth, with 1/2 inch mesh
10 feet of "weed-stop" fabric, 36 inches wide
64 wood screws, 1 1/2 inches long, (1 box, Philips head recommended)
about 150 galvanized staples, 1 inch long (1 box)
about 15 to 20 feet of tape that can stick to plastic and wood.

The "weed-stop" fabric may be called by other names. It is a porous plastic or fabric intended for use under stone beds, paving stones, or mulch to allow rain water to drain while preventing weeds from penetrating.

Cutting list for the six 8-ft lengths of "1-by-4" lumber:

Each line lists the cuts for one 8-ft board:

60" + 34 1/2"
60" + 34 1/2"
29" + 29" + 34 1/2"
29" + 29" + 34 1/2"
24" + 24" + 24" + 24"
24" + 24" + 34 1/2" + 6 3/4" + 6 3/4"

Save two pieces of scrap for temporary use.

The last 34 1/2" piece should be rip-cut in half lengthwise, so that each half will be about 1 3/4" wide.

The two 6 3/4" pieces don't need to be exactly that length. Just cut the remainder in half, and they will be about 6 3/4" each.

Recommended tools:

tape measure
square
carpenter's pencil
circular power saw
1 or 2 corner clamps (holds 2 pieces at right angles)
battery-powered drill
battery-powered screw driver
(two power drill/drivers saves changing bits)
drill bit, size to match shank of screws
hammer
scissors or knife (to cut tape)
tin snips (heavy-duty scissors for sheet metal, to cut hardware cloth)

From Seed Catcher Project

Construction:

All of the following diagrams show edge-on views of the lumber. They are not exactly to scale. (The thickness of the lumber is somewhat exaggerated.)

Predrill holes for all screws using a drill bit that matches the diameter of the solid center of the screw. I hold a screw and the drill bit parallel to each other up to the light to check that the drill bit does not obscure the threads of the screw.

Align two 29" pieces over a 60" piece, supported by the 6 3/4" piece and two scrap pieces as shown, centering the 6 3/4" piece under the 2" gap. Fasten the 29" pieces to the 60" piece with 2 screws on each side of the gap. This makes a 60" side with a notch at the center. If the screws go in too far, they may attach slightly to the 60" piece. If this happens, pry them apart with a screwdriver. Be careful of the protruding screw points when handling; but these points will end up inside the finished frame where they will be harmless. Make two notched sides like this.
From Seed Catcher Project

Next, assemble a basic frame using a notched 60" side, a one-piece 60" side, and two 34 1/2" end pieces. Be sure the notch is facing outward. A corner clamp is useful for holding two pieces together at each corner while drilling and screwing. Use 3 screws at each corner. Make two frames like this.
From Seed Catcher Project

Three 24" pieces are added to each frame to create an area that will support you when you refill the feeders. Space these 4 inches apart (3 3/4" between boards), starting at the notched side. Fasten with 3 screws each. Do two frames as shown.
From Seed Catcher Project

The frames are identical until the pieces shown in blue in the next diagram are added. These narrow pieces come from a 34 1/2" length of 1x4 lumber that is cut in half lengthwise. Orient the frames with the notched sides facing each other as shown. (When pushed together, the two frames will wrap around the pole at the notches.)

First. hold each narrow piece over the side where the 24" pieces are fastened, and copy the spacing onto the narrow piece. Then fasten each narrow piece to the free ends of the 24" pieces at the top of the frame so seed can pass below it. Use one screw for each piece. Last, fasten the ends of each narrow piece to the long sides, using one screw at each end. The frames are now mirror images of each other, and the narrow pieces mark the top side of each frame.
From Seed Catcher Project

Cover the bottom of each frame with a 3 by 5 ft piece of porous "weed-stop" plastic, holding in place with pieces of tape about six inches apart all around. Then cover with a 3 by 5 ft piece of hardware cloth as follows. First, un-roll the hardware cloth so that it is nearly flat, or slightly curled. (I sit with the roll in my lap and push the hardware cloth over my knees, working from side to side and gradually toward the other end, with the semi-flattened part extending away from me.) Anchor one corner of the hardware cloth to one corner of the frame with a screw (a washer on the screw helps), with the hardware cloth curling upward, then stretch out the hardware cloth and anchor the opposite corner in the same manner. Then anchor the remaining two corners. Check that the hardware cloth fits the long sides well; it can over-shoot the short sides at first.

Fasten the hardware cloth along the long sides, except for the corners, using 1-inch staples about six inches apart. (The staples also hold the "weed-stop" plastic in place, so the tape was needed only temporarily.) Next, remove the anchor screws and trim the ends of the hardware cloth with tin snips, cutting next to a parallel wire to avoid making sharp points. Staple the short ends. If any hardware cloth protrudes past the edge of the frame, use a hammer to bend the hardware cloth down over the edge. First angle the hammer to bend it half-way, then make another pass over it to bend it all the way.

Cover the top with only hardware cloth, in the same manner.

Saturday, October 17, 2009

My Favorite Invention

(UPDATE: I've added some photos to the end of this blog.)

My favorite invention is my Phase Meter (U.S. Patent 6,441,601), for a number of reasons:
  • It began as a simple insight, which led to further discoveries, and then to more complex implementation.

  • Its performance seems almost magical to me.

  • About a half dozen of these phase meters are being put into all new GPS satellites, where they will improve GPS accuracy, especially for military guided weapons.

  • It exemplifies how designs grow top-down rather than bottom-up.
Also, a number of friends and relatives have asked me to explain at least one of my inventions. With the help of some video demonstrations, I will explain the basic concepts of this invention in simple terms and how it gradually leads to more complex details (but I won't get into the details). The reader will get an understanding of how basic concepts are developed into working designs.

The Phase Meter compares the timing of two very different clocks with a surprising degree of accuracy. In a GPS satellite, accurate clock timing is necessary for accurate measurement of global positions, that is, for accurate navigation. The Phase Meter is accurate to within five picoseconds. (How small is that? Well, if you had a rocket that could go from New Jersey to California in one second, it would go only a hair's breadth in five picoseconds.)

Some Clock Basics

Basically, a clock is a device for counting oscillations. For example, a pendulum clock keeps track of the passage of time by using gears to count the swings of a pendulum. Traditionally, we divide each day into 24 hours, each hour into 60 minutes, and each minute into 60 seconds. So we adjust the length of the pendulum as best we can so that each swing to the left and right takes exactly one second; then we count 60 swings for each minute, and 60 minutes for each hour, etc.

The more precise digital watch uses digital counters to count the oscillations (vibrations) of a quartz crystal. (Instead of tick, tock, tick, tock, etc., digital oscilators create a 1010.. repeating sequence.) The rate of oscillation can be set by the cut of the crystal (and other factors), and good performance is obtained at about ten million oscillations per second (10 megahertz). So the crystal oscillator is typically set to 10 megahertz as accurately as possible, and ten million oscillations are counted to measure one second before counting off minutes and hours.

The most precise clocks now are atomic clocks, so called because they are based on the oscillation of atoms, typically rubidium or cesium atoms. However, the oscillation rate cannot be set to some convenient figure such as 10 megahertz. Instead, the rate is set by the laws of nature. For example, the oscillation rate of the cesium atoms in an atomic clock is 9,192,631,770 oscillations per second. The figure for a rubidium atomic clock is also an 'odd-ball' number.

The GPS Clock Situation

In each GPS satellite, a crystal oscillator with 10,230,000 oscillations per second is used to control the timing of the signals sent to GPS receivers. The timing accuracy of these signals determines the accuracy of all GSP navigation. The 10,230,000 rate is a convenient number for generating the signals, but the crystal oscillator isn't nearly as accurate as the atomic clocks on each GPS satellite. So the crystal oscillator clock needs to be compared to the atomic clock and then adjusted to make it just as accurate as the atomic clock.

But comparing these clocks with very different rates is tricky -- it's like comparing a poorly made yard stick, with inch markings, with a more accurate meter stick with centimeter markings.

Here is a video showing two rulers representing two clock signals. One ruler is represented by alternating blue and green line segments of equal length, equivalent to the 101010.. sequence of one of the GPS clocks. The other is represented by marks at equal intervals on a red line, each mark equivalent to a moment when the other GPS clock changes from 1 to 0. As you play the video, notice how the marks on the red ruler sometimes align with a blue section on the other ruler, and sometimes a green section. Suppose we colored the marks to match the color opposite it on the other ruler. Then we would get a sequence of blue and green marks in a seemingly random sequence. In a similar manner, whenever one GPS clock changes from 1 to 0, the state of the other clock is sampled, generating a seemingly random sequence of ones and zeros.

video

Observations Leading to the Invention

Sometimes a mark on the red ruler comes very close to a blue-green boundary, so that a small shift of one ruler relative to the other will change the color sequence. Likewise, a small shift of the timing of one GPS clock relative to the other changes the seemingly random sequence of ones and zeros (the 'sample' sequence). Because the sample sequence is sensitive to timing shifts, I tried to discover some way to decipher the sample sequence to measure the timing shift. The next videos illustrate the method that I discovered.

Suppose the blue/green ruler were wrapped around a circle with a diameter such that the blue segments always fall on one half of the circle and the green segments always fall on the other half of the circle. Suppose that the red ruler is also wound around the same circle. (Imagine that the rulers are so thin that they don't stack up on the circle, not making the path around the circle progressively longer.) Actually, we don't need to wrap the blue/green ruler around the circle; we can just mark the two halves of the circle blue and green to indicate where the blue/green ruler lands on the circle. When we wind the red ruler around the circle, we can see where the marks land on either the blue or green half.

In the video, the halves of the circle are marked as blue and green; and as the circle 'wheel' turns, winding on the ruler, the marks are moved slightly inside the circle when they land on the blue half, and are moved slightly outside the circle when they land on the green half. When you play this next video, notice that even though the marks are fairly far apart on the ruler, they become spread around the circle and eventually become closely spaced. It is this close spacing that allows more precise measurement than expected, because it is normally expected that the precision is the same as the ruler spacing.

video

So how can we calculate the offset alignment of the rulers from the positions of the green and red (one and zero) samples? Here is an analogous example that may suggest a method:

Suppose the famous "Old Faithful" geyser in Yellowstone Park in Wyoming erupts every one hour and 13 minutes exactly. (Actually, that's close to the average interval, but it varies, usually between 65 and 92 minutes, and sometimes about 45 or 125 minutes.) Now, suppose that the first eruption on some day is 41 minutes after midnight, and some one records a list of all the eruption times starting on that day and for one week, using a digital watch. They give us a copy of the list that doesn't include any of the numbers, but only the am/pm indicators, and ask us to figure out the time of the first eruption.

It's really simple to find the answer. We assume that the first eruption is at midnight, and advancing around a 24-hour circle at intervals of one hour and 13 minutes, we mark these locations on the circle "am" or "pm" according to the list. Unknowingly, we have started our list 41 minutes early, but when we look at our circle and see that the "am" marks begin at 11:19pm instead of midnight (12am on digital watches and clocks), it becomes obvious that our list started 41 minutes early, so we conclude (correctly) that the first eruption must have been at 12:41am.

How the Phase Meter Works

The phase meter uses a similar method. Starting at a "zero" position on the circle, positions are computed that are associated with "one" and "zero" samples (analogous to the "am" and "pm" marks). An early version of the invention used a list of these samples, which would become more costly with more samples. A later improvement reduced this cost by eliminating the list, making it practical for millions of samples to be processed.

In this later version, the circle is divided into three equal parts, and the number of "one" samples falling in each third of the circle are counted, using three counters. We figured out how to estimate the angle of the line that best divides the region of the 'one' samples from the region of the "zero" samples from these three counts. (This is a little tricky, but we will skip these details.)

In the next video, you can see these three counts increasing as the samples arrive on the circle, and you can see the estimated angle (computed from these counts) becoming more accurate as the counts increase. The marks outside the circle represent "one" samples, which are counted, and the marks inside the circle represent "zero" samples, which are not counted. The thirds of the circle are divided by black lines, and the estimated angle is indicated by a magenta line.

video

You can see that the result is not perfect, but in this demonstration, we have only 50 samples. A phase meter in a GPS satellite can process about 30 million samples every 1.5 seconds, and the error is about one ten-thousandth of the circle.

Conclusion

When all the details are worked out, we get something fairly complex, even though the initial concepts were relatively simple. The following is a "block diagram" of the final design; there are more details inside each rectangular block:


The yellow area and the blue area below it do most of the operations illustrated by the last video above, exept that the computation of the estimated angle is done by a computer elsewhere. The areas above allow a computer to set up the measurement parameters, and the areas on the left control the measurement timing. (Click on the diagram for a larger view.)

Designs like this are not developed one detail at a time, but rather one idea at a time. The big idea leads to middle-sized ideas, ... and finally to lots of details. That is the essence of what is called "top-down design".

============================================

I recently found some photos from the time that the phase meter prototype was tested. Here is a photo of the phase meter prototype 'test bed'. Most of the circuit board is a microprocessor with its support circuits (because part of the phase meter function is software). The phase meter hardware is the small black integrated circuit in the white square at the upper-left corner of the gridded area at the near end of the board.


The next photo shows the test team gathered around the test bed, with related instrumentation in the background. In the foreground is John Petzinger, co-inventor for the second phase meter patent, who worked with me in Clifton, NJ. I don't recall the names of the other two, but one is a software engineer from San Diego, CA, and the other a hardware engineer from Ft. Wayne, IN. We worked together by email and occasional phone call for months, before meeting for the first time in Clifton for the test.


Finally, I found this graph showing the results of one of the tests. Two stable clock signals with different frequencies were compared by the phase meter prototype at 1.5-second intervals ('epochs') for five minutes, and the variation of the measurements were recorded here. Assuming that neither clock signal was jittery, we assumed that all the variation was due to phase meter errors. Sometimes the error was plus or minus two picoseconds, but the average (rms) was 1 psec -- that is 0.000,000,000,001 second.

Sunday, September 06, 2009

Creation vs. Evolution -- an Overview of my blogs

I've worked as an engineer for 43 years (getting about the same number of patents) designing computers and similar electronic devices that are controlled by information (that we call software) and/or that process information (that we call data). I've even written software that creates other software, and software that creates hardware designs.

In my retirement years, I've been studying the basics of biology and applying my expertise in information systems to investigate the fundamentals of the creation/evolution debate. I look at how living things work from the molecular level on up, and as a systems engineer I recognize a system design when I see one. Living organisms are also controlled by information and process information. Chemistry does the 'hardware' function, and DNA (with its derivatives) does the 'software' function.

I have published my findings, as well as common-language interpretations of other technical sources, on my blog. My blog talks about many other subjects, too, so if you are only interested in the creation/evolution/information stuff, go to the "Find by Subject" section on the right and click on one of those key words. Or you can start with the following overview of a few basic subjects:

Information From Randomness?
In this blog, I discuss the myth that information can somehow arise out of randomness, and discuss Dawkins' Weasel Algorithm in particular. In information theory, pure randomness is zero information. All systems that process information have a tendency to lose information, like the way they lose useful energy. So information always drifts toward randomness, not the other way around.

In The Beginning Was Information
Back in Darwin's day, evolution seemed somewhat plausible, just as the ether and phlogiston were once plausible. But more modern findings have unraveled the claims of evolution (macro-evolution, to be more precise), primarily the discovery that biology is chemistry guided by information. Since we know that information doesn't come from nothing, it begs the question: where did the information come from?

Is Encoded Information an Essential Part of the Universe?
In a previous blog, I had explained that space, time, matter, and energy are inseparable aspects of the universe. Here I argue that information is transcendent to all these. The transport of information across space (communication) and across time (storage) uses various forms of matter and energy for conveyance; yet none of the physical laws that govern space, time, matter, and energy require information to exist. Indeed, in vast regions of the universe where there is no life, there is no [encoded] information.

Can Chemical Evolution Work?
Here I discuss Miller’s Experiment and related issues. The outcome of these experiments is like making jumbled piles of bricks, but no houses. The fundamental reason why experiments such as Miller’s don't make life out of non-life is that the chemistry isn't getting the informational guidance that it needs.

Life is more than chemistry
This expands on the previous blog. Life isn't just chemistry, but chemistry guided by the information stored in the DNA.

The Genetic Code - how to read the DNA record
Here I try to explain, in plain language as much as possible, how the DNA information is read and interpreted by the Genetic Code to construct the peptide chains that are the basis for all organic molecules. It is fascinating that there are potentially a vast number of possible genetic codes, or 'DNA languages', that would each work equally well; yet all living things on earth use the same 'language', and there is no evidence that there ever was any other 'language'.

The First Digitally-Controlled Designs
Here I observe that "The interpretation of the DNA information according to the Genetic Code creates a enormous set of specific proteins and other complex organic molecules that implement the structure and function of a particular organism" and that "All of these complex functions are guided not exclusively by chemical laws, but also by the information from the DNA." I point out that this is not only design, but digitally-controlled design; and I tell how in my engineering experience, I learned to appreciate that this is an optimum design paradigm. The first digitally-controlled designs were not computers, or the Jacquard looms and player pianos that preceeded computers; but were the living things that God created.

The Digital Control of Life
Here I provide further evidence of the similarity of the design of life and that of digital controllers.

Tuesday, August 25, 2009

My Latest Project -- A Portable Cold Frame

First, if you are not a gardener, you may be asking "What is a cold frame?" A cold frame is something like a miniature greenhouse, typically used to start plants from seed earlier in the season than out in the open, by providing a warmer, more protected environment. If a heater were used to provide warmth, it would be called a hot frame; but a cold frame just captures the heat of the sun through a window, and a simple enclosure helps to retain the warmth.

Sometimes an old window is simply placed over a bottomless box made of boards set on edge, and seeds are planted in the earth enclosed by these boards. But I wanted a portable cold frame that could be placed over a stone walkway, and moved under the deck when not used. Other suburban gardeners, and city gardeners, with limited space, might want to set up such a cold frame on a patio or paved area, and store it elsewhere. perhaps standing on edge, when it is not used. So I'm publishing my design to share it with others -- here in this blog, and in a Picaso web album.

I decided to use deck planking for the sides, because this lumber is generally treated for weather resistance, and use to plastic for the window -- the kind made as a substitute for window glass. I wanted the cold frame big enough to comfortably hold nine seedling trays (in a 3-by-3 arrangement), the kind that you get from greenhouses or gardening stores. That closely matches a 3 by 4 foot window piece.

The bottom of the cold frame is covered with 'hardware cloth', a wire mesh with 1/2-inch spacing, to allow drainage and support for the seedling trays. But that would allow stray dirt to fall through, which is not good if used over a stone or paved walkway or a patio. So 'weed-block' fabric is lain over the hardware cloth. This kind of tough porous fabric is made for use under a bed of loose stones or paving stones to allow drainage while preventing the soil from mingling with the stones, and blocking access to the soil by any seeds that fall among the stones. For the cold frame, we get drainage without allowing soil to fall through.

All my garden areas are automatically watered, controlled by timers, either by porous 'soaker' hoses for the larger areas, or by a drip system for containers and the raised-bed herb garden. So I naturally wanted a watering system for the cold frame. But this is an optional feature; the cold frame can be built without it, and you can water it with a watering can or a hose with a spray attachment.

To make the cold frame portable, it is made of three stacked frames, each one of which is not too heavy to carry. The frames begin as identical units:
From Portable Cold Frame

One of the frames is cut on an angle, like this:
From Portable Cold Frame

Then the parts are rearranged to form this sloped shape, which becomes the top frame, with a sloping window:
From Portable Cold Frame

The bottom of the bottom frame is covered with hardware cloth, held in place with stop moulding (the kind used as a door stop on a door frame):
From Portable Cold Frame

The "weed-block" fabric is stretched over and stapled to a frame of 1/2" x 1/2" moulding, and placed inside the bottom frame:
From Portable Cold Frame

Nine seedling trays fit inside the bottom frame:
From Portable Cold Frame

The middle frame has a vertical piece fastened in each corner that protrudes one inch above and one inch below the middle frame. These verticals lock the middle frame in place to the frames above and below it, like this:
From Portable Cold Frame

(The aluminum rail in the above photo is an optional support for the watering system.)

Two ventilation holes are formed in the rear wall of the top frame by cutting notches in the facing edges of the two planks of the rear wall:
From Portable Cold Frame

A slot is cut across each notch by dropping a circular saw into the plank edge, then a piece of hardware cloth is inserted into the slot, like this:
From Portable Cold Frame

The piece of hardware cloth is captured in place, with no need for fasteners. I like minimalist designs like this.
From Portable Cold Frame

Two vertical pieces hold the two rear planks of the top frame together. These verticals protrude below the top frame, and together with the rear verticals of the middle frame, form hinges. One hinge is show here, as well as one corner of the watering system at the top of the middle frame:
From Portable Cold Frame

The edge of the plastic window is sandwiched between 'stop' moulding (below) and 'ply cap' moulding (above), which are nailed to the top edge of the top frame:
From Portable Cold Frame

The next photo is looking through the top window toward the inside of the front wall of the cold frame. Here we can see a length of 1/2" x 1/2" moulding fastened to the inside of the front edge of the top frame with two screws. Below that are two pivoting pieces of 1/2" x 1/2" moulding fastened to the inside upper front edge of the middle frame with one screw each. The pivot screws are off-center, so that pointing the short end of the shorter pivot piece upward props the top frame open with a 1-inch gap, and using the longer end of the shorter pivot makes a 2-inch gap. Similarly, using the longer pivot piece provides 3-inch and 4-inch gaps when propping open the top frame.
From Portable Cold Frame

A larger prop is used to hold open the cold frame, as shown in the next photo. This also shows the inside painted black, to increase the heat energy absorbed from the sunlight coming through the window.
From Portable Cold Frame

The above photo also shows the watering system attached to the top frame, where it is lifted up when the top frame is lifted. Earlier, I had mounted the watering system on the middle frame, where it needed to hinge separately, and needed a second prop:
From Portable Cold Frame

The watering system is built on an aluminum frame that supports nine spray heads, each centered over one of the seedling trays:
From Portable Cold Frame

The spray heads, hoses, and connectors are made by RainDrip, which calls the spray heads "misters". Here is a close-up of one of the 'misters', and a wire loop that joins two pieces of the aluminum frame:
From Portable Cold Frame

The 'mister' comes mounted on a plastic stake, which I cut short and fasten to the frame by inserting it through an X-shaped hole in the frame. Each 'mister' head emits eight radial streams of water, and can be rotated to adjust the flow, or even to turn it off.

The 'misters' are connected by quarter-inch tubing to a half-inch supply line, which connects to regular garden hose, as shown here:
From Portable Cold Frame

For more details, you can view the entire Picaso web album by clicking on the link under any of the photos above. Also, we give more details of the cold frame design (except for the watering system) next, including:

Dimensions
Shopping list
Cutting lists
Tools needed/suggested
Construction



Dimensions of the cold frame:

Seedling trays have various designs, but are generally 10 1/2 by 13 1/2 inches, and 3 1/2 inches high. If we allow 11 by 14 inches for each tray, it will allow for some size variation and room for fingers when handling them. So a 3 by 3 configuration of trays will comfortably fit in a 33 by 42 inch space, and a 2 by 4 configuration of trays will fit in a 28 by 44 inch space; and a 33 by 44 inch space will accommodate either configuration. My design adds an extra inch to this.

Width and length: 34 by 45 inches inside, 36 by 47 inches outside.

Inside height is 2 plank-widths plus 1 inch in front, and 4 plank-widths minus 1 inch in back. Some planks are 5 1/2 inches wide; these provide a height of 12 inches in front and 21 inches in back. Allowing 3 1/2 inches for the seed trays and 1 1/2 inches for the watering system, this allows 7 inches of height for seedling growth. Some planks are 5 3/4 inches wide; these provide 1/2 inch more height in front and 1 inch more in back.

For outside height, add the thickness of the "stop" moulding and hardware cloth at the bottom, and the window frame thickness ("stop"and "ply cap" mouldings) on top. This is about an inch.



Shopping list for the cold frame, not including the watering system:

6 8-foot lengths or 4 12-foot lengths of decking planks, weather-treated; 5 1/2 or 5 3/4 inches wide and 1 inch thick. Choose straight, unwarped pieces.

2 8-foot lengths of "ply cap" moulding
(See photo of mouldings.)

5 8-foot lengths of "stop" moulding

2 8-foot lengths of 1/2" x 1/2" (or close to this) moulding

1 3-foot by 5-foot piece of hardware cloth, with 1/2" grid

1 3-foot by 4-foot piece of plexiglass, or plastic window 'glass'

1 roll of 3-foot wide 'weed block' fabric; black is preferred

1-pound box of 2 1/2" screws

1-pound box of 1 1/2" screws

1 1/4 inch nails, about 32

thin 1 inch nails, about 8



Cutting list for 4 12-foot lengths of decking planks:

(1) 47 + 47 + 47 inches
(2) 34 + 34 + 28 + 47 inches
(3) 34 + 34 + 47 inches
(4) 34 + 34 + 7 3/4 + 7 3/4 + 12 1/2 + 47 inches

Cutting list for 6 8-foot lengths of decking planks:

(1) 47 + 47 inches
(2) 34 + 34 + 28 inches
(3) 34 + 34 inches
(4) 34 + 34 + 7 3/4 + 7 3/4 + 12 1/2 inches
(5) 47 + 47 inches
(6) 47 + 47 inches

The 7 3/4 and 12 1/2 and 28 inch pieces are cut in half lengthwise.

Mouldings, hardware cloth, and 'weed block' fabric are cut to fit the frames.

About 2 inches is cut off one short side of the plexiglass so that the window overlaps only half of the window frame all around.



Tools - see photos.



Construction (Also see photos):

The six 34-inch pieces and six 47-inch pieces are used to make three frames, 34 by 45 inches inside, and 36 by 47 inches outside. Use three 2 1/2 screws at each corner, but for the top frame, mark where the front (long side) will be cut one inch from the bottom edge. Two of the screws need to be centered in this one inch so that no screws will be cut. Clamp each corner joint in position, drill three holes with a drill matching the solid core of the screw, insert the screws so that the heads sink into the wood a bit, then remove the clamps.

Bottom Frame ---

Ihe hardware cloth is probably in a 3 foot wide roll; you will need to unroll a 4 foot section of it and make it approximately flat. Use 1 1/2 inch nails for the following. Lay the hardware cloth over the bottom frame, and begin by nailing down a 36-inch edge of the hardware cloth on a short edge of the bottom frame. Use only enough nails to hold this edge in place. Then stretch it out to reach the other short edge. Cut the hardware cloth to match the length of the bottom frame (47 inches). Cut three pieces of stop moulding to match the width of the bottom frame (36 inches). Nail one of these pieces over each of the short edges of the bottom frame, anchoring the two ends of the hardware cloth. Nail the third piece of stop moulding over the center, from the center of one long side to the center of the other long side. Now cut four pieces of stop moulding to cover the exposed portions of the two long sides of the bottom frame, and nail these in place. This is the bottom of the bottom frame.

Cut four pieces of the 1/2" x 1/2" (or close to this) moulding to make a rectangular frame that will fit inside the bottom frame with a margin of 1/8" all around. Fasten these pieces with two thin 1-inch nails at each corner. Cut a rectangle of 'weed block' fabric that is about 36 by 47 inches. Stretch this fabric over the frame of moulding and staple it to the outer edge of the moulding. Place this inside the bottom frame with the stretched fabric on the hardware cloth and below the frame of moulding.

Middle Frame ---

You should have four small pieces of planking 7 3/4 inches long, with a width one-half the width of a plank. These 'verticals' will be fastened to the long sides of the middle frame, at the inside corners, protruding one inch above and one inch below the frame. (See photos.) Use three 1 1/2 screws for each vertical. Clamp each vertical in position, drill three holes with a drill matching the solid core of the screw, insert the screws so that the heads sink into the wood a bit, then remove the clamp. With a coarse file, taper the outside edges of the protruding parts of each vertical to make it easier to fit the frames together.

Try stacking the frames. If the fit is too tight, try turning one of the frames around, or turning the middle frame up-side-down. If a better fit is found this way, mark the frames to indicate which sides should be aligned. If the fit is still too tight, use the coarse file to remove some wood from the outside edges of some verticals.

While the top frame is stacked on the middle frame, mark on the bottom rear plank of the top frame the location of the inner edges of the rear verticals of the middle frame. This will help to locate the verticals of the top frame.

Top Frame ---

For the top frame, mark where the front (long side) will be cut one inch from the bottom edge. On each side (short side), mark a straight angled line from the center of the top edge to one inch above the bottom of the front corner. First cut each short side on these lines. Then adjust the tilt of the saw blade to match this angle, and cut the long front side lengthwise one inch from the bottom edge.

Ventilation holes

Cut notches for the ventilation holes in the edges of the rear planks of the top frame that will be facing each other. Each notch is 4 inches wide and 1 inch deep. Mark each edge 10 and 14 inches from each rear inside corner, adjust the saw for 1 inch depth, and cut across each mark. Before cutting out the notches, mark the center of the edge across each notch, at least 1 inch past the notch on either side. Then adjust the (circular) saw depth to 2 1/8 inches, and cut a slit in the center of the edge by dropping the saw blade down on the center line. With a general-purpose saw blade, the cut should be wide enough for the hardware cloth to fit. (For a handheld circular saw, you need to lean the front edge of the saw guide on the plank edge, line it up, turn on the saw, and slowly tilt the saw down to a level position.) The center of the saw blade should land over the center of the notch; but to be sure, slide the saw a little to either side of the estimated center position.

Mark the bottom of each notch one inch from the plank edge. Here are two methods of cutting the bottom of each notch:

(1) With a 1/4 inch drill, make holes along the bottom of the notch, including the corners. The holes should be tangent to the line marking the bottom edge of the notch. Use a chisel to break away most of the wood from the notch area, then finish with a rough, then smoother, file.

(2) With a 1/4 inch drill, make holes only at the corners. With a saber saw, cut the bottom edge of the notch from one hole to the other.

Cut two 3 by 5 inch rectangles of hardware cloth, and cut away the four half-inch corners of each piece, as shown in the photos. Make sure that each piece is as flat as possible.

By now, the slit that was cut across each notch is filled with sawdust. Use one of the hardware cloth pieces to scrape out the sawdust. Now insert a hardware cloth piece in each slit of the larger piece of the top frame. The center of the hardware cloth piece should align with the edge of the plank. Now stack the smaller piece of the top frame on top so that its slits fit over the top half of the hardware cloth pieces.

Verticals

While the top frame was stacked on the middle frame, you marked on the bottom rear plank of the top frame the location of the inner edges of the rear verticals of the middle frame. This will now be used to locate the verticals of the top frame. Make a vertical line at each mark, that is, parallel to the corner of the top frame.

You should have two pieces of planking 12 1/2 inches long, with a width one-half the width of a plank. These are the verticals for the top frame. Place each piece alongside one of the vertical lines that you made, on the side of the line away from the corner. The top of each vertical piece should be 1/2 inch below the top rear edge of the top frame, and the bottom should protrude below the top frame. Clamp in place, then fasten each vertical piece with six 1 1/2 inch screws, three screws into each rear plank, and alternating the positions of the screws toward the left and right sides of the vertical. (Drill holes for the screws as before.)

Each side of the top layer of the top frame is a triangular piece that extends from a rear corner toward the center of one side. Line up each of these pieces with the plank below it, and drill a hole for a 2 1/2 inch screw 4 inches back from the pointed end down through the pointed piece into the plank edge below it. Then, holding the pieces in alignment, fasten with a 2 1/2 inch screw in the predrilled hole, sinking the head of the screw into the wood a little.

Window

Cut pieces of 'stop' moulding to go on the top sloping edge of the top frame. To make mitered corners, cut these to overlap at the corners, and hold in place, overlapped at the corners, with two temporary nails on each piece, about 10 inches away from the corners, and only partly hammered down. With a hacksaw or other fine-toothed saw, cut across each corner on an angle from the outside corner to the inside corner through both overlapping pieces. Remove the cut-off scrap, and the moulding will lie flat with mitered edges at each corner. Remove the temporary nails, and re-nail with 1 1/4 inch nails with about 10-inch spacing all around.

Lay the window plastic sheet on the top frame and position so that two or three edges of the plastic overlap half the width of the border of 'stop' moulding. Mark the remaining one or two edges of the plastic where it should be cut so that all edges of the plastic will overlap half the border of moulding. using a grease pencil or crayon and a straight-edge. Then cut the plastic as marked, with a hacksaw blade.

Cut pieces of 'ply cap' moulding to go on the top edge of the top frame. The thicker edges of the 'ply cap' moulding go toward the outside, the stepped side down and the curved side up. Make mitered corners as for the 'stop' moulding, but don't nail permanently.

Put the plastic window on the top frame, overlapping half the width of the frame of 'stop' moulding all around. Then put the 'ply cap' moulding pieces in place so that the thin inner edges lie on top of the window and the thick outer edges lie on the 'stop' moulding and trap the plastic window in place. Nail with small nails, piercing the 'ply cap' moulding at the step edge where it meets the window edge.

Props ---

Here we describe devices for propping open the cold frame, either a little bit for ventilation, or high enough to reach in and work with the contents.

Cut three lengths of the 1/2" by 1/2" moulding, 6, 10, and 13 inches long. The 1 1/2 inch screws can be used with these, but 1 1/4 inches would be better. Fasten the 12 inch piece centered on the inside of the front wall of the top frame, with two screws, 2 inches from each end of the piece. Drill a hole (for a screw) in the 6-inch piece 2 1/2 inches from one end. Drill a hole in the 10-inch piece 4 1/2 inches from one end. On the inside of the front wall of the middle frame, make two holes 1 1/2 inches down from the top edge and 4 inches from the center to the left and right, that is, 8 inches apart.

Screw the 6 and 10-inch pieces to the middle frame using these holes. With these pieces each fastened with one screw each, they can pivot on the screws. When not used, these pieces are horizontal with the longest arms pointing toward the corners of the frame. But one of the four ends of these pieces can be turned upward to prop open the top frame. Depending on which of the four ends is chosen, the top frame will be propped open 1, 2, 3, or 4 inches for varying amounts of ventilation.

Take one of the 28-inch pieces that are half the width of a plank, and cut a notch in each end. Cut each notch by making two cuts into the end 3/4 inch from each edge, and 3/4 inch deep. Draw a line for the bottom of the notch, from the bottom of one cut to the other. Cut out the bottom of the notch by either of the methods described for the notches use for the rear ventilation holes.

This prop is used to hold the cold frame wide open, for working inside. The notches keep it from slipping off the edges of the top and middle frames. When not used, it can be stored inside the bottom frame alongside the front wall, or alongside a side wall if you prefer that.

If you like, you can fasten a handle to the front edge of the top frame.

Saturday, July 18, 2009

Comparing Technologies

I heard that Wolfram Alpha was finally available, and I wanted to try it out. Wolfram Alpha is designed to be more than a search engine -- it's an answer engine. A search engine tries to find Web documents that contain information you want. But Wolfram Alpha will try to calculate an answer for you from data that it can access.

For example, if you want to know the "weight of the earth in pounds", it figures that (1) by "weight" you really meant mass, (2) the earth mass is available in a table of data about the planets of the solar system (although in metric units), (3) a table of conversion factors is available, and (4) a formula for converting units is available. Moreover, it has the 'smarts' to know that this is the data needed to get the answer, and it knows how to find and combine the details to get the answer.

Now, what problem would I use to try out this new answer engine? Well, I recall reading that DNA is an incredibly dense data storage and retrieval system, but I didn't have any number for the data density in, say, bytes per pound. So, I tried to get the number from Wolfram Alpha. But "DNA in pounds" was not precise enough. How much DNA? Just one 'base pair' (one unit of the chain), or an entire chromosome? And if a chromosome, which kind? (because they have different lengths)

DNA is a chain of information units called nucleotides. The chain is shaped like a twisted ladder, with each rung a pair of nucleotides that encodes two bits of information. There are four kinds of the nucleotides, so I began by asking for the mass of each kind, using their chemical names:

adenine mass in pounds: 4.9468*10-25 lb
guanine mass in pounds: 5.53252*10-25 lb
thymine mass in pounds: 4.51683*10-25 lb
cytosine mass in pounds: 4.06729*10-25 lb

I also needed the mass of the 'backbone' unit, for the 'sides' of the ladder:

deoxyribose mass in pounds: 4.45458*10-25 lb

Then, assuming that the four nucleotide types are used equally, I could now compute the data density of DNA:

1.084547*1024 bytes per pound
(That's about a one followed by 24 zeros.)

Now, what man-made data storage and retrieval system could I compare this to? I have an 8 GB thumb drive that weighs a quarter of an ounce, which may not be the most dense, but it's denser than a DVD or a hard drive. I calculated it's data density to be:

5.5*1011 bytes per pound

That means that DNA is about two trillion times more dense than the thumb drive. That is, the data capacity of a quarter of an ounce of DNA is equal to about two trillion 8 GB thumb drives! Engineers would love to be able to design a data storage and retrieval system with the density of DNA, but they don't know how.

Yet there are atheistic scientists that believe that mindless evolution accidentally created DNA millions of years ago. I have two reactions to this evolutionary belief:

First, as an engineer, I feel insulted that people actually think that a random process can out-do what none of my engineering colleagues can accomplish.

Second, it is clear to me that I don't have enough faith to be an atheist.

Tuesday, June 02, 2009

A Disingenuous Argument

In Steve Mirsky's article An Immodest Proposal in the Opinion section of the June 2009 Scientific American (p. 37), Mirsky quotes from Jonathan Wells' article Darwin's Straw God Argument on the Discovery Institute web site (http://www.discovery.org/a/8101) without the courtesy of naming the article and with the discourtesy of insulting the name of the web site. The quote:

Darwinism depends on the splitting of one species into two, which then diverge and split and diverge and split, over and over again, to produce the branching-tree pattern required by Darwin’s theory. And this sort of speciation has never been observed.

Then, apparently pretending to be ignorant of the fact that most creationists, and Wells in particular, make a distinction between macroevolution and microevolution, Mirsky goes on to waste an entire page of ink to propose that the breeding of dogs is proof that the sort of speciation that created all of the species has indeed been observed.

The first part of Wells' paragraph from which Mirsky quotes reads:

The best way to find “evolution’s smoking gun” would be to observe speciation in action. There actually are some confirmed cases of observed speciation in plants -- all of them due to an increase in the number of chromosomes, or “polyploidy.” But observed cases of speciation by polyploidy are limited to flowering plants, and polyploidy does not produce the major changes required for Darwinian evolution.

Later in Wells' article, he writes:

So although Darwinists believe that all species have descended from a common ancestor through variation and selection, they cannot point to a single observed instance in which even one species has originated in this way. Evolution's smoking gun is still missing, and Dobzhansky’s working assumption that macroevolution equals microevolution remains nothing more than an assumption.

So it is obvious that Wells makes a distinction between macroevolution and microevolution. For the sake of readers not familiar with these terms, I will briefly explain: Microevolution refers to the small genetic changes as observed within the various 'kinds' of life. Macroevolution assumes that larger genetic changes or an accumulation of small genetic changes has produced all the species from a common ancestor. Microevolution postulates many genetic trees, and macroevolution postulates one tree. In both cases, the details of the tree branching are only estimates, and for microevolution the division of 'kinds' is also estimated.

Microevolution, creationists admit, has been observed. (So has the continual breaking of world records. But does that even suggest, let alone prove, that one day athletes will jump across the Hudson River from Nyack to Tarrytown?)

So Mirsky's disingenuous proposal does not disprove Wells' statement. His line of argument needs an observation that breeding of dogs has produced cats or lizards or anything other than more dogs.

Friday, April 17, 2009

Bird Rescue

It began as I was cutting down this spruce tree, which had gotten way too big. I was cutting off the branches, a preliminary to cutting the trunk. As I cut a branch above my head, and the branch began to sag, I heard a fluttering sound, then saw a small bird flutter to the ground and then noticed a nest dangling from the branch, barely attached.


Each branch is a horizontal fan of dense needles, which makes a nice shelf for a nest, but I was unable to see the nest from below. In the photo, you can see the partially cut branch dangling. I climbed down my ladder, and there was a fledgling bird huddled motionlessly on the ground, well camoflaged amidst the debris that typically collects under an evergreen tree. Somehow, my first guess was that it was a mourning dove, which was confirmed later.

When I invited my wife Donna out to see the young bird, she noticed another one nearby. I was relieved that I hadn't stepped on it, and carefully verified that there wasn't a third one. I left a message with a local bird rehabilitator in case professional help was needed, then proceded according to professional advice that I remembered reading.

Both fledglings were remaining motionless, and there was no immediate danger, such as cats, so I fetched a small, shallow, wire basket and two pieces of soft wire, and climbed up the ladder again. I fastened the basket on a nearby limb, and put the nest in the basket. I also cleared out a few twigs above it so that they wouldn't scratch the young birds when I returned them to the nest.

I had to chase each bird a little, because they could flutter and run on the ground a little. But I formed a cage around it with my hands, then gently closed in, folding the wings gently back to the normal resting position, at which point the bird would calm down, Knowing the nest would be on my left, and I would need one hand on the tree for my own safety, I held the bird in my left hand from above before climbing the ladder.

Then I removed all my equipment, knowing that my project would be on hold until these fledglings learned to fly and no longer needed the nest. I had a pile a spruce branches about 60 feer away, where I could keep an eye on the nest while cutting the branches small enough to fill leaf bags. There were some small leafless trees that gave me some cover, but also partly blocked my view of the nest site. Nevertheless, I soon heard the sound that mourning doves make when they fly upward.

Later, I sat waiting at a distance from a different angle where I could see better. From there, I saw two adult mourning doves come to the nest, and one flew away. Now I knew that the parents had found them. The next day, sometimes I would see an adult on the nest when I checked, and sometimes not. Here's a few photos of the nest, taken with a zoom lens. In the last photo, there may be two adult heads. (The fledglings keep their heads tucked in, with no neck showing.)





Once, when the adults were away, I got out the step-ladder again to get a close-up photo of the fledglings, and to verify that both were in the nest. It didn't show the nest contents as clearly as I hoped (next photo).



The step-ladder was standing on its own near the tree, so next I folded it and leaned it against the tree for a closer look. But as I held the camera for this close-up, one fledgling jumped out of the nest and fluttered to the ground, achieving a little more horizontal component of his flight this time. Also, he was a little harder to chase down, so he was noticeably stronger and more ready for real flight.

Just after I caught him, my daughter Susan arrived home, so I asked her to take a photo of the young bird before I returned him to the nest. Note the tucked-in head position and the flight feathers.



Just after I got him back into the nest, I spotted three hawks soaring together overhead. I got him out of sight just in time, I thought. Later, it occurred to me that hawks don't normally hunt in groups. A young hawk or two must have been out on a training exercise.

Saturday, February 21, 2009

The Genetic Code - how to read the DNA record

(NOTE: The end of this article has been revised and expanded from the original.)

DNA is the kind of molecule that stores genetic information in every living cell. It describes how our bodies are made, and to a degree, how they operate. The translation of DNA, a sequence of nucleotides, to a sequence of amino acids (protein units) is a complex but fascinating process. Here's a simplified account of the essentials:

A selected portion of the DNA is copied in complementary form, making a messenger RNA (mRNA) chain molecule. There are four kinds of nucleotide in the DNA, abbreviated G, T, A, and C; and four kinds in the RNA, called C, A, U, and G. When copying from DNA to RNA, the correspondence is:

G -> C
T -> A
A -> U
C -> G

So, for example the DNA sequence

GTACCATG..

when copied to RNA, makes the RNA sequence

CAUGGUAC..

A sequence of three nucleotides, such as GCC, is called a codon. Each codon sequence encodes for one of 20 amino acids, or else is a stop codon. The genetic code is a scheme that translates the 64 (4 x 4 x 4) types of codon to the 20 amino acids and the stop signal. The codon for the amino acid Methionine also functions as a start signal. There are three codons that mean 'stop', and there are one to six codons representing each amino acid. Here's the complete genetic code:

[START], Methionine <-- AUG
Alanine <-------- GCU, GCC, GCA, GCG
Leucine <-------- UUA, UUG, CUU, CUC, CUA, CUG
Arginine <------- CGU, CGC, CGA, CGG, AGA, AGG
Lysine <--------- AAA, AAG
Asparagine <----- AAU, AAC
Aspartic acid <-- GAU, GAC
Phenylalanine <-- UUU, UUC
Cysteine <------- UGU, UGC
Proline <-------- CCU, CCC, CCA, CCG
Glutamine <------ CAA, CAG
Serine <--------- UCU, UCC, UCA, UCG, AGU, AGC
Glutamic acid <-- GAA, GAG
Threonine <------ ACU, ACC, ACA, ACG
Glycine <-------- GGU, GGC, GGA, GGG
Tryptophan <----- UGG
Histidine <------ CAU, CAC
Tyrosine <------- UAU, UAC
Isoleucine <----- AUU, AUC, AUA
Valine <--------- GUU, GUC, GUA, GUG
[STOP] <--------- UAG, UGA, UAA

The key elements of translation are small transfer RNA (tRNA) molecules. Each kind of tRNA molecule has a region called the anticodon that can recognize and attach to a particular codon of a messenger RNA (mRNA) molecule. The tRNA molecule has another region called the "3' terminal" that attaches to a particular amino acid. This attachment is aided by molecules called aminoacyl-tRNA synthetases, of which there is generally one kind for each kind of amino acid. There are even helper molecules that provide a proofreading function to detect and correct any translation errors.

Each kind of tRNA molecule associates one kind (sometimes a few kinds) of codon with a particular amino acid, so there are one or more kinds of tRNA for each row of the above genetic code table. For example, there is a kind of tRNA with a region that attaches to Tryptophan (with the help of a specific kind of aminoacyl-tRNA synthetase), and with another region that recognizes and attaches to any part of mRNA with a UGC codon.

So if the RNA sequence is

AUGUUCUUAUACUCCUAG

we can divide it into codons as

AUG UUC UUA UAC UCC UAG

Five tRNA molecules will attach to the first five codons, and five amino acids will attach to the tRNA molecules, something like this (with abbreviated names for the amino acids):



No tRNA molecule will attach to the last codon, because it is a stop codon, and the translation will stop.

The amino acids connect into a chain in this sequence, like this, which detach from the tRNA molecules:

Met-Phe-Leu-Tyr-Ser

Each tRNA molecule detaches from the mRNA and from the chain of amino acids, to be 'loaded' with another amino acid and used again. The detached chain of amino acids, a protein, folds into a three-dimensional shape to function as a protein. (This folding is another complex process, often needing the aid of specialized helper molecules.)

These are the basics of the translation, but it is actually more complex than this, because other molecular machinery is needed to make everything happen in the right sequence. The 'work bench' of the mRNA reading machinery is a collection of tiny particles called ribosomes that look like tiny dots in the center of a living cell (but huge compared to the tRNA molecules). There are also other tools such as initiation factors, releasing factors, and various enzymes that control the process.

Each ribosome has a small and large unit that link together on either side of the mRNA ribbon, forming a bead that can slide along the mRNA, reading it. Many ribosomes typically read one mRNA strand at one time, producing proteins. Each ribosome has three sites on one side of the hole through the 'bead' that hold tRNA molecules in position to attach to, and detach from, the mRNA as it passes through the hole. The ribosome 'workbench' has other sites to hold the various other 'tools' in position to operate on the various stages of the process.

Where does the genetic code come from? It is not the result of chemistry or any laws of physics. It is determined by the set of tRNA molecule types, and aminoacyl-tRNA synthetase types, which are constructed according to DNA information, which encodes not only the building materials and the building plans, but also the building tools and the building methods. In other words, the genetic code is just information that has always been there since life began.

The number of possible genetic codes is a huge number, 85 digits long:

1,510,109,515,792,918,244,116,781,339,315,785,081,841,294, 607,960,614,956,302,330,123,544,242,628,820,336,640,000

and all of these many codes would work equally well. But all of life uses just one genetic code, about 280 bits of information, the one that scientists Watson and Crick discovered in 1953, but was there since creation. The theory of evolution has no explanation for how the genetic code began, because it can't explain how information can arise from no information. Nor can it explain why there is only one genetic code (out of such a huge number of equally workable codes), even though there is extreme variation of everything else. The mechanism of the present genetic code is very complex; and evolutionary theory supposes that it randomly evolved from a simpler, smaller code. But because there are so many equally viable genetic codes, random evolution should have produced species with many different codes. The evolutionary explanation is far more unlikely than dumping a bucketful of dice on the floor and expecting them to all land with the same number up.

The creationist explanation is that the universal genetic code is like a signature of the creator, who chose a uniform code for all of the designs of life. A short story will illustrate the principle:

During the Cold War, Russia was suspected of stealing American technology. Proof came when some Russian war equipment given to a third country was captured and examined. It contained an integrated circuit that was identical to an American design. It is theoretically possible that the Russians had the same design concept, leading to a similar design. But digital circuits have thousands of component parts connected by thousands of wires. There trillions of ways to position the parts on the chip and trillions of ways to route the connecting wires that work equally well. It would be impossible for the Russians to independantly produce the same positions and routings even if the logical design were identical. But examination showed the details were identical, even details left over from correcting wiring errors. In effect, there was an American 'signature' in the copied design.