Video 1. Open Circuits book interview by CuriousMarc (2022) Source.
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:
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 behaviour 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. Source.
Video 1. Finding Capacitance with an Oscilloscope by Jacob Watts (2020) Source. Good experiment.
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:
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.
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.
Figure 1. Source.
Figure 1. Source.