Saturday, July 18, 2020

Bonsai Lightning!

We live in a residential space - there are limits to exactly what magnitude of lightning we can tolerate in the kitchen, after all. Why not make a dwarf kind of lightning?

I recently ran across a $9 miniature Tesla Coil kit. It seemed too good to be true, but it works (there were a few missing or helpful but absent parts: a nut for the screw to hold the transistor to the heat sink, and a hot glue gun really helps!).

This is not a link that generates any kickbacks or credits, I include it for those who are interested:

My son and I assembled the kit in about an hour (teaching the whole way, and making several repairs to self-inflicted damage to a few parts along the way). It worked on the first try when we were done, so I rate this as a decent design.

Key notes:

1. The secondary coil has a tendency to unwind - a drop of hot glue at each end of the winding saved a lot of rewinding time.

2. The high voltage end of the secondary (the little wire sticking up in air) is literally a tiny strand of copper wire. We hot glued it to a plastic drinking straw that we anchored on the inside of the coil to give it some stability.

3. Solder bridges are easy to make when soldering parts into the circuit board - especially if your assistant is enthusiastic with the solder.

4. Always solder in an area with good ventilation and wash hands after!

5. Put something underneath your soldering area that cannot catch fire - we used some fiberglass fabric (just the glass fabric!).

6. You need a 12V DC power supply that can provide at least 400ma of current, which they do mention but I repeat it here since we forgot.

My son says "The Tesla Coil is a complex circuit, but one of the easiest circuits to assemble. If your parent's say it is ok to build a Tesla Coil by Nikolai Tesla, fire up your soldering iron and get a 12 Volt power supply. Don't use a one-cell battery holder, since it does not work. When things don't work, it is not exciting. If you do have to happen to have a 12V power supply and everything you need in the kit, you can build it."

The lightning that is generated is small and at a very high frequency - the primary frequency of the oscillator appears to be around 200ns, or 5 MHz.

This is a frequency where the electricity will not penetrate deeply into human skin - however - lots of things can change that, so really no touching the high voltage end of the coil!

At 5MHz the skin depth is only about two micrometers, which is enough to be felt and cause pain - though the bigger danger is burns. There is enough power in the output to cause thermal burns from your skin heating up in the area of the spark, which is the more likely injury mode.

Also be aware that this device is a hazard to some electronics if they get too close - smart watches and cell phones come to mind.

Saturday, July 11, 2020

Why are there more lizards along trails in the late afternoon?

Recently we noticed that lizards are often much more abundant in the late afternoon actually on and along trails in the chaparral than in other areas. That brings up the question "Why?".

Turns out you just have to look at the trail the right way and it is obvious - though in this case, "the right way" is a literal type of camera reference - a thermographic camera. The photo above was taken with infrared light (or "IR" for short) between 7 and 14 microns in wavelength, instead of the more typical photos which use light roughly between 0.4 and 0.8 microns in wavelength.

The scene above might look more familiar in ordinary visible light (this isn't exactly the same spot, since the IR photo was taken just after sunset - it does show how the trail is flanked by vegetation and it is nearly the same spot).

Why use such odd light? Because it is the light that we humans give off, as well as pretty much anything else that is near "body temperature". Lizards are generally "cold blooded", which means that to get to their ideal comfort temperature, they have to move into warmer or cooler spots to adjust their temperature. In the heat of the day, they are looking for cooler spots - at least when it as hot as some parts of California get in summer...

Turns out their preferred body temperature is very close to ours (a bit cooler, not much though).

The trail remains warm as the day starts to cool off in the late afternoon and long into the evening. The lizards come to soak up the heat and be more comfortable.

Wait, "the light that humans give off"???

Yes, we all emit light. Lots of it, in fact. It is light that we cannot see with our eyes, but with other sensors we have - try holding the underside of your forearm facing someone else on a cool day and see if you can "feel" the infrared they emit from a few feet away. It is subtle, and most of us can notice it once we start looking. 

Planck's Law of Blackbody Radiation states that the amount of power emitted by and object effectively through thermal means (meaning atoms are vibrating and colliding, which causes the emission of photons at all wavelengths, very roughly) relates to the temperature of the object according to this relationship:

Three of the constants that define this universe are in the equation - I grabbed it from the Wikipedia page.

Astronomers, photographers, and interior decorators all know this to some degree, in the sense that a hotter star appears bluer than its cooler neighbors. "Red Dwarf" stars are cooler than our yellow sun, while Blue Giants are hotter. If you want a "warm" color of light, you go to cooler, redder equivalent filament temperatures (at least that was the case when light bulbs were actual bulbs with actual tungsten filaments...).

Let's look at what the equation above predicts for the light that our Sun gives off versus what we emit.

I had to put the green curve on a separate scale from the blue, red, and yellow curves since the power emitted by people as deep infrared light is really tiny compared to what the sun emits (the red or 5700 Kelvin curve).

The fact that we emit our own light is what makes thermal imaging possible. The slight differences between different areas of our bodies translate to significant changes in the power output by those areas.

I can literally call my son the "light of my life". Of course, that applies even more to the soup he is about to enjoy.... perhaps I should avoid working in the greeting card industry...

The soup is hotter in places than anything else in the photo, even though the "white hot" areas are just about 100 degrees Fahrenheit. His forehead and neck are hotter than his shirt or hair - so they give off more light. It just happens to be light that we cannot see with our eyes.

Friday, July 10, 2020

Father-Son Trekking

We go exploring and discovering together. It doesn't have to be some grand celebrated destination like Yosemite - this old cracked and decommissioned road in the suburbs of Los Angeles leads through a world with hundreds of plant species you can see in a single afternoon, lots of lizards, snakes, bugs, birds, bats, and even some terrestrial mammals. It is 12 minutes from Downtown Los Angeles.

There is a cartoon I ran across on that captures one aspect of this that is fun:

There is much more to this. I value our wild places, even the scraps lost in the edges of a great city.

Things tell stories. They speak in languages we do not speak and cannot speak, languages that are open for us to hear if we have patience. I'm not telling this to my son, I am showing him and living this experience with him.

If I look at a hillside, it is a book I can partially read. There is a story about great geological forces and deep time, about how the rocks there were made, and then how they got to where they are, and finally how they came to be visible, even if no actual rocks are evident. Plants have roots that reach into the soil, into the rocks below the surface, and will tell you bits about what they find. You have to know the plants and what their likes and dislikes are, and if you invest in that, they will tell you things that are plain to see, if you look the right way.

Even in something as "simple" as sporting events, the game is richer if you know who the players are and what they are known for.

I bet most of you can find the Blainville's Horned Lizard in this photo. Finding them out like this is not exactly rare, if it is a less common delight than I wish it were.

Can you find the one in the next photo?

Or this one?

That last one is more typical of what we find - a trace, a track, especially since the ones of these that live longest tend to be the wariest of dogs, people, and such.

This stuff is best lived, shown, done together.

We eat wild berries, Miner's Lettuce, and wild mushrooms (our rule: all mushrooms must be cooked before being eaten, and only Dad is allowed to cook them - I am a Botanist but even that is not enough, I joined my local mycological society - see - and did what is the only sane way to learn edible mushrooms that I am aware of - apprentice with other folks that really know what can and cannot be eaten - then do it again if you are in a new area or ecology). We catch lizards (and release). I've taught my son how to catch dragonflies with his bare hands (hint: there is a lot of standing motionless involved...).

My son's prized things include a pineapple plant, a miniature Aroid from the Mediterranean that he seeks, but does not yet have (he is learning how to plan and save and prepare), a linear power supply he soldered together that works, his fans, and his portable seed cleaner. He invents and explores and tries things. He fails and we celebrate and then figure out what we learned and how we might do better with the next attempt.

He finds Calochortus in seed and stalk faster than I do, and has for some time. He knows how and where to find the elusive wild cherries of California.

It all starts by going for a walk together, in a place where we are both just details. To meet and exchange I find it easiest in places that are not my world, not his world, but our world. Listening is easiest where it is quiet.

Wednesday, July 8, 2020

A Tale of Two Soils

Meet Lupinus microcarpus variety densiflorus! This California native is part of a species group that can be found all the way from Canada to Argentina. Even better, it is easy and fast to grow, since in the wild it is an annual - a plant that must grow from seed to flower and to mature seeds again in a season or two, and which dies and exists only as seeds in the ground for part of the year.

This year I thought I would help them grow even faster by planting them in a vegetable garden type of potting soil. That produced unexpected and bad results - growing them in a mineral poor, low nitrogen, fast draining soil make awesome plants, while growing them in rich garden soil results in simply not growing them. Why?

This is a tale of the right soil, the wrong soil, and how to tell which is which for a given plant.

We grow a lot of desert and California native plants. A lot of these are specialists in odd, highly inorganic soils, such as serpentine soils. Lupinus microcarpus var. densiflorus is not terribly fussy about soils, being found all the way from Canada to Argentina. What it demands is a well aerated soil.

Below are some of our seedlings in two very different soils. The square pot at the top shows a healthy seedling. The yellowing seedlings in the lower trough are not at all happy. These are growing side-by-side. Why the droopy yellow leaves on the lower plants?

The poor health of the lower plants is a direct result of the soil. It is a commercial potting soil (for containers). Tomatoes grow well in it, as do our parsley, nasturtiums, peppers, and beans. This species does not.

The sickly plants have brown roots. Healthy roots are almost always, at least when small, white. This is true for this annual Lupine - when we unpotted the plant shown above to examine it's roots, here is what we found:

This is the species planted in our "desert bulb mix", which is 3 parts Pearlite, 1 part silver 80 grit blasting sand, and 3 parts rehydrated coir (like peat moss, but sustainable)(parts are measured by volume here). Water drains quickly through it, there are low levels of nutrients, and it is very difficult to turn it sour or make it go anaerobic. Notice the long, white roots visible at the bottom center. These pots are 3" square and 7" deep for scale. This is a textbook healthy and happy young plant.

When we unpotted the others in the trough, we found completely different roots.

These roots are shorter and very brown. They are fighting for their life. Notice how dark the soil is and how it sticks to the starter pot. Compare the texture of this soil with the soil above.

This soil is almost pure compost as purchased - we added most of the sand and whatever pearlite it contains. Vegetables grow fantastically well in this stuff, desert plants are not as fond. Key things to notice - there are fewer air spaces, and a lot of fine grained organic material that forms a sticky "mud" for lack of a more concise term.

The effect of the soil on the plant is dramatic. Soils are not a one-size-fits-all affair. Watch the plant - we have read to some of our plants from various garden books, and it appears many plants are illiterate. They will, however, communicate clearly when they are happy and when they are not. Listen to the plant, take guidance from a book, but if the plant and book differ, then listen to the plant!

These are some photos of the species in the wild this year in California. Notice that this is a sandy soil, yet one that has a very low organic material content and a coarse, aerated structure.

Friday, July 3, 2020

Building Seed Cleaning Machines - Seed Differential Sedimentation

Ever have a fistful of seeds and chaff and sticks from some random wild species and all you want is just the clean seeds?

Sound familiar?

Then you need a Seed Cleaning Machine! Problem is, most of the ones you can buy were designed for specific crops, such as "grains" or corn or such. If you do get lucky and find a highly adjustable type suitable for wild seeds, they are likely the sort where there is a big tube and a screen, and in the process of cleaning the seeds you blow chaff all over the general area - and you still cannot separate seeds from heavier debris.

After building seed cleaning machines based on winnowing or fanning machine designs for the past several decades, I decided we could do better.

Here was my list of objectives:
  • Separate seeds from everything else
  • No adjustments needed
  • Kid friendly
  • Easy to build
  • Captures all the chaff without making a mess!
  • Insensitive to batch size
How to accomplish this list? Applied Physics! The path a feather takes on a windy day and the path of a stone are very different. Let's make use of that observation and build a machine.

In the chart above, the three forces on the seed are drawn. They do not balance, so the seed accelerates along a path. For simplicity, here are the terms in the equations above - two equations are aerodynamic drag, and one is acceleration due to gravity:
  • Fg is the force the seed experiences due to gravity
  • Fa is the force the seed experiences due to the horizontal flowing air
  • Fz is the force the seed experiences due to falling through the air
  • A is the cross-sectional area of the seed, in square meters
  • Cd is the coefficient of drag, generally 0.4 to 2.0, lower numbers are for smooth shapes, higher numbers are for angular or rough shapes
  • Vz is the speed of the seed falling through air, in meters per second
  • Vx is the difference between the horizontal airflow speed and the horizontal speed of the seed
  • p is the density of air, generally around 1.2kg per cubic meter at sea level
  • m is the mass of the seed, in kilograms (a small number!)
  • g is the acceleration due to gravity at planet surface, about 9.8 meters per second squared
Putting the equations above into a spreadsheet and running small time steps (0.02 second) for a 1mm x 2mm seed weighing 40mg each and for air flowing from the right at 1.0 meters per second creates this path for the falling seed:

Heavier seeds fall more vertically, while lighter seeds of the same size will fall at an even shallower angle than shown.

This is all theoretical. What happens in real life?

This is a batch of seeds for Fritillaria agrestis, a wonderful plant that has become moderately rare since it liked to grow in places that are now largely farms or cities in the Central Valley, among other locations. The heavy seeds are covering a small range of bins on the right, while chaff and unfilled seed coats (bad seeds) are spread out on the left. I would call this a good separation.

This is a batch of an onion-like plant named Dichelostemma capitatum, once again with a good separation quality. The input is vertically above the rightmost cup in each case.

The machine we built to do this is basically two slabs of Foam Core Board, separated by a 2cm wide gap. A computer fan is connected to a tetrahedral duct on the right side to provide a smooth sheet of flowing air to the airgap between the slabs, and the seeds are added via a funnel on the upper right.

We are using the linear power supply from my oldest surviving seed cleaner on the right edge of the photo (likely topic of a later post) to control the speed of the fan, with the collector cups separated by short vertical popsicle sticks in the base of the unit. Under the device the collecting cups sit, with a fresh tray of them shown in the lower left. The structure on the left will have to be part of another post, as it feeds into our Vortex Chaff Collector.

It took an hour or two to get all this together once we thought out the design. We are making more and better variants, since this is a lot of fun - hot glue guns, cutting, soldering - all stuff that gradeschool kids can help with.

Happy Seed Cleaning!