by Ciro Santilli (@cirosantilli, 34)
Figure 1.
White bra cup size C
. Source.
Ciro Santilli is a fan of this late 2010's buzzword.
It basically came about because of the endless stream of useless software startups made since the 2000's by one or two people with no investments with the continued increase in computers and Internet speeds until the great wall was reached.
Deep tech means not one of those. More specifically, it means technologies that require significant investment in expensive materials and laboratory equipment to progress, such as molecular biology technologies and quantum computing.
And it basically comes down to technologies that wrestle with the fundamental laws of physics rather than software data wrangling.
Computers are of course limited by the laws of physics, but those are much hidden by several layers of indirection.
Full visibility, and full control, make computer tasks be tasks that eventually always work out more or less as expected.
The same does not hold true when real Physics is involved.
Physics is brutal.
To start with, you can't even see your system very clearly, and often doing so requires altering its behaviour.
For example, in molecular biology, most great discoveries are made after some new technique is made to be able to observe smaller things.
But you often have to kill your cells to make those observations, which makes it very hard to understand how they work dynamically.
What we would really want would be to track every single protein as it goes about inside the cell. But that is likely an impossible dream.
The same for the brain. If we had observations of every neuron, how long would it take to understand it? Not long, people are really good at reverse engineering things when there is enough information available to do so, see also science is the reverse engineering of nature.
Then, even when you start to see the system, you might have a very hard time controlling it, because it is so fragile. This is basically the case of quantum computing in 2020.
It is for those reasons that deep tech is so exciting.
The next big things will come from deep tech. Failure is always a possibility, and you can't know before you try.
But that's also why its so fun to dare.
Stuff that Ciro Santilli considers "deep tech" as of 2020:
Applications of power, we have to remember it is there to notice how awesome it is!
  • lightning
  • motors
  • sending nad receiving communication signals
  • computers, which in turn can do computations and improved communication
Figure 1.
GPHS-RTG diagram
. Source.
Video 1.
The Soviet Union's Deadly Abandoned Nuclear Generators by Andy Mcloone
. Source.
Figure 1.
GPHS-RTG diagram
. Source.
Figure 2.
Cassini probe's RTG before installation
. Source.
Most promising approaches as of 2020:
Video 1.
Why Private Billions Are Flowing Into Fusion by Bloomberg (2022)
Source.
  • Joint European Torus
  • General Fusion: compress with liquid metal. Intends to demo in JET site.
  • Helion Energy: direct fusion to electricity conversion without steam, direct from magnetic field movements
  • First Light: shoot microscopic objct at a target to crush it so much that fusion happens
It is interesting that there are several different approaches to the problem. This feels a bit like quantum computing's development at the same time, increases hope that at least one will work.
Once again, relies on superconductivity to reach insane magnetic fields. Superconductivity is just so important.
Ciro Santilli saw a good presentation about it once circa 2020, it seems that the main difficulty of the time was turbulence messing things up. They have some nice simulations with cross section pictures e.g. at: www.eurekalert.org/news-releases/937941.
Video 1.
Inside JET: The world's biggest nuclear fusion experiment by Wired UK (2020)
Source.
Video 1.
How NIF Works by LLNL
. Source.
Operated by a hand crank.
Figure 1. Source.
Figure 1. Source.
Figure 2. Source.
Figure 1. Source.
Figure 2. Source.
This notation is designed to be relatively easy to write. This is achieved by not drawing ultra complex ASCII art boxes of every component. It would be slightly more readable if we did that, but prioritizing the writer here.
Two wires are only joined if + is given. E.g. the following two wires are not joined: 
  |
--|--
  |
but the following are: 
  |
--+--
  |
Simple symmetric components:
  • -, + and |: wire
  • AC: AC source. Parameters:
    • Hz: frequency
    • V: peak voltage
    e.g.: 
    AC_1Hz_2V
    If only one side is given, the other is assumed to be at a ground G.
  • C: capacitor
  • G: ground. Often used together with DC, e.g.: 
    DC_10---R_10---G
    means applying a voltage of 10 V across a 10 Ohm resistor, which would lead to a current of 1 A
  • L: inductor
  • MICROPHONE. As a multi-letter symmetric component, you can connect the two wires anywhere, e.g. 
    ---MICROPHONE---
    or: 
    |
MICROPHONE
    |
  • SPEAKER
  • R: resistor
  • SQUID: SQUID device
  • X: Josephson junction
Asymmetric components have multiple letters indicating different ports. The capital letter indicates the device, and lower case letters the ports. The wires then go into the ports:
  • D: diode
    • a: anode (where electrons can come in from)
    • c: cathode
    Sample usage in a circuit: 
    --aDc--
    Can also be used vertically like aany other circuit: 
    |
a
D
c
|
    We can also change the port order, the device is still the same due to capital D: 
    --cDa--

 |
Dac--

 |
Dca--

   |
--caD
  • DC DC source. Ports:
    • p: positive
    • n: negative
    E.g. a 10 V source with a 10 Ohm resistor would be: 
    +---pDC_10_n---+
|              |
+----R_10------+
    If only one side is given, the other is assumed to be at a the ground G. We can also omit p and m in that case and assume that p is the one used, e.g. the above would be equivalent to: 
    DC_10---R_10---G
    If the voltage is not given, it is assumed to be a potentiometer.
  • T: transistor. The ports are sgTd:
    • s: source
    • g: gate
    • d: gate
    Sample usage in a circuit: 
    ---+
   |
--sgTd--
    All the following are also equivalent: 
       |
   g
--sTd--

    |
--Tsgd--
   |
  • I: electric current source. Ports:
    • s: electron source
    • d: electron destination
  • V: Voltmeter. Ports:
    • p: positive
    • n: negative
    If we don't need to specify explicit positive and negative sides, we can just use: 
    ---V---
    without any ports. This is notably often the case for AC circuits.
    Optionaly, we can also add the sides as in:
Numbers characterizing components are put just next to each component with an underscore. When there is only one parameter, standard units are assumed, e.g.: 
+-----+
|     |
C_1p  R_2k
|     |
+-----+
means:
  • a capacitor with 1 pico Faraday
  • a resistor with 2 k Ohms
Micro is denoted as u.
Wires can just freely come in and out of specs of a component, they are then just connected to the component, e.g.: 
DC_10---R_10---G
means applying a voltage of 10 V across a 10 Ohm resistor, which would lead to a current of 1 A
If a component has more than two parameters, units are used to distinguish them when possible, e.g.: 
AC_1kV_2MHz
means an AC source with:
Video 1.
Open Circuits book interview by CuriousMarc (2022)
Source.
One more more electrical wires surrounded by an insulator.
Video 1. Source. Cat 5e cable stripped
Main implementations: the same as electronic switches: vacuum tubes in the past, and transistors in the second half of the 20th century.
Video 1.
How to make an LM386 audio amplifier circuit by Afrotechmods (2017)
Source. Builds the circuit on a breadboard from minimal components, including one discrete transistor. Then plays music from phone through headset cables into a speaker.
The fundamental intuition about capacitors is that they never let electrons through.
They can only absorb electrons up to a certain point, but then the pushback becomes too strong, and current stops.
Therefore, they cannot conduct direct current long term.
For alternating current however, things are different, because in alternating current, electrons are just jiggling back and forward a little bit around a center point. So you can send alternating current power across a capacitor.
The key equation that relates Voltage to electric current in the capacitor is:
(1)
So if a voltage Heavyside step function is applied what happens is:
  • the capacitor fills up instantly with an infinite current
  • the current then stops instantly
More realistically, one may consider the behavior or the series RC circuit to see what happens without infinities when a capacitor is involved as in the step response of the series RC circuit.
Figure 1.
Electronic symbol of a capacitor
. Source.
Video 1.
Finding capacitance with an oscilloscope by Jacob Watts (2020)
Source. Good experiment.
Video 2.
Capacitors Explained by The Engineering Mindset
. Source. 2019.
Figure 1. Source.
This is what happens when you apply a step voltage to a series RC circuit: TODO graph.
Ideally can be thought of as a one-way ticket gate that only lets electrons go in one direction with zero resistance! Real devices do have imperfections however, so there is some resistance.
First they were made out of vacuum tubes, but later semiconductor diodes were invented and became much more widespread.
Figure 1.
I-V curve of a diode
. Source. This image shows well how the diode is only an approximation of the ideal one way device. Notably, there is this non-ideal voltage drop across the device, which can be modelled as constant. It is however an exponential in fact.
Video 1.
Diodes Explained by The Engineering Mindset (2020)
Source. Good video:
The first diodes. These were apparently incredibly unreliable, especially for portable radios, as you had to randomly search for the best contact point you could find in a random polycrystalline material!!
And also quality was highly dependant on where the material was sourced from as that affected the impurities present in the material. Later this was understood to be an issue of doping.
It was so unreliable that vacuum tube diodes overtook them in many applications, even though crystal detectors are actually semiconductor diodes, which eventually won over!
For a long time, before artificial semiconductors kicked in, people just didn't know the underlying physical working principle of these detectors. What I cannot create, I do not understand basically.
This was the first generation of commercially successful radios.
It uses a crystal detector as its diode, which is a crucial element of the radio, thus its name.
They were superseded by transistor radios, which were much more reliable, portable and could amplify the signal received.
Figure 1. Source.
Video 1.
How a Crystal radio Works by RimstarOrg
. Source.
GPIO generally only supports discrete outputs.
But for some types of hardware, like LEDs and some motors, the system has some inertia, and if you switch on and off fast enough, you get a result similar to having an intermediate voltage.
So with pulse width modulation we can fake analog output from digital output in a good enough manner.
Notably used to connect:
You can buy large sets of them in combitation of male/male, male/female, female/female. Male/male is perhaps the most important
Video 1.
Making Jumper Wires by PCBurn! (2018)
Source.
These often come pre-soldered on devboards, e.g. and allow for easy access to GPIO pins. E.g. they're present on the Raspberry Pi 2.
Why would someone ever sell a devboard without them pre-soldered!
Figure 1.
6x1 pin header
. Source.
Figure 2.
Underside of a Raspberry Pi 2
. Source. At the top of this image we can clearly see how the usually pre-soldered pin header connectors go through the PCB and are soldered on both sides.
Allows you to connect two adjacent pins of a pin header. Sometimes used as a hardware configuration interface!
Figure 1. Source.
Something where DC voltage comes in, and a periodic voltage comes out.
Video 1.
Oscillators: RC, LC, Crystal by GreatScott! (2015)
Source. Good video. Contains actual breadboard experiments on oscilloscope and circuit diagrams
Oscillator made of an LC circuit.
Video 1.
From Raw Crystal to Crystal oscillator
. Source. by United States Army Signal Corps (1943)
Video 1.
How LEDs work by VirtualBrain
. Source. 2021. Good 3d schematics clearly explaining part of the LED electronic package.
Video 1.
How are LED Chips and LED Encapsulation is made by Future Linear
. Source. Starts from some level of cut square chips. Still in round wafer form.
www.reddit.com/r/Optics/comments/18f6bdt/comment/kcsiook/ mentions:
LEDs are broadband by nature, since the spontaneous emission broadly speaking reflects the overlap of the Fermi distribution and the density of states
Direct and indirect band gaps is an important part of why diodes don't emit light apparently.
Apparently fundamentally LEDs in principle work as photodetectors, but
Figure 1.
Hand drawn schematic of the magnetic field induced in a magnetic core by an electromagnetic coil
. Source.
Although transistors were revolutionary, it is fun to note that they were just "way cheaper and more reliable and smaller" versions of exactly the main functions that a vacuum tube could achieve
The first working one in 1947 by John Bardeen and walter Brattain in Bell Labs Murray Hill.
People had already patented a lot of stuff before without being able to make them work. Nonsense.
As the name suggests, this is not very sturdy, and was quickly replaced by bipolar junction transistor.
As of 2020, not used anymore in logic gates, but still used in amplifiers.
Figure 1. Source.

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