A little bit about light

I’ve been giving myself a crash course refresher on light over the last new months. It started when I picked up a used Laser Cutter and wanted to figure out how it cuts with light. What I’ve written here is my understanding of things. I may be wrong, if so, please let me know in the comments.

My simplification of a CO2 laser is that it’s a poorly designed Neon light that gets way too hot and produces a heat ray that we can manipulate with mirrors to vaporize things. Magnifying lens on a sunny day style. I fear if I ever find an ant in my laser cutter whatever project I was working on will be a total loss as I will be chasing the ant with my laser beam. https://en.wikipedia.org/wiki/Carbon_dioxide_laser

So I now have this really sharp cut thing that I can’t see the blade on. A CO2 laser beam is invisible. If you see a red dot on a laser cutter, that is a separate cat-toy style red laser put in place so we can guess about where the actual invisible laser will do it’s thing.

Deep Infrared thermal image of laser cutting fabric
The heat line produced by laser cutting some fabric in a laser cutter
laser cutting fabric
The laser cut fabric. You can see where it has cut the fabric using focused invisible light.

My laser cutter’s light is 9.4-10.6 micron wavelength. This is the same wavelength that Humans glow in the dark. Well, everything room temperature glows at this light frequency or ‘color’.

Deep Infrared

A thermal camera can see light in this ‘Deep Infrared’ zone. I have a Seek Thermal camera that plugs into my cell phone which allows me to see effectively heat. I can walk around and find things that are plugged in that are doing a bad job of being off, and give off heat because they are still on. I can tell the temperature of anything, just by looking at it with my cell phone. I can also look for things that are supposed to help keep me warm and are failing at their job like doors and windows.

A Deep Infrared image of a Kurig Coffee Machine
A Kurig Coffee Machine that wasn’t told to ‘power save’. It’s been heating up since it was plugged in.

Except nothing is ever that simple. Materials have a property called ‘emissivity’. This is how well they emit light at a certain wavelength. Things that emit light well, tend to absorb light well. Things that don’t emit well tend to be reflective in nature.

Humans have a pretty high emissivity about .98 (with 1 being perfectly emissive and 0 being perfectly not-emissive) so we need clothes to stay warm as we would glow all of our heat away without them. But because we are highly emissive, we can absorb heat well too, so this is why you can feel heat being given off by things like hot pans, light bulbs, and turtle heat lamps, and sitting in a sunny spot.

You can see here that I glow. My clothes hold in some of my heat and my glasses block the Deep Infrared light.
You can see here that I glow. My clothes hold in some of my heat and my glasses block the Deep Infrared light.

Things such as shiny metals have a low emissivity, so they tend to reflect heat like a mirror. This is how camping space blankets work. The thermal ‘glow’ that us humans have gets reflected back at us. We absorb a lot of this reflected heat, so space blankets feel warm to us. Because, you know, science and stuff.

But, what this means, is that my fancy thermal camera can’t take accurate temperatures of shiny metal things. What I am really taking the temperature of is the things reflected on these ‘heat mirrors’. To do a good job using thermal imaging for temperature reading the more expensive equipment has material tables that you can assign to spots that have a lookup to a emissivity table so it can calculate the proper temperature based on what it sees.

I am going to carry some electrical tape which has a pretty high emissivity number around .96 and just stick that on things I want a proper temperature of. Because, you know, lazy and stuff.

Materials have some pretty funny ideas about what is ‘clear’ and what is ‘opaque’ at wavelengths other than what we can see with our eyes. Thin plastic bags that we can’t see through are transparent to deep infrared. Stick your hand in a bag, you can see your fingers as clearly as if the bag wasn’t there. Windows, glasses, things that we see through all the time are as black as night to thermal. “Low E” windows are not only black to thermal, they are reflective as well, so you can see your heat reflection in a ‘good’ modern window. CLICK. OH, that’s why “Low E” windows are better, they reflect heat. I get it now.

Near Infrared

Another portion of light, called Near Infrared, has some interesting properties as well. First off, things that aren’t metallic (reflective) are rather transparent. Things look kinda like jello at these wavelengths, the light can see into them a ways. A couple of centimeters often times.

The Near Infrared has another interesting ability. Oils, fats, sugars, alcohols, and proteins absorb certain frequencies of light – they have colors (for lack of a better word) in this range. Click here to Geek Out on Near Infrared. This means that a camera that uses Near Infrared is very useful around the house. We can look at something, and judging by it’s ‘color’ in Near Infrared, we can make a good guess as to what is made of, or at least major components of it. We can’t see near infrared, so we tend not to manipulate the colors in that range.

There is a gadget that takes advantage of these useful properties. The SCiO which is a Near Infrared ‘scanner’.

This little device is even cooler than the thermal camera. It’s small, and can tell you the interesting bits about your food like how many calories and of what type (fats, carbs, protein) are in it. You don’t have to guess at a restaurant if you are tracking your diet anymore.

This doesn’t work like a camera, it is instead a spectrograph. It doesn’t take a picture of stuff, it instead looks at all the colors that are present like how a prism works. You scan something with a SCiO and it breaks apart the intensities/brightness of different wavelengths of light (those would be the colors if this was visible light) and looks up what it sees against a database of stuff that it knows about and when it finds a match, tells you what it is looking at.
If we were to present only pure substances it would be able to tell us what things are easily. However, we don’t have much of anything that is truly pure. Table salt, sugar, baking soda, for the most part tap water are about all I can think of commonly around the house. Most of the stuff we interact with is made up of a variety of things.

This is where we get clever with the SCiO. Instead of needing to extract out the stuff into individual bits (imaging taking a baked cake and separate it back out to it’s flour, sugar, eggs, milk, water, etc) we just capture what a thing looks like in different bits of Near Infrared light and correlate it to things we’ve told the SCiO what they are previously.

The thing that makes this work is that we LIMIT THE DOMAIN of what things are so the SCiO has a chance at making a reasonable guess. For example, there are a lot of things that are Red. Lego, fancy cars, strawberries, some apples, etc. If we showed you a particular shade of red, and asked you what was that color, you can come up with a lot of wrong answers that are that exact shade of red. But if we said we have a berry that is this particular color, you would be able to tell very easily what it is most of the time. Especially if you can look back against other color samples and compare what you have now with what you have seen in the past.

So for the SCiO to work well, we need to train it. We get together a bunch of things that we want to tell apart if it’s not properly labeled. We then teach the SCiO this thing is X, that thing is Y. We can than ask SCiO what is this stuff, it’s something that belongs to this group that we trained it on.

An example could be clear liquids. Clean water, vodka, strong vodka, watered down vodka, rubbing alcohol, denatured alcohol, clear soda, vinegar. These things all look similar to our eyes. They will all look different from each other in Near Infrared. We can train the SCiO about all of these clear liquids, and when we find a glass of one and we don’t know what it is, we can check with the SCiO.

Amazing!

There are some ways in which the SCiO can fail.

  • Shiny mirror like surfaces tend to reflect all light, regardless of the wavelength. Metals for example. We also see this in Visible light as well as Deep Infrared.
  • Things that are black – they absorb light – tend to absorb all frequencies of light including Near Infrared. Things that have been colored black will likely be black to the SCiO as well, and it can’t get a good read on them.
  • Only the major components of something can be read by a SCiO. If there isn’t enough of something to make a strong ‘color’ influence, it simply can’t be read. A SCiO can ‘see’ stuff that is more than 1% or so of the overall item.

 

Understanding how a fancy new tool works ‘under the hood’ helps me manage my expectations of what the tool can and can’t do well. I can ‘hack around the edges’ of it’s capabilities because I understand what the edges of capabilities are and why they exist.

2nd layout of the Mobile Science Lab

I added more items to the Mobile Science Lab.  The main new item is a WeatherFlow WEATHERmeter. This is a pretty neat bluetooth device that captures wind speed and direction, temperature, humidity, and barometric pressure.

layout of pieces for the Mobile Science Lab
The Mobile Science Lab in the middle with the new WeatherFlow WEATHERmeter to the left along with a USB drive that works with cell phones. The new layout is on the right.

New stuff means I needed to update the case.  I fiddled a bit to get everything to fit.  I think the next iteration will end up including layers.  I will need to find some laser safe foam core or something light like that.  The cardboard won’t hold up all that well when there are removable sections.

trying to make cell phone accessories fit into a cell phone drybox
An initial cut of the new layout on some old cardboard that is scarred up from the laser cutter. I think it looks pretty neat this way.

I ordered a much larger Pelican case tonight. The SCiO I am ordering at the end of the week should fit into the new case.

I’ve also added some NFC stickers a few places to make using the bits a little easier. The case has my contact info embedded in it.  The WEATHERmeter is now set up to just tap the phone against it and the correct App will load.

cell phone accessories in a waterproof cell phone case.
The new layout is a lot more full than the previous version. You can see one of the NFC stickers on the lower left corner.

I recently picked up a Seek Thermal camera which plugs into my cell phone and allows…

I recently picked up a Seek Thermal camera which plugs into my cell phone and allows me to see temperatures of stuff. It's a cheap unit, so it doesn't have the built in calibration tables that the expensive 'real' test equipment has. But it's good enough for most people's needs in a non-technical use.

I am reading all up on emissivity, and the science of how it works. Because this influences my usage of my laser cutter, and blacksmithing and even cooking and anything that relies on heat.

So I decided I am going to make a Mobile Science set. Mobile is dual usage, one, it's portable, two it's centered around my mobile phone.

My phone has a lot of sensors and capabilities already.

The Seek Thermal camera gives the phone another super power.

I also want to add a Consumer Physics SCiO https://www.consumerphysics.com/myscio/ which is a molecular identifier. I've wanted this thing since they ran it on kickstarter several years ago. I have actually seen it work in person and absolutely love what it can do. I think it will turn out to be a disruptive technology. This item will be the primary tool in my Mobile Science lab once I get one.

To compliment these two IR different sensors, I want an assortment of basic hand tools that will facilitate in preparing materials for the phone accessories.

I will be working with botany and geology. Also a bit of chemistry.

Optics is a pretty natural option too, given the camera on the phone. I will be making some bead lens microscope adapters for the cell phone camera. A spectrograph as well.

I also found a phone accessory weather sensor that I will be picking up.

I made up a cardboard tray on my laser cutter to organize the few bits I have gathered already. These are fitting in a waterproof cell phone case. I am looking for a waterproof tablet case.

My goal is to have a solid Science Lab the size of a Science textbook. I will likely carry this set about anywhere I go.

I am crazy excited about this idea.

In album 2/22/17

Years ago I had dubbed my rubber mallet "sudo !!"

I've acquired more hammers since, and very recently a laser cutter.

So I've engraved "sudo !!" on my newer rubber mallet that my kids gave me. I also named a small machinist hammer "Subtle Persuasion".

Totally loving the ability to permanently label my stuff with such ease that I don't have time to consider if I ought to.

In album 12/17/16

Things for Leatherworking

I have a friend that is trying to learn 120 things in 20 years.  Well, one of those internet friends whom I will never meet in real life. He mentioned that he was thinking about learning Leatherworking as a thing so I thought I would give a primer on the subject. Not that I am an expert or anything. Sometimes starting is the hardest part, and not knowing what to start with is a lot of the reason to not start.

My half done leather messenger bag.

A good intro into all the words used in leatherworking can be found at https://www.tandyleather.com/en/leather-buying-guide.html.

Leather is sold by weight. Weight per square foot in ounces. The thicker the leather, the heavier the leather, the larger the number. There are charts out there there that will approximate the weight to the thickness to the scale of 1 oz equals 1/64th of an inch. Or thereabouts.

Thicker leather is used for different things than thinner leather. Next time you have something made out of leather, feel the thickness of the leather. Think about why that thickness of leather was used.

There are different ways they make leather – chrome tanned or veg tanned. This is different ways that it is made, different chemistry. I would imagine that there are different strengths and weaknesses for each type, but I don’t know the details. I get whatever is cheapest at the time.

Once you find your leather, you will also need a few things to get started. A cut thing, a stitch thing, likely a few hole things, marking things, and possibly a hit thing.

Cut things are pretty important. I see a lot of videos where people use a disposable razor knife, which seems to work well. They sell expensive half circle knives, which look like they work really well. I’ve made one, but have yet to try it on leather. I use a rotary cutter and like it.

Stitch things are really important. I use two types of needles. Harness Needles and Glovers Needles. Harness needles are not really sharp and are good for going through existing holes. They tend to be used two at a time, one on each end of the thread. You end up making a stitch that looks like a sewing machine stitch, but is much better. The stitches this way don’t unravel easily if cut like from a machine. Glovers needles are wicked sharp and are used on thinner leather like it is cloth. The two threads I’ve tried are the waxed thread and artificial senew. I like the waxed thread better.

There are lots of ways to make holes. The hole things are the second expensive thing to buy, after the leather. You can use them to make little holes to stitch in and you can make not so little but still small holes to put rivets and snaps into. The simplest hole tool is the awl. This makes small holes. I’ve found that some awls are better than others. Long, thin, well tapered and smoothed awls like a needle work better than cheaper awls with a simple angled ground tip like a nail. I’ve not tried making one yet, but I have a few broken drill bits I may give a try to grind. You can get round hole punches which are handy. The kind that looks like a punch and needs a mallet is fussy to use, but can be used to make holes that aren’t near an edge of the leather. The type that looks like a pinwheel crossed with a paper punch is easier to use, but only works near the edges of the leather. My favorite hole tool is the stitching punches. These are the most expensive, but singularly made my work look better. I didn’t skimp on these, getting the nicer set available at the store. Getting nice even stitches is a huge improvement on the niceness of the finished product.

Nice stitching punches.

Mark things help layout and measuring and stuff. I find ball point pens work well. In woodworking, they say if you want to make a line, use a pencil, if you want a fine line, use a sharp pencil, if you want a perfect cut, use a knife. I do a lot of marking with my knife, but I prefer using an awl – it leaves a good mark but doesn’t cut the surface weakening the leather. I picked up a cheap divider (looks like the old geometry class compass) and use it for marking stitch lines along the edges of the leather. This trick with the stitching punches is what made my work go from a total hack job to not bad.

I use a simple stick as my hit thing. Why buy something that I found in my yard?

A stick found in the yard works as a mallet.

I’ve done a bit of reading, and a lot of youtube watching to learn how to do a bit of leatherworking. It’s hard at first to sort out who knows what they are talking about and who’s not any better than I am. Once you find a good youtube author, give ’em a subscribe so you can keep getting more of the better videos.