Merge pull request #657 from WildernessLabs/develop

Get all the new hott stuff in

docs/Hardware/Reference/Algorithms/index.md

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 ---
 layout: Hardware
 title: Algorithms
----
+---
+
+* [Proportional, Integral, Derivative (PID)](Proportional_Integral_Derivative/Intro/)

docs/Hardware/Reference/Components/Common/Capacitors/index.md

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+---
+layout: Hardware
+title: Capacitors
+---
+
+
+Coming soon!

docs/Hardware/Reference/Components/Common/Diodes/Photodiodes/index.md

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+---
+layout: Hardware
+title: Photodiodes
+---
+
+Photodiodes are the opposite of LEDs, when photons enter, they get converted into electrical energy. Fun fact about LEDs; although not as efficient, they can also be used as photodiodes!
+
+![Image of a photodiode next to a United States quarter coin for scale. About 20 diodes would fit on top of the coin.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Photodiode_Medium.jpg)
+
+## Vs. Photoresistors
+
+Photodiodes differ from photoresistors in that while a photoresistor can tell you how much ambient light is present, a photodiode is really only effective at differentiating between light and dark. Unlike a photoresistor, which has a variable resistance depending on the amount of light hitting it, when light hits a photodiode, it actually converts the photons to free electrons and creates a small electric current. 
+
+In this way, photodiodes are the digital counterpart to analog photoresistors.
+
+Additionally, photodiodes are very fast, reacting to light much more quickly than photoresistors. They're sometimes used in a special opto-isolator circuits in which an LED is pointed at a photodiode to transmit digital information between circuits without having an electrical connection. In fact, fiber optic communications are done this way; an LED is connected to a photodiode via a fiber optic cable.

docs/Hardware/Reference/Components/Common/Diodes/Power_Diodes/index.md

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+---
+layout: Hardware
+title: Power Diodes
+---
+
+Power (aka _rectifier_) diodes are similar to signal diodes but are designed to handle higher current, usually `1A` or more. The [1N4001](https://octopart.com/search?q=1N4001) is a common rectifier diode and is capable of handling `1A`, but the `V`<sub>`f`</sub> (forward voltage) drop is `1.1V`. These are commonly used to protect certain parts of circuits from voltage spikes, as well as for conversion of AC to DC electricity.

docs/Hardware/Reference/Components/Common/Diodes/Schottky_Diodes/index.md

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+---
+layout: Hardware
+title: Schottky Diodes
+---
+
+_Schottky diodes_ use a piece of metal against the N-type side instead of a P-type semiconductor. This results in a much lower voltage drop and fast switching speeds and are oftenused in a clever way to get to a digital `0`/`OFF`. Used for basic logic control.
+
+The circuit symbol for a Schottky diode looks similar to the diode symbol, except that the perpendicular line looks similar to an `S`.
+
+![Illustration of the Schottky diode symbol.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Schottky_Diode.svg)
+
+Schottky diodes typically have a very low voltage drop (`V`<sub>`f`</sub>), typically around `0.2V` (`0.15V` to `0.45V`) which makes them very fast and also makes them ideal for use in simple circuit logic.

docs/Hardware/Reference/Components/Common/Diodes/Small-Signal_Diodes/index.md

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+---
+layout: Hardware
+title: Small-Signal Diodes
+---
+
+Also known as _switching_ diodes, they have an extremely fast `Trr`, and are used for fast current switching.
+
+They are one of the most common diodes available, largely because of their usefulness in high frequency circuits like radios, where their fast switching abilities are required.
+
+![](/Hardware/Tutorials/Electronics/Part6/Support_Files/Signal_Diodes_Medium.jpg)
+
+They typically have small power ratings, `150mA` or less, and a `V`<sub>`f`</sub> of `0.7V`.

docs/Hardware/Reference/Components/Common/Diodes/Zener_Diodes/index.md

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+---
+layout: Hardware
+title: Zener Diodes
+---
+
+Zener diodes have a known, precise breakdown voltage, which makes them very useful for providing a _reference voltage_.
+
+## Reverse Voltage Ratings
+
+Because Zener diodes are often used as voltage references, they come in a wide variety of reverse voltages. In fact, Zeners cover all common voltages you're likely to find in modern circuits.

docs/Hardware/Reference/Components/Common/Diodes/index.md

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+---
+layout: Hardware
+title: Diodes
+---
+
+## Intro
+
+The symbol for a diode is a triangle pointing in the direction of current (hole-flow) connected to a perpendicular line which represents the junction:
+
+![Diode symbol with a triangle pointing in the direction of current flow butting up against a line.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Diode.svg)
+
+There are a number of different types of diodes, but all of their circuit symbols are based on the one above.
+
+The [Wikipedia diode entry](https://en.wikipedia.org/wiki/Diode) lists almost 20 different types of diodes, but in practice, most circuit design only uses a handful of them. As we explore more circuits, we'll also introduce additional, specialized diodes.
+
+### Polarity
+
+To differentiate which end of a diode is the anode and which is the cathode, they usually have a marking on the end denoting the **cathode**. The following photo shows four different diodes, each with their cathode mark on the right:
+
+![Photo of four diodes showing a colored band on each diode indicating the cathode side.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Diodes_Cropped.jpg)
+
+Recall that positive charge carriers (holes) flow preferentially from anode to cathode, so the diodes above are in the same orientation as the circuit symbol below:
+
+![Illustration of a diode with the anode indicated by a plus sign and the cathode indicated by a minus sign.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Diode_Polarity.svg)
+
+### Diode Characteristics
+
+Depending on how they're constructed, a diode can have some interesting behaviors. For general diodes, there are a number of characteristics that are used to describe how they work:
+
+ * **Forward Voltage (`V`<sub>`f`</sub>)** - This is the amount of voltage drop, or the amount of voltage needed to enable current flow.
+ * **Maximum Forward Current (`I`<sub>`f(max)`</sub>)** - This is the maximum amount of current that the diode can safely conduct when forward-biased without breaking.
+ * **Peak Inverse Voltage (PIV) or _maximum reverse voltage_ (`V`<sub>`R(max)`</sub>)** - This is the maximum amount of voltage that can be applied in reverse bias without an avalanche breakdown.
+ * **Total Power Dissipation (`P`<sub>`D(max)`</sub>)** - A diode has some resistance, so some power is lost in the form of heat. As such, a diode usually has a maximum amount of power that it can safely conduct without overheating. Total power dissipation is based on the voltage of the junction potential and the current: `P`<sub>`D`</sub> = `V`<sub>`f`</sub> * `I`.
+ * **Reverse Recovery Time (`Trr`)** - This is how quickly a diode can go from `OFF` to `ON`. It's generally only important in fast-switching circuits.
+
+## Common Diodes
+
+ * **[Light-Emitting Diodes (LEDs)](Light-Emitting_Diodes)** - LEDs are a type of diode that emit photons (light) as electrons flow through the P-N junction and are used for displays, lights, etc.
+ * **[Photodiodes](Photodiodes)** - Photodiodes are the opposite of LEDs, when photons enter, they get converted into electrical energy, enabling them to be used as switches based on light.
+ * **[Switching Diodes](Small-Signal_Diodes)** - Also known as _small signal_ diodes, they have an extremely fast `Trr`, and are used for fast current switching.
+ * **[Rectifier/Power Diodes](Power_Diodes)** - High current capacity, usually `1A` or more. Used for converting AC to DC and protection of circuits from power spikes.
+ * **[Schottky Barrier Diodes](Schottky_Diodes)** - Have a very low voltage drop, so they can be used in a clever way to get to a digital `0`/`OFF`. Also very fast. Used for basic logic control.
+ * **[Zener Diodes](Zener_Diodes)** - Have a precise breakdown voltage. Typically used in a reverse bias configuration to provide a voltage reference.
+
+## Diode Uses
+
+### Flywheel Diodes
+
+Flywheel diodes protect circuits from collapsing magnetic fields created by de-powering electric motors and other coils by feeding excess current back into the coil. Typically, a power diode is used as a flywheel diode.
+
+### Voltage Clamping
+
+Voltage clamping refers to clipping a signal to a maximum/minimum value to prevent it from going outside a particular range, or shifting an entire AC signal wave above or below `0V`.
+
+![Diagram of two graphs that illustrate how a diode restricts output voltage to a reduced range.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Voltage_Clamping.svg)
+
+### Rectifiers
+
+Alternating Current (AC) electrical signals can be converted into Direct Current (DC) through a clever arrangement of diodes known as a _rectifier_:
+
+![Diagram of four diodes arranged in square pattern to form a rectifier.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Rectification_Circuit.svg)
+
+The above circuit will transform a two-phase AC wave form into positive and ground voltages:
+
+![Illustration of how a rectifier changes a two-phase AC wave that varies between -110v to +110v into a wave that varies between 0v and +110v.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Rectification_Transform.svg)
+
+With some additional components, the DC wave output above can be transformed into a smooth, level DC signal.
+
+Rectifiers are used as the first stage in converting household mains AC current into DC current for use in electronics in nearly all AC power adapters. For example, the USB wall adapter that you use to charge your phone converts AC to DC using a rectifier. In fact, nearly every electronic device around you that plugs into the wall contains a rectifier circuit.
+
+### Reverse Current Protection
+
+Because diodes act like one-way valves, they can prevent reverse current from happening in situations where a battery is plugged in the wrong way. Schottky diodes are ideal for this because their low `V`<sub>`f`</sub> means that it doesn't cost much battery voltage to protect the circuit.
+
+#### Voltage Reference
+
+Sometimes, a circuit needs a reference signal at a precise voltage. By utilizing the breakdown voltage of a reverse-biased Zener in a circuit, its `V`<sub>`f`</sub> back-pressure can provide that voltage reference. Consider the following circuit:
+
+![Illustration of a circuit utilizing a Zener diode to provide a 5V voltage from a 9V source.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Zener_Voltage_Reference_Circuit.svg)
+
+In the circuit above, a Zener with a `5V` breakdown voltage is being reverse biased with `9V`, which means that it's breakdown threshold has been reached, and will conduct current, with a `5V` voltage drop. Since the voltage drop acts like a dam, no matter how much voltage is applied, `5V` of back pressure will always be present:
+
+![Illustration of the analogy of a Zener diode acting like a dam for water flow.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Voltage_Reference.svg)
+
+As long as the current is limited, in this case with a resistor, it will stay within that precise operating band. Recall the diode behavior chart from before, specifically the breakdown behavior:
+
+![Illustration of the diode breakdown curve.](/Hardware/Tutorials/Electronics/Part6/Support_Files/Diode_Reverse_Behavior.svg)
+
+While this circuit looks a lot like a two resistor voltage divider, it's got a huge advantage over a divider; as long as the current is limited, no matter what amount of voltage is applied (within the diode's tolerance), the `V`<sub>`out`</sub> reference will always be the same.
+
+And while the limited amount of current prevents this from being a useful voltage regulator, it does serve as a reliable voltage reference, which is used in ADC conversions, voltage regulator circuits, and more.
+
+

docs/Hardware/Reference/Components/Common/Resistors/Reading_Axial_Resistors/index.md

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+---
+layout: ElectronicsTutorial
+title: Reading Axial Resistor Values
+subtitle: Determining a resistor's value from its band markings.
+---
+
+## Axial Resistor Colored Bands
+
+Axial resistors, the kind that is most often used when prototyping, have color coded bands that specify the resistance value and tolerance of the resistor. They usually come in 4 or 5 band flavors, with 5 band resistors being more precise.
+
+To read a banded resistor, align it so that the three (or four) closely spaced bands are on the left, and the furthest spaced band is on the right. Then, use the following chart to determine the values from left to right:
+
+![Chart of translating 4-band resistor color bands into a resistor value and tolerance (with four bands for value and 1 band for tolerance), where the left three closely spaced bands translate to unit values, the fourth closely space band translates to a multiplier value, and the furthest spaced band translates to a tolerance percent.](/Common_Files/Reading_Axial_Resistors.svg)
+
+The first 2 (or 3 bands, on a 5-band resistor) specify the resistance value, and the 3rd (or 4th) specify the magnitude multiplier. 
+
+### Sample Reading
+
+For example, the resistor shown above has the following values:
+
+* Brown = `1`
+* Blue = `6`
+* Black = `0`
+* Orange = `1k` Magnitude Multiplier
+* Gold = `5%` Tolerance
+
+Therefore, the resistor has `160Ω * 1k = 160kΩ`, with a tolerance of `±5%`.

docs/Hardware/Reference/Components/Common/Resistors/index.md

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+---
+layout: Hardware
+title: Resistors
+---
+
+### Circuit Symbol
+
+In an electronic circuit schematic, a resistor is typically symbolized as the following:
+
+![Circuit symbol for a resistor; a zig zag line with leads extending from both ends.](/Common_Files/Circuit_Symbols/Resistor.svg)
+
+### Axial Resistors
+
+[Reading Axial Resistors](Reading_Axial_Resistors)

docs/Hardware/Reference/Components/Common/Transistors/High-Side_MOSFET_Circuit/index.md

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+---
+layout: Hardware
+title: High-Side MOSFET Circuit
+---
+
+## P-Channel MOSFET
+
+High-Side MOSFET circuits must be switched with a P-Channel MOSFET, which can be controlled by an N-Channel MOSFET:
+
+![](/Hardware/Tutorials/Electronics/Part7/Support_Files/High-SIde-P-Channel_w_N-Channel_Control.png)
+
+When the N-Channel gate is pulled `LOW`, it's off, and nothing flows through it. When the gate is pulled `HIGH`, then electrons are allowed to flow from `GND` to the P-Channel gate, and it turns on, in turn, energizing the load.

docs/Hardware/Reference/Components/Common/Transistors/Low-Side_MOSFET_Circuit/index.md

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+---
+layout: Hardware
+title: Low-Side MOSFET Circuit
+---
+
+## Using an N-Channel MOSFET as a Low-Side Switch
+
+Let's say we wanted to control a load such as a DC motor. A very simple and efficient design would be via a low-side, N-Channel MOSFET:
+
+![](/Hardware/Tutorials/Electronics/Part7/Support_Files/LOW-Side.png)
+
+In this case, the voltage between the `Gate` and `Source` is +3.3V. It enables the `Gate` to fill with positively charged holes, which attract the minority charge carriers from the surrounding P-Channel semiconductor, in this case, the negatively charged electrons to create an N-Channel conductor between `Drain` and `Source`:
+
+![](/Hardware/Tutorials/Electronics/Part7/Support_Files/MOSFET_Gate_Double_Voltage.svg)