Circuits can be things of stupefying power and complexity, responsible for everything from changing channels on t.v. to controlling spacecraft as they exit the outer boundaries of the solar system.
But for all that, there are a handful of basic components found in very nearly every circuit on the planet. An understanding of these components can go a long way toward making electronics more comprehensible.
Resistors have the charming quality of doing exactly what their name implies, i.e. they resist the flow of electrons in a circuit. This is useful for keeping LEDs within acceptable ranges so they light up but don’t blow out, for creating voltage dividers for use in resistive components like photocells or flex sensors, and for incorporating things like buttons into circuits through the use of pull-up resistors.
- Sparkfun’s resistor tutorial is carefully done and is the source of the examples of resistors cited in the above paragraph.
- Resistorguide’s thorough exploration of resistors is notable for its discussion of different kinds of resistors and the pros and cons of using each.
- This ScienceOnline tutorial carefully walks through how to interpret the colored bands found on most resistors, and demonstrates the effect on an LED’s brightness of running the same current through different resistors. It also notes that graphite is similar to the material used to make resistors, and does two fascinating little experiments with pencil marks on paper acting as a resistor in a circuit.
- GreatScott’s resistor video repeats much of the information in the other videos but succinctly explains what pull-up and pull-down resistors are.
Capacitors come in a wide variety of styles — ceramic disk, polyfilm, electrolytic — but all are designed to exploit properties of electromagnetic fields to store electrical charge. They are built by separating two conductive plates either with space or with a nonconducting material called a dielectric. When current is applied to a circuit with a capacitor, negative charge piles up on one plate. The dielectric won’t conduct electricity but it can support an electric field, which gets stronger as electrons accrue on one side of the capacitor. This causes positive charges to gather on the other plate, and the electric field between the positively- and negatively-charged plates stores a proportional amount of power, which can later be discharged.
- Collin Cunningham elucidates capacitors by ripping one apart, delving briefly into their history, and then constructing one from a pill bottle and some aluminum foil.
- HumanHardDrive approaches capacitors and capacitance from a theoretical standpoint, delving into the chemistry and math involved.
- Eugene Khutoryansky offers an even more granular look at what’s going on inside capacitors.
Like capacitors, inductors store electrical energy. A typical inductor will be made up of metal wire wrapped around something like an iron bar. When current is applied to an inductor a magnetic field begins to build and when current is cut off it begins to disintegrate. As a rule magnetic fields don’t like changing, so the generated field resists the initial increase in current and the later decrease in current. Once current levels off, however, the inductor will act like a normal wire for as long as the current doesn’t change.
As I wrote about in “The STEMpunk Project: Literally Reducing a (Black) Box“, inductor motors exploit these electromagnetic properties to generate torque for applications like spinning fan blades.
- Eugene Khutoryansky does another fantastic job in his video on the behavior of inductors in a circuit.
- Afrotechmods spends a lot of time demonstrating how current changes in response to different inductance values.
Diodes are small semiconductors whose purpose in life is to allow current to flow in one direction only. If a negative voltage is applied to a diode it is reverse-biased (“off”) and no current can flow, but if zero or positive voltage is applied it is forward-biased (“on”) and current can flow from its anode terminal to its cathode terminal. If enough negative voltage is applied to the diode, it is possible for current to begin flowing backwards, from the cathode terminal to the anode terminal.