Ciro Santilli Main implementations: the same as electronic switches: vacuum tubes in the past, and transistors in the second half of the 20th century.
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: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.
- the capacitor fills up instantly with an infinite current
- the current then stops instantly
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.
- youtu.be/Fwj_d3uO5g8?t=153 how it works
- youtu.be/Fwj_d3uO5g8?t=514 applications:
- protection against accidental battery inversion
- rectifiers, notably mentions a diode bridge
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:
- pin headers
- breadboard holes
You can buy large sets of them in combitation of male/male, male/female, female/female. Male/male is perhaps the most important
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!
Allows you to connect two adjacent pins of a pin header. Sometimes used as a hardware configuration interface!
Something where DC voltage comes in, and a periodic voltage comes out.
- youtu.be/eYVOdlK15Og?t=66 RC oscillator on breadboard. Produces rectangular wave. Mentions popular integrated circuit that does it: 555 timer IC.
- youtu.be/eYVOdlK15Og?t=175 LC oscillators allows for higher frequencies. Produces sinusoidal output on MHz range. Uses an amplifier to feed back into input and maintain same voltage. Hard to make reliably on breadboard.
- youtu.be/eYVOdlK15Og?t=315 crystal oscillator. Mentions it acts like an LC oscillators. Shows and equivalent model. Wish he had talked more about them. You need support components around it: similarly to the LC case, the amplifier is generally not packaged in.
Oscillator made of an LC circuit.
It resists to change in electric current. Well seen at: Video "LC circuit by Eugene Khutoryansky (2016)".
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
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.
By William Shockley in 1948 also at Bell Labs Murray Hill.
As of 2020, not used anymore in logic gates, but still used in amplifiers.
