Home-brew Spectrometer

Due to a quality control problem at a local marijuana dispensary, we found the high-CBD plants we thought we had actually were unknowns.  This became apparent when the plants got big enough to exhibit their typical growth habit and odor (smell can vary widely among different clone types).  To make it clear:  we want high CBD for pain management.  Not interested in getting high.

Via online searching I found a chemical test for CBD and it showed that just one of the 3 clones contained much CBD -- but, unfortunately, the test is not very quantitative.  It relies on the development of a purple color when the plant material is added to a 5% solution of sodium hydroxide dissolved in alcohol.   The darker the color, the more CBD is present.  But eyeballing is not very accurate.  I started thinking that a spectrometer might improve the accuracy of the test.  In addition to the alcohol-hydroxide test, there is a very sensitive test that will stain THC and CBD slightly different colors.  It is a dye called Fast Blue B, dissolved in water, and is used to develop thin layer chromatography (TLC) plates.  So it MIGHT be possible to determine the ratio of THC and CBD by using Fast Blue B and a spectrometer to resolve the different colors.

But commercial spectrometers are expensive.  Sure, it is possible to find them for less money on Ebay:  but often they need software and a computer, and if the package is complete the price goes up.  The other aspect of this work is to hopefully make it possible for others to do the same measurements on their own material, so a one-off purchase from ebay won't cut it.   As an alternative I found an open-source spectrometer here.  Cost is around $50.  For that you get a web cam, an optical slit, a CD-R disk (to turn into a diffraction grating), a black cardboard box and materials to assemble it all.  I put the thing together and found it wasn't mechanically stable enough to generate repeatable absorption spectrograms.  So I used the essential parts -- the camera and slit -- and built my own spectrometer.  The photos below show the spectrometer I put together.

Exterior showing the slit and lid.  The "hinge" is a length of adhesive-backed aluminum (which is opaque to light).

This is a photo showing the "optical holder" design.  It is a block of oak with a flat-bottomed hole just large and deep enough to glue in a super magnet.  The bottom of the spectrometer is a steel plate, so the blocks stay put -- but are easy to move around to optimize the optical path.

And here is a photo of the interior.  The diffraction grating is glued to one of the optical blocks.  I sawed a slit in the block to provide a robust mounting point for the grating.  The web cam is attached to an optical block using heavy-duty double-sticky tape.  The corners of the enclosure are reinforced with wood blocks that were glued in place.  The top, sides, and ends of the box are made using foam-core poster board.  Black, of course.  I also put a length of the poster board on the bottom, to reduce reflections that would degrade contrast of the spectrum.  I had some black silicone caulk so I ran a bead along the front corners and along the bottom edges as well, to reduce light leaks.

And here is the spectrum of a CFL lamp, obtained using my spectrometer:

Unfortunately, I found the web camera is not compatible with the Public Labs spectrometer software.  At least, not on my linux laptop.  So I found it necessary to write my own program(s) to do the job.  I found a starting point here but it has a fairly serious memory management problem -- it acquires a bunch of frames, and only then performes averaging.  I modified the code to acquire one video frame, then extract ONE line of interest for processing.  This way I can average over any number of frames without running out of memory.  I also wrote a version to get the calibration factors needed to convert pixel positions to wavelengths.  The end result is a system that easily resolves the two green emission lines around 540 nanometers, and has a low noise level in the data.

Now I can move on to testing my THC/CBD measurement idea....

Update

A lot has happened since my last post.  Some highlights:

I have a new hip joint.  The joint on my right side was bone-on-bone, painful enough to restrict my activities.  The surgery went quite well -- I was out of hospital the same day of the procedure!  And right now I'm pretty much back to normal as far as muscle strength in that leg.

Another interesting project:  our old barn.  Two winters ago we had a fairly heavy snow fall, and the weight was enough to cause one of the walls to buckle.  Not much of a foundation, especially after many years of dry rot.  Fortunately the wall just dropped a few feet before finding a new equilibrium, and the rest of the barn was flexible enough to not shatter.  It just looks pretty bent.  I am in the process of rebuilding the wall.  I am jacking up that side using some harbor freight "farm jacks".  The temporary support header is several feet over from the old wall, so, once the barn is back to square (more or less) I will install new concrete footers and a new wall.  I will post some photos when I have a chance.

The garden is our perennial summer project, and like previous summers it took a lot of time.  I'm just glad I was in good enough condition so we could get the garden in.  We did have some help putting in some things, like the cucumber and bean trellises -- thanks to Mike and Debbie for that!  However, I wasn't quite in good enough shape to mulch the garden like I usually do, and we paid the price -- weeds galore.  And perhaps that is why our peppers and tomatoes didn't do as well this year as previous years.  Even so, we got enough tomatoes to put up 40 pounds of tomato-vegetable juice and 20 pounds of pasta sauce.

Another milestone:  we initiated a quarterly "draw" from our investments, to cover expenses.  Up to that point we were funding our expenses from savings in the bank accounts.  I have tracked our burn rate so had a pretty good idea on what we would need on a quarterly basis.

Garden Goodies

Here are a couple of photos showing some of our garden produce.

The top photo is a bowl-full of Aji Limon peppers.  They are spicy with a fair amount of "sneaker heat", and, in addition to the yellow color, they actually do have a nice citrus-like flavor.  I turned these into a fermented brined-pepper mash.  Very tasty, and a good way to preserve garden produce for the winter.

The second photo shows the winter squash we got this year.  There are several varieties shown here:  Cinderella pumpkin (the large orange guys), Kuru (small orange), Buttercup (small dark green), Sweet Meat (medium-sized gray-green), Butternut (oblong tan fruits), and Queensland Blue (medium sized gray-green, ribbed).  The Kuru and Queensland Blue were new to us this year.  We like the Kuru -- we put it in a batch of Mussaman Curry last night.  The Queensland Blue is very hard and dense, but the flavor is not as good as the others.  Our overall favorite winter squash:  Sweet Meat.  Best keeper:  Butternut.

Rocking Toy Part 2

Summer activities -- gardening, playing, etc. have delayed part 2 of my rocking toy post.  We're canning tomato juice right now, which involves some basic hanging around to do the hot water bath -- so I have some "spare" time to do part 2.

In part 1 I explained the basic principle of a pendulum or other simple mechanical oscillators.  My first photo shows the can opener that first got my attention:

 It's a simple old-fashioned "church key" with a punch on one end and a crown cap remover on the other.  In the context of a rocking toy, the opener rocks on the point of the punch and the arc of the cap remover.

 The above photo shows the church key with some added weights -- a stack of small neodymium magnets.  The idea was to raise the overall center of gravity so it was closer to the center of rotation.  This in turn would reduce the oscillation frequency, which it did -- the new oscillation frequency was about 1 hertz.

And now, my version of the rocking toy.  The main piece is about the same length.  I drilled and tapped a hole on the left for the pivot, which is a bolt whose end was formed into a taper using my lathe.  The right side has an arc machined into it, using my milling machine and rotary table.  I smoothed the arc with some 220 grit wet/dry sandpaper.  I also needed to bend the right-hand end down, to replicate the church key.  To make sure the bend was exactly perpendicular to the long axis of the bar, I cut a slot (again, with my mill) from the top to bottom of the bar.  It is about halfway through the bar.  Then I put it in a vise and bent it until it was about the same angle as the church key.

The end result is a mechanical oscillator that, again, has a surprisingly low frequency -- although for some reason as yet undetermined, my version oscillates at a slightly higher frequency.  Anyway, it is a fun "twiddler" to play around with.

If I was going to make another one, I would use cold-rolled steel instead -- it has a much nicer finish.  And refine the corners on the left side so it has a more refined appearance.  But those are just aesthetics.

First food post

Something that should be clear by now is we have a broad range of interests.  That includes food.  My wife and I have a 1600 square foot vegetable garden.  In some years we have extracted about 1,000 pounds of winter squash from it, in addition to quarts of tomato sauce, myriad zucchini, peppers, cucumbers, leaf vegetables, beets, basil, and on and on.

But we've been aging cheese, as well.  A well-aged Tillamook cheddar can  beat just about any other cheese, and, if you have the space in your 'fridge (or a separate refrigerated cheese vault), you can enjoy some really flavorful cheese for a very cost.  We have aged cheddar, in its original wrapper, for well over 10 years.   The acid level of the cheese, plus the salt content, does a good job of preserving it.  And the aging process produces lots of flavor components (like glutemates) that really ratchet up the flavor.

As an experiment, we bought a 2 pound brick of Tillamook "colby" cheese awhile back.  It is a milder sorta-cheddar/jack cheese.  But the price was right, and we had the space to store it awhile.  Well, that aging time turned into 15 years (!).  We rediscovered it, observed some potential issues, so decided to open the package and taste it.  Well, it is just fine -- some might say terrific.  Because this style of cheese often has some added red pigment, it looks a little odd --pink-- but it tastes great.  By the way, a well-aged Tillamook that has absorbed some truffle flavor from some Oregon white truffles, is amazing.

The main issue with preserved food is either the hydration level (think jerkey on the good side) or acid.  If the acid level produces a pH level of 4.3 or lower, clostridium botuliun can't grow, so the food is safe to consume.  Not to say it's tasty, that depends on other fermentation parameters.  Fermentation is not just about beer or wine, it helps make sauerkraut, kimchi, pickles, and artisan sausages.  It converts part of the food product to (typically) lactic acid.  Acids reduce the pH of food, and most putrefying bacteria don't like low pH.  So they are more stable.

Fermentations like this are used to produce (as mentioned above), sauerkraut, pickles, kimchi and sausages.  It also is used to make bread, cider vinegar, wine, beer, sake, miso, soy sauce, fish sauce, and many other foods found across the world.  In most cases, the fermented foods have more nutritional benefits than the original input biomass.  This it not an opinion.  Additional nutritional benefits are well documented.

Just say'in.

An unusual cooling system idea

Sorry, no drawings or photos in this post.  Brain work only.

In warm seasons like this one, my thoughts sometimes turn to DIY air conditioning (AC).  In our climate, AC is one of those rarely-needed things so buying some off-the-shelf solution doesn't appear to be a very cost effective solution.  I'd much rather spend lots more time and less money on something that works well enough to take the edge off the heat when it occasionally occurs.  I've seen approaches using evaporative cooling, but our climate also has an additional challenge -- relatively high humidity.  So-called "swamp coolers" work best in regions where the relative humidity is low.  They're more efficient, and the added moisture to the air is welcome.  On the other hand, when you start with 60% relative humidity, the cooling action isn't as good:  and the increased humidity due to the swamp cooler can actually make you LESS comfortable, even if the temperature is slightly lower.

There are indirect cooling approaches where a heat exchanger comes into play, cooling inside air without adding moisture.  The heat exchanger is an added complexity, and also has its own impact on efficiency.  What if we could start with much-cooler water, cooler than can be achieved using evaporative cooling?  If we can get that, perhaps we can live with less-than-perfect heat exchanger technology.

There may be a way to do this.

Long ago I performed an experiment to see if it would be possible to make my own turbomolecular vacuum pump (I refer you to Google to get educated on this type of vacuum pump). I mounted two thin mylar plastic disks on an axle. They were spaced a few tenths of an inch apart. Then I spun them up, using either a Dremel tool or an electric drill (this WAS a long time ago so I don’t remember that part all that clearly). Centrifugal force would pull the disks into flat planes, but, if some pumping action were taking place, the space between the disks would be at a lower pressure so the disks would be pushed together. I observed that the disks were indeed pushed toward each other so some pumping action was going on. I could not increase the speed enough to get the disks to touch, due to instability and vibration problems, but this problem probably could be solved with some refinement.

If the axle was made from a tube, and we drilled some holes in it between the two disks, it is likely that some sort of pumping action would occur that would pull gas down the tube toward the disks: but now we’re faced with making a good rotary seal. The angular velocity of the tube would be less than the outer edges of the disks, but it still is a nontrivial problem if you want a reliable vacuum pump.

So that approach languished for a long time. But I recently had an idea where the scheme could still be useful. As a chiller. In point of fact, it would function as a single-pass refrigeration system. In this approach, the spinning tube is dipped into a water reservoir. The tube also has a restrictor to reduce the water flow so the water doesn’t completely fill the pump. If the water does fill the pump, I believe the water probably will boil in the disk portion of the pump and screw up the cooling cycle (see below). If sufficient vacuum is developed the water will boil, extracting heat from its surroundings. The water vapor is ejected by the spinning disk pump, where it immediately re-condenses (and liberates the heat it absorbed when it boiled).

In its simplest form, the rotating tube would be submerged in the water so the expansion of liquid water into water vapor would cool the water on the immediate exterior of the tube, which could then be circulated into a secondary heat exchanger. Efficiency could be improved by increasing the surface area of the submerged tube, perhaps with aluminum or copper disks (but they can’t be too large or frictional forces would limit the maximum RPM, and also heat the water).

The advantage of this method is that the minimum-achievable temperature is not determined by the relative humidity of air, unlike a standard evaporative air conditioner. The minimum temperature would be the freezing point of water (0C/32F).

NOTE: this scheme could be foiled by the buildup of minerals from the water feedstock, since the minerals would be concentrated by the liquid-vapor conversion.  Some type of purge or ballast-water approach would be needed for a commercially viable system.

Also NOTE: while one might think the water vapor exiting the pump would be cold & therefore useful for cooling purposes, in fact it will re-condense as soon as its pressure returns to room pressure. When this happens, it will release the heat it absorbed.  Now, of course, the water will be very finely dispersed and some to all of it will evaporate in the ambient air – again cooling down in the process. But there won’t be any “gain” offered by the pump, and the ultimate minimum-low temperature will be determined by the dew point of the ambient air – much higher than the freezing point of water.

So it appears the energy input of the spinning-disk scheme is best used as a way to implement a single-pass refrigeration system.  I use the term "single-pass" because the input fluid, water, is available without any special condensor.  Unlike a classic closed-system refrigeration system.

 

Rockin' out, part 1. An observation and pendulum theory.

Some time back I was playing with an old-fashioned bottle opener, commonly known as a "church key".  At one point I placed the opener down so the rounded and pointed ends were facing down, touching the counter top (polished granite).  Here's a photo of the opener:

  When I put the opener down, I noticed it rocked back and forth surprisingly slowly.  Intrigued, I looked more closely at what was going on.  I saw that the opener rocked back & forth across the curved end, and in that configuration the opener was pretty stable.  It would eventually tip over if pushed over too far.

And then I tried an experiment to see if I could further increase the period of this simple mechanical oscillator.  We have some small (~1/8" square) super-magnets that are used to hold photos, coupons etc. on our refrigerator.  I stacked several of them together to raise the overall center of mass of the system, and put the stack on the opener.  Sure enough, the opener rocked even more slowly.  See below (sorry, no videos yet):

I was able to increase the period to about 1/2 second/cycle, pretty amazing considering the relatively small size and mass of the system.  Due to the relatively poor finish on the rounded end of the opener, it rocked in an irregular fashion.

I started thinking about making an "improved" version of this,  for a fun little machining project.  I did finally make one, with one false start.   But at this point, rather than just showing what I did I want to start by explaining the physics behind the mechanical oscillator, and what determines its frequency.   I will start with the pendulum, as shown below (two different positions of the sphere are shown).

The sphere is hanging on a cord of "R" length.  So what causes the sphere to swing back & forth?  Take a look at the right-hand drawing of the pendulum.  The sphere has moved over, and, due to the fact that the cord is a constant length, the sphere rises slightly.  Since the force of gravity always points down but the cord is at an angle, a restoring force appears which opposes the deflection of the sphere (this assumes that the forces due to gravity and acceleration are transmitted along the cord at angle "w").  In a dynamic situation the system exhibits a periodic transfer of energy between potential energy (due to the lift "H") and kinetic energy.  What determines the oscillation frequency?  If the cord is lengthened, for a given angle "W" "H" becomes smaller, and the restoring force becomes less.  The effect is to slow the pendulum oscillations down.  If we increase the mass, the acceleration decreases due to the relationship F = Ma where M is the mass of the sphere and a is the acceleration.  Solving for acceleration:  a = F/M.  Therefore the mass accelerates more slowly under the influence of the restoring force.  So frequency also decreases as mass increases.

Another way to look at the pendulum is as a system with a center of mass that is constrained to move around a given radius of curvature.  In these terms, the oscillating bottle opener is a similar type of mechanical oscillator.  Increasing the mass (by putting magnets on top of the the opener) decreased the oscillation frequency, just as it does for a pendulum.  We could continue to add mass until the center of mass is above the center of radius.  At that point the system would become unstable and flop over.  Unlike a pendulum.

Next time:  some implementation considerations with my rocking toy.