Electronics

Independent sources produce constant voltage. Batteries are an independent source, op amps are a dependent source.

When we suppress something, we treat it as if it has no voltage drop. That is, we ignore resistance, and all resistance has voltage drops.

The word for resistance in an AC circuit is an impedance matcher (such as the horns in a microwave). In a DC circuit, capacitors have no resistance. The impedance of a capacitor changes depending on the frequency run in the circuit. A bridge rectifier (using 4 diodes forming a diamond-shape) takes AC voltage to DC voltage.

Semiconductors are useful to build diodes. Diodes: sandwich an n-type and p-type together, which acts as a 1-way gate. Diodes only let current flow through in 1 direction. Diodes do not change the voltage drop much.

A transistor is purely an electronic switch, and not mechanical. 2 types of transistors: bipolar, and field effect, both with 3-prongs (or pins), which are the emitter, base, and collector. The 2 types of bipolar transistors: n|p|n and p|n|p. Their 2 main functions is to switch circuits on or off, and amplify signals. Transistors are used to build logic gates. They can control the flow of electrons from the source to the drain using a gate and a voltage. An analogy is a drinking fountain, where water goes from its source to a drain, and that flow is controlled by a gate, which can be opened or closed by using some energy.

Transistors are active devices while resistors and capacitors are passive devices (they cannot actively control or amplify a signal, only change them as it passes through them).

LEDs (light-emitting diodes).

LEDs are a semiconductor device that emits light when current flows through it, where electrons recombine with electron holes, releasing photons for energy. The color of the light, which corresponds to the energy of the photons, is determined by the energy required for electrons to cross the band gap of the semiconductor. LEDs converts some of the energy of electron-hole recombination into light. This radiative recombination process always occurs in competition with non-radiative recombination, in which the energy is simply converted to heat. When light is emitted from an LED, the photon energy is equal to the bandgap energy. Because of this, LED lights have pure colors and narrow emission spectra relative to other light sources.

The 1st LED was IR, then red, made by Nick Holonyak both in 1962 at General Electric. The 1st yellow-green LED came 1972, by M. George Craford, at Monsanto, and the 1st blue LED came in 1992 and 1993, the 1st by 2 Japanese researchers at Nagoya University (Dr. Isamu Akasaki and Hiroshi Amano), and the 2nd by a Japnese engineer at Nichia Corporation (Shuji Nakamura), where they all won a Nobel prize for it in 2014. The 1 in 1993 was considerably brighter than the 1 in 1992. The 1st 1 was using gallium nitride crystals (on top of aluminum nitride that was on top of sapphire, and later just with magnesium), the 2nd using indium gallium nitride material (directly on top of sapphire). The 2nd 1 later developed into purple LEDs around the same time. The red LED was from gallium arsenide phosphide (GaAsP) material, the green LED from gallium phosphide (GaP). Note that also in 1972, an RCA engineer named Herbert Maruska invented a blue LED made of gallium nitride, but it was incredibly dim and inefficient.

Red LEDs require 1.9 eV, green 2.4 eV, and blue 2.7 eV (the latter requires more energy, and therefore require a larger band gap). You can think of band gaps as an aisle between 2 columns of seats in a movie theater, where humans (the electrons) occupy 1 column of seats on 1 side of the aisle, while the other aisle remain empty seats. In order for Nakamura to invent the blue LED, he got permission from the CEO of his company, to move to Gainesville, Florida, and work with a colleague whose lab was beginning to use a new crystal-making technology. Therefore, Nakamura learned how to build and fix metal-organic chemical vapor deposition reactors. White LEDs were made in 1996 by placing a yellow phosphor over the blue LEDs, which absorbs the blue photons and re-radiates them in a broad spectrum.

Pulse-width modulation is to make a LED dimmer, by making it blink more.

LEDs use about 75% less energy and last 25 times longer than incandescent bulbs.

Quantum dots are semiconductor particles that absorb UV and emit light.

Band gaps.

In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is the energy required to promote a valence electron bound to an atom to become a conduction electron, which is free to move within the crystal lattice and serve as a charge carrier to conduct electric current. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move in the solid; however, if some electrons transfer from the valence to the conduction band, then current can flow. Substances with large band gaps are generally insulators, those with smaller band gaps are semiconductors, while conductors either have very small band gaps or none, because the valence and conduction bands overlap.

The delocalized pi orbital is the highest occupied molecular orbital (HOMO), and the pi* orbital is the lowest unoccupied molecular orbital (LUMO). In organic semiconductors, the HOMO takes the role of the valence band while the LUMO serves as the conduction band. The energy separation between the HOMO and LUMO energy levels is considered the band gap of organic electronic materials and is typically in the range of 1-4 eV.

Piezoelectric crystal.

A piezoelectric crystal is a crystal that generates an electric field. Their ability to transform electrical oscillations into mechanical vibration, and vice versa, is the basis of their use.

When quartz is mechanically deformed, an electric potential develops across its surface, then the crystal deforms. A crystal connected in a electrical circuit oscillates at a frequency that is proportional to the mass and shape of the crystal which is amazingly constant. (This property is the piezoelectric effect.).

Squeezing a quartz crystal gets a voltage, running a current through it makes them oscillate.

The human eye, for example, acts as a transducer, converting radiant energy into electrical signals that travel along neurons. (A transducer is a device that converts a physical or mechanical variable to an equivalent voltage or current.).

Transformers.

Transformers can be blown up if you connect 2 in series. A transformer in a microwave (step-up transformer) takes 120 V from the wall, and turns it to about 2000 (or 1920) V, (from 170-V peak to 2715-V peak). This is extremely dangerous. A transformer in a phone charger (step-down transformer) takes 117 volts from a wall, and turns it into about 3-5 V, to charge the phones batteries.

Transformers in microwaves and cell phone chargers only do one thing. They convert AC voltage to a different AC voltage. A switch-mode power supply is a DC-DC converter (increasing/decreasing 1 DC voltage to another). In cases where you needs to convert AC to DC, you use a rectifier. This is usually a full bridge rectifier. If you're using a transformer, you scale the voltage, then rectify (convert AC to DC). If you use a switch-mode power supply, you rectify, then scale the voltage. Modern cell phone chargers use switch-mode power supply.

The opposite of a rectifier, or something that converts DC to AC, is an inverter. In alleys, the gray garbage-can shape are called (pole-mounted) distribution transformers.

Note: when given the load, if voltage is increased by a transformer, the current is increased as well. But you cannot increase the voltage by increasing the current, current is only increased when voltage is increased or when resistance is decreased. Current is the measure of flow rate.

Multimeters.

To measure the voltage of a capacitor using a multimeter, switch the voltage to DC, and connect the red wire to positive end, black wire to negative end. To measure a diode, connect the black wire to the end of the diode with the stripe, and red wire to other end, to give a reading in volts. That is the minimum voltage needed to open the diode to allow some current to flow. To measure a wall outlet, put the black into the neutral (left) or ground (bottom) outlet, and red into the hot side (right). You do not want to start the red 1st, or take out the black with the red still attached, so red comes out 1st.

Note that the capacitance of a capacitor in a microwave and transformer is not to be measured with a multimeter, or with an oscilloscope (that measures up to 150 V), as it reaches 2000 V.

When the multimeter says 0L, it stands for outside the limit.

Multimeters can be used to check if an extension cord works or not. Change the reading to resistance, put the black alligator clip on 1 side, and the red needle inside the other end. You can do a wiggle test, where you bend the wire near where you put the red needle to see if has an intermittent failure.

Prior to buying a multimeter, 1 can already have a non-contact voltage tester, and outlet tester, which are simpler.

Casette tapes.

An analog signal is a continuous stream, which in the case of audio has instantaneous amplitude proportional to air pressure variation. The pattern of magnetism put on a compact cassette has superimposed cycles of an ultrasonic frequency. This is an inaudible "bias" signal that overcomes distortion caused by the magnetic hysteresis of the ferric oxide tape coating.

Touchscreens.

Touching the screen with or without gloves detects a measureable change in capacitance (between the wires), as gloves block an electrostatic field. The touchscreen detects the change, and touchscreens are designed to detect the capacitance when touched. Touchscreens are composed of 2 transparent diamond-grid patterns printed on polyester with an optically clear insulator in between. The diamond-grid pattern is printed with a transparent material of indium tin oxide, which acts as a conductor. Below the touchscreen is the display, which uses LCD (liquid crystal display) or OLED (organic LED). For OLED, smartphones in 2018 can have over 3.3 million pixels. Each pixel is composed of a red, green, and blue light. Each subpixel is controlled by a thin film transistor that acts as a dimmer switch.

3 types of antennas:

-The modern dish-TV antennas. Consisting of a dish (parabolic shaped reflector) and a LNBF (low-noise block down converter). The LNBF is made of a feedhorn, a waveguide, 2 perpendicular probe, and a PCB. The voltage is induced in the probe, and goes to the PCB for signal processing (such as filtration, amplification, and conversion from high to low frequency. Regarding the 2 probes in a LNBF, 1 is for horizontal and 1 is for vertical polarized signals.

-The older dipole antennas (called Yagi-Uda antenna). The dipole converts the received signals into electrical signals.

-The antenna found in smartphones, called patch antenna or (planar inverted F antenna). It consists of a metallic strip placed on a ground plane with a piece of dielectric material in between. The metallic patch acts as a radiating element

Antennas can be made if we can arrange an oscillation of positive and negative charges. The size of the antenna should be half of the wavelength.

Garage door and garage door openers:

Fun fact: Did you know that in the 1950s to 1970s, there was no feature to halt a garage door that was half-way down. It either went up all the way, or down all the way, with no pause ability. But today, if you use a garage remote control made from a different company, it still does not have this halt feature. In the U.S. for example, LiftMaster and Chamberlain are part of the same parent company, and garage remotes made from either company has these 3 features. However, if a garage remote is made from a different company, multi-compatible company, such as Genie, it does not have the ability to halt a garage door mid-way.

Refrigerators.

The 4 components of a refrigerator where a refrigerant enters, are a compressor, condenser, expansion valve, and evaporator. Refrigerant enters compressor as a low pressure warm gas, leaves as a high pressure hot gas (volume decreases), converted to warm liquid in condenser (still high pressure), then in expansion valve, refrigerant expands, so temperature and pressure drops, becomes low pressure cold liquid, then evaporator turns it to a gas, then is sucked back to compressor.

The traditional refrigerator with the freezer over the fridge, are called topmount, whereas the parallel door fridges are called side-by-side. The thing that looks like a black pot is the compressor, whereas the thing that looks like a radiator, is the condenser.

Appliance companies do buy other appliance companies. Haier wanted to buy Maytag for $1.28 billion, and the bid failed, in which Whirlpool bought Maytag for $1.7 billion in April 2006, but Maytag still gets to keep their brand name. Haier however, a Chinese multinational company, bought GE Appliances in 2016 for $5.4 billion.

Fixing refrigerators.

Refrigerators are proprietary, so each company can make their own parts. A company technician can come over to replace parts, and they would only fix appliances that their company makes. In 2024, having a refrigerator technician come over can charge $125. If they find out the cause is a broken relay, and replace the relay, can cost $370. If they replace the old relay with a new 1, and the refrigerator still doesn't work, they'll most likely say you have to buy a new 1. If they were to replace the compressor, would charge around $1500, in which they would say you're better off buying a new 1. Condensers are unlikely to be replaced, as the only time they would need to be replaced is if they are leaking refrigerants.

What is the relay? It helps control the compressor, and starts it up. It provides a brief burst of additional electrical current to the compressor's start winding. The relay can also prevent the compressor from drawing too much current. The relay does not turn off the compressor though, that is done by the thermostat in older refrigerators, or by the control board in newer refrigerators.

Refrigerators and HVAC systems are closed-loop systems, meaning the refrigerant circulates continuously between the evaporator and condenser without being consumed. So, you should never need to refill refrigerant unless there's a leak. Most modern systems use R-134a, R-410A, or R-600a, depending on the appliance. R-22 is now banned for new use in the U.S. in 2020 due to environmental concerns.

University plant refrigerators: storing and preserving plant samples at -80 C is costly for the universities and the environment, for transcriptomics. Each -80 C freezer consumes about 20 kWh/day, which is as much energy as the average U.S. home, according to the U.S. Federal Energy Management Program.

Fixing gas stoves.

If your stove's spark is not igniting, you may be better off buying a new 1. If the ignites, but no flame comes out, you can test it to see if debris is preventing the flames from igniting. During the igniting process (the click click click noise), you can use a lighter and put it next to the burner, to see if the flame finally comes. If you don't have a lighter, but 1 of the stove's 4 burner works, you can use a paper towel to lit it on fire from a working burner, then use it next to a burner during ignition.

If that works, then this becomes a cleaning issue. Remove the burner and burner's cap to wash them both. Wash them 1st in baking powder with hot water, then with vinegar with hot water, with some scrubbing during soaking. It's not recommended to use hydrochloric acid since the burners are made of aluminum. The golden spark is made of brass. The cast iron does not have to be cleaned.

Solar panels in the U.S.

The concept of solar panels involves 3 companies, but having them installed on your roof only involves 1. The company that installs the solar panels on your roof, does not manufacture them, and the company that makes solar panels, don't install them. The company that makes solar panels also do not make the inverters for them. So there are solar panel companies, companies that make inverters for solar panels, and companies that install and configure them together.

For inverter companies in the U.S., 2 companies dominate some 85% of the market: SolarEdge and Enphase. SolarEdge make string inverters, which converts DC to AC. Enphase makes microinverters, which is "per panel" instead of stringing all the panels together. For string inverters, if something goes wrong with 1 panel, the whole system stops working. SolarEdge sells direct current (DC) optimized inverter systems for solar photovoltaic (PV) installations.

Who pairs which solar panel company with which inverter company? The installation company chooses them. In 2021, the whole system can cost about $17,000, to be made in 3 payments.

How efficient are solar panels? According to Axitec, a German company that makes solar panels, says their solar panels range in efficiency from 15.37% to 20.45%, as of 2024, and have an output warranty lasting for 25 years.

Sunrun takes a different approach, as a solar utility. It leases panels and batteries to homeowners, collecting monthly payments while handling all the upkeep. It’s a lot more sensitive to interest rates and policy shifts than Enphase and SolarEdge.

Tesla acquired SolarCity in 2016 for approximately $2.6 billion in stock. SolarCity was co-founded by Lyndon and Peter Rive, cousins of Elon Musk. Vivint Solar was acquired by Sunrun in a deal announced on July 6, 2020, and completed on October 8, 2020, for about $3.2 billion in an all-stock transaction. The merger created the largest residential solar company in the U.S., surpassing Tesla in terms of total installations (Tesla Energy is a division of Tesla, Inc.).

History.

What years did flat-screen TVs surpass cathode-ray TVs in the U.S., and when did LED light bulbs surpass incandescent light bulbs in the U.S.?

1. In terms of sales, 2007 was a significant turning point when flat-screen TVs, including LCD and plasma models, became more affordable and widely available. Flat-screen TVs began to consistently outpace CRT TVs.

By 2010, flat-screen TVs had become the standard, and CRT TVs were almost entirely absent from store shelves in the U.S.

LCD (Liquid Crystal Display) uses liquid crystals sandwiched between layers of glass.

Plasma TVs use tiny cells filled with a gas (typically neon and xenon) that is electrically charged to produce ultraviolet light, which excites phosphors to emit visible light.

Plasma TVs here heavier and more expensive than LCDs, as well as consumed more power.

Plasma TVs were popular in early 2000s, and were phased out by mid-2000s. However, no company that made plasma TVs, exclusively made plasma TVs. Panasonic was known for being 1 of the biggest advocates of plasma TVs, but also made others TVs. Same with Samsung, LG, Pioneer, and Hitachi.

2. In terms of sales and usage, during the late 2010s. A starting point is the Energy Independence and Security Act (EISA) of 2007, where legislation required higher energy efficiency standards for light bulbs, effectively phasing out most traditional incandescent bulbs starting in 2012, where manufacturers shifted focus to more on compact fluorescent lamps (CFLs) and LEDs.

Around 2015, LED prices dropped significantly, becoming cost-competitive with CFLs while offering superior performance and lifespan.