Homemade Capacitors

Capacitors, the electronics textbooks would have you believe, are very simple devices. In their most basic form, they consist of two conductive surfaces separated by a thin dielectric (insulating) material.

Various different materials have been used over the years, from air to paper to tantalum and many more. One popular choice for dielectric material is mica (which is also used for heatsink insulators, since it conducts heat but not electric current.)

“Mica” capacitors have been made using metal deposition for decades at this point — the capacitors are much more reliable and stable this way — but the original mica capacitors from the early 1900s were simply pieces of mica clamped between two metal plates.

I don’t have the necessary equipment to attempt metal deposition, but old-school clamped mica capacitors don’t require very much in the way of equipment. The secret ingredient, of course, is the mica. While on vacation in Maine last month, I came across a large specimen for sale that looked like it might produce nice, clean sheets.

A chunk of mica, as it might be found in nature. (Click for larger.)

This is one of the nicest pieces I’ve seen. I don’t feel too bad about experimenting with it, though. The reason mica works so well as a dielectric is that the individual sheets are extremely thin — so very little is needed. (Single sheets from this one seem to be about 20-30um in thickness, although this is on the edge of what I can measure reliably with digital calipers.)

30um thickness, to something like one sig fig or so…

Using a razor blade and some patience, I was able to lift a layer of mica from the chunk. I then cut it to a roughly rectangular shape. Next, I made a template from an old business card that was slightly smaller than the piece of mica. I used this template to cut two pieces of aluminum foil, making sure they were slightly smaller than the piece of mica.

A single layer of mica (more or less). Click for larger.

The next step was to sandwich it all together. I used more pieces of business card to insulate the outside, allowing the use of alligator clips to clip on to the mica. I then connected the jumper cables to a component tester.

The inner part of the sandwich. The two metal plates must not touch.

The verdict: It works! The component tester shows a capacitor of roughly 80pF (and shows no component when one of the wires is disconnected at the cap.) The capacitance doubles to ~160pF when I hold on to the paper insulation — and almost quadruples again, increasing to nearly 600pF, when I squeeze it together. Time to 3D print a compression jig!

It works!

After printing a simple compression frame, the capacitor ended up at about 214pF. This is less than when I was holding the leads — but it’s more consistent and a lot more reliable this way, even with a very simple frame.

A working, 220pF-ish capacitor.

Strips of metal, interleaved with sheets of mica, might help it get up into the nF range. But that’s a project for another day.


Posted in 3D Printing, Analog, Components, Electronics, HOW-TO, Mad Science, Science, Uncategorized | Tagged , , | Leave a comment


Engineering gets easier every year because of all of the amazing tools that become available. Years ago, if you wanted to do a good physics-based simulation, that meant months of development work and probably several headache-inducing conversations with specialists about forces, free-body diagrams, vector calculus, and other topics.

Today, modern physics simulations exist for little or no cost* — and they’re getting easier to use all the time. I’ve recently started working with Unity — a development environment primarily aimed at game development, but which has many generally useful capabilities.

Most importantly for my purposes, Unity has an excellent, easy-to-use physics simulation package built in. Here is a video of a quick demo I wrote in the course of an evening while teaching myself the basics of Unity.

Such a simulation requires an insane amount of computing power. For each block generated (Unity generates a new one with each video frame), forces from each collision must be calculated and applied to the relevant objects. Simply modeling one cube falling while not perpendicular to the table would be challenging enough — you would need to calculate the time and position of first impact, adjust the time of the simulation accordingly, and predict forwards from that until the next collision.

Fortunately, Unity makes all of that very easy (for the programmer). With a few lines of code, objects are instantiated and set into motion. The built-in collision detection and physics routines and the 3D renderer handle the rest.

Here is the code to generate a brick. This command is automatically called at the start of every frame:

Instantiate(Brick, new Vector3(8 * Random.value - 4, 10, 
8 * Random.value - 4), Quaternion.identity);

This code instantiates (creates a working copy of) a Brick object, at 10 units above the table and somewhere from (-4-,4) and (4,4) on the X/Z plane. So each frame, a brick will appear above the table within four units left-right and within four units forwards-backwards from the origin point at the center of the table.

From here, Unity’s magic takes over. A few more lines assign the size and color of the brick and give it a random 3D rotation. From there, the physics engine handles things completely automatically.

A “cull” script does remove any objects which fall off the table, to keep the overall number of objects limited to a finite number.

Next stop, powered hinge joints and robotics simulations!



* Unity has a very friendly pricing model — completely free for individual use and organizations under $100k in funding or annual income; $25/month for hobbyists and small businesses, and $125/month for larger ones.

Posted in C, Coding, Games, Tools | Leave a comment

Artifact-Free Metrology!

With today’s vote in Versailles, we will soon have a consistent measurement system that isn’t based on a chunk of metal kept in a vault in Paris. Because modern experiments have made it possible to determine the value of universal constants like Planck’s Constant to extremely high precision, the members of the General Conference on Weights and Measures were able to confidently vote to switch us to a new definition of the kilogram — one based on setting Planck’s Constant to an arbitrary value based on careful measurement, and redefining the kilogram based on that.

The International Prototype Kilogram (IPK), or “Le Grand K.” (Image credit: BIPM)

Measuring h to this accuracy involved two different types of experiments, to not only allow for replication but independent confirmation of results using a different method. When two such dissimilar experiments agree with high precision on anything, you’re on the right track. In this case, the results of sensitive Watt-balance measurements were compared with the results of measuring the mass of nearly perfect spheres of a single isotope of silicon to high accuracy. These spheres are probably the most geometrically perfect things anyone has ever made.

With this new definition, set to officially take effect on May 20, 2019, the accepted standard values for several SI values will change very slightly. For most practical purposes, though, this change will be so small as to be lost in the noise. That’s the reason for taking such pains to measure h as closely as possible — we want the new definition to match the old, artifact-based one as closely as possible (since that’s what everyone’s devices are already calibrated to.)

What does this mean? If you love science and like to see it done right, this is an amazing step in the right direction. Going forward, all of the SI units will be defined in terms of natural physical constants that anyone can measure.

Veritasium, not surprisingly, has a great explanation video.

If you’re worried about the measurements changing, don’t be — unless you work with precision measured in parts per billion. It’s a good time for Le Grand K to retire. It will no doubt find a place of honor in a museum — as a 1.0 kilogram mass that used to be the 1.0 kilogram mass.

Because having to explain that your definition of the kilogram is losing weight is more than a little embarrassing.

Posted in Current Events, Digital Citizenship, Electronics, Fundamentals, Mechanical, Science | Leave a comment

Resurrecting the Sinclair

The first computer I ever used was a university mainframe, accessed through a teletype terminal in my uncle’s apartment. It played a mean game of Tic-Tac-Toe (and presumably helped with my uncle’s Finance dissertation.)

The second computer I ever used, the first one I ever owned, and the one on which I learned all kinds of horrible 1980s-BASIC programming habits on, was a Timex-Sinclair 1000.

The Timex-Sinclair 1000. (Thanks, Mom and Dad. Best present ever!)

The TS1000 had the distinction of being the first home computer under the magical $100 mark. While still not cheap, that put it within reach of normal people. The Personal Computer revolution was beginning!

The TS1000 is based on the deservedly popular Z80 microprocessor. Sinclair Research combined the Z80 with a custom video card, a ROM containing the BASIC programming language, and 2KB of RAM.

The Timex-Sinclair 1000 system board.

The keyboard no doubt contributed to the low cost of the Sinclair, as it was a very cheaply manufactured membrane keyboard which connected through a slit in the top case to plug onto the system board. These worked marginally well for a few years, but would inevitably become brittle with age. When this happened, the conductors would develop hairline cracks. If even one of the thirteen keyboard lines broke completely, a whole section of the keyboard would become unresponsive. It’s rare to see one working these days. Neither of my two did…

My original keyboard, showing the deteriorated connector.

Not only did these old keyboard connectors break — they would often break off in the connector, requiring exploratory surgery to clear them out before the connector could be inspected, cut cleanly before the break, and hopefully reinserted if it hadn’t become too short.

That’s not supposed to be there. Not without the rest of it, anyway.
Fortunately, it came right out.

Nostalgia being what it is, many of my fellow middle-age geeks fondly remember the Sinclair, keyboard problems and all. So I guess it’s not surprising that someone came up with a solution. I found a site selling replacement ZX81/TS1000 keyboards for about $15 or so. Not a bad price at all to resurrect an old (if temperamental) friend!

The new keyboard.

A few weeks later, the keyboard arrived. The key action is much better than the original, but the tinned metal connectors on the end appear to be intended for soldering rather than for plugging into the keyboard connector.

Tinned wire connections on the new keyboard. Good for soldering, not so good for staying in the old socket.

Never one to design an engineered solution when a perfectly good hack would do, I cut up a wire-wrap socket (probably half as expensive as the keyboard — they’re Not Cheap). It’s not going anywhere, now.

A hacked-up wire-wrap socket works perfectly.

With the new keyboard, the Sinclair is back from the dead! Now to fix up the case a bit and work on some peripherals — or at least a way to save and load programs from an mp3 player or something.

It’s alive! (And so is the 1970 Ford TV that I used to use with it.)


Posted in BASIC, Nostalgia | Leave a comment