As you browse this website, you will find videos on many of the pages. These videos are also all posted on YouTube and organized into playlists on the ElectronX Lab channel:
On this website I am also curating and organizing these videos to help make them easier to find. This is what I have so far:
Or you can go directly to my YouTube channel.
Title background picture: © tilialucida via canva.com
Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) are common, three lead semiconductor devices. The two primary purposes of MOSFETs are to act as voltage controlled switches (pretty much all digital integrated circuits (ICs) are created from MOSFETs) or as amplifiers. The three leads of a MOSFET are called the gate, source, and drain. The basic physical operation involves applying a voltage between the gate and source to control the conductivity of a channel between the source and the drain. The videos below provide a little bit more detail for the two broad categories of MOSFETs which are called depletion MOSFETs and enhancement MOSFETs.
Depletion MOSFETs have a conductive channel between source and drain by default. In other words, they are “normally-ON” devices. The existing channel can be depleted by a voltage applied between gate and source to turn the channel off. Watch this video to find out more:
Enhancement MOSFETs must be “enhanced” to create a conductive channel between source and drain. In other words, E-MOSFETs are “normally-OFF”. To create this channel a voltage must be applied between source and drain.
E-MOSFETs are used primarily as switches, i.e., they are devices that are either on or off. In fact, pretty much all digital circuitry is created from complementary MOSFET (CMOS) circuits which are digital circuits created using P-channel and N-channel E-MOSFETs. This video focuses more on standalone switches that control current to a load (i.e., a voltage at the gate determines whether a load is turned on or off).
The set of videos below describes three of the most important concepts of voltage amplifiers, that is the voltage gain, the input impedance, and the output impedance. (There are of course many other amplifier characteristics, such as bandwidth, common-mode rejection, power supply rejection, noise characteristics)
Voltage gain is the multiplying factor an amplifier applies to the signal that is input to it. The voltage at the input gets amplified (multiplied) by the gain to give an output with a new (generally higher) amplitude. The amplification factor or gain can be stated strictly as a number (which is the factor by which the output is bigger than the input) or as a decibel. The video below goes in to all of these details
[adrotate banner=”3″]
Input impedance is the impedance seen by a signal when it is applied to the input of an amplifier. The input impedance is important to know because, it, combined with the output impedance of the input to the amplifier result in a voltage divider across output impedance of signal source and input impedance of the amplifier. This voltage divider means the signal will be attenuated somewhat. If this is not making much sense, then the video below will help clear things up.
Output impedance is the impedance a signal sees as it is leaving an amplifier (or other signal source). If the output is connected to a load (e.g., a speaker), or to the input of another device, there will be a voltage divider between the output impedance and the load which can result in some amount of signal attenuation. The video below describes this effect in more detail.
JFETs, or Junction Field Effect Transistors, are three terminal devices that can be used as switches and amplifiers (amongst other things). They are not commonly used anymore but can still be found in some applications. Studying them, though, can give a good understanding of the effects of electrical fields in semiconductor devices.
The set of videos below provides a good introduction to the analysis of JFETs and circuits that use JFETs. These videos include:
[adrotate banner=”3″]
Biasing is the process of configuring the circuit around the JFET to set voltages and currents to specific values to put the JFET into a particular state (e.g., open the channel between the source and the drain). These two videos describe the different states that JFETs can be in and provide some example biasing circuits.
A small signal model is a model that can be used to model only the behaviour of the AC portion of a signal applied to a circuit. The small signal model ignores biasing but assumes that the biasing is putting the device into its proper state. This video describes the AC model of a single stage JFET amplifier (including transconductance). This is a rather long video, but it shows both a graphical method and a numberic method for determining characteristics of the JFET small signal model.
[adrotate banner=”3″]
The common source amplifier configuration has the input AC voltage applied at the gate and the output taken at the drain. It is analogous to the common emitter BJT amplifier. This video shows how to analyze a couple of different common source configurations (i.e., one with the source resistor bypassed, one without a bypass) to determine the amplifier gain, input impedance, and output impedance.
The common drain amplifier configuration of a JFET is analogous to the common collector (emitter follower) configuration of a BJT. It has the input applied at the gate and the output at the source. This video shows how to determine the input impedance, the output impedance and the voltage gain of three different common drain circuits (each has a different biasing configuration).
Bipolar junction transistors, or BJTs, are three terminal semiconductor devices and are a basic building block for many integrated circuits (although they have mostly been replaced by FETs). They can also be used individually (as discrete devices) and are commonly used as switches or amplifiers. This set of videos below goes through the basic features and characteristics of BJTs and describes how to analyze and design simple BJT circuits. The specific video topics are:
A BJT characteristic curve shows the relationship between the current through the collector and the voltage across the Collector-Emitter. Typically, there are several different curves for different values of base current. To obtain a characteristic curve, apply a particular base current, then sweep VCE through a range of values from 0 up to a maximum while measuring IC at several points. The characteristic curve can tell you a lot about the behaviour of the BJT. Watch the video below to find out more.
[adrotate banner=”3″]
A base biased circuit is one where the base voltage (and therefore base current) is set by its own individual voltage source. This is an inefficient configuration, but can help with the understanding of what BJT biasing is.
A fixed bias or fixed point bias circuit has the base connected through a resistor to the same voltage source as the collector/emitter side of the circuit. This configuration reduces the number of required voltage sources to one, but the operating point is very dependent on the beta value of the transistor.
A voltage divider biased circuit sets the base voltage by using a voltage divider at the base. With proper selection of the resistors in the voltage divider circuit, the analysis of these kinds of circuits can be greatly simplified. The operating point of voltage divider bias circuits are not very sensitive to the value of beta for the transistor (this is a good thing).
A BJT can act as a switch and it works by controlling the current to the base. The switch operation is an example of a small amount of current controlling a large amount of current. In this case, a small base current, turns the switch on and allows a large amount of current to flow from the collector to the emitter.
Up to this point, we’ve only considered BJTs in DC circuits, but all of the biasing we’ve discussed is not very useful (except in the case of switches) unless there is an AC signal as well (typically an AC input that gets amplified by the circuit). The first step to understanding BJT amplifiers is to gain an understanding of the operation of BJT circuits when AC signals are applied.
[adrotate banner=”3″]
Arduino, Light Sensor, and HTTP Requests
It is actually fairly simple to start building your own little corner of the Internet of Things. These videos help you get started with doing just that by helping you build a system using a couple of sensors, an Arduino, an Internet connection and a cloud based service called ThingSpeak.
[adrotate banner=”3″]
The program cURL is a handy command line based tool for generating application layer networking messages in various protocols. The reason I am including it here in my Internet of Things videos is because you can generate HTTP and HTTPS messages with it. Many cloud based IoT services support a REST API which is an interface to the service via HTTP requests. For example by sending an HTTP POST request you can send data to the cloud service for it to store in a database and by using an HTTP GET request you can obtain that data back from the cloud. cURL would typically not be used in the final product, but it is a very handy debugging tool to test the interface
ThingSpeak is an Internet of Things software as a service platform. It allows you to create a channel which can accept a stream of data (from a sensor network for example), store it, and display it through a website. It also allows you to obtain the data. The interface to send or retrieve data can be through a REST API (using HTTP) or the MQTT protocol. ThingSpeak is owned by The Mathworks and so can interface nicely with Matlab. The video below shows how to setup an account and then interface toThingSpeak using HTTP via cURL.
ThingSpeak uses a REST API as the interface to its database and this video shows how to use the API (via HTTP GET requests) to obtain data from a ThingSpeak channel.
An internet connected Arduino can be used to send data to ThingSpeak. All you need to do is collect your data (in this thing I am measuring Lux using an LDR) and then creating an HTTP POST request that you send to the ThingSpeak server.
Diodes are the simplest of electronic devices. At their most basic, they are like one-way valves for electrical current, but they can be used for so many different things. Common applications include voltage rectification, voltage regulation, circuit protection, current control, and even simple (but inefficient) logic circuits. On this page you will find videos on
[adrotate banner=”3″]
The way that electrons flow in doped semiconductors is very interesting, but the really interesting effects occur when you have p-type semiconductor and an n-type semiconductor created side by side to create a PN junction. The properties of the PN junction make it useful for several important electronic devices. The most basic such device is the diode which is simply a PN junction with leads on it to allow it to be used in a circuit.
When you have a diode in a circuit, you will often want to predict its behaviour, or conversely, you want a certain behaviour in ac circuit and want to ensure the diode will exhibit that behaviour. Diode modelling is the process of creating a mathematical or behavioural model of the diode that helps you to predict how the circuit will behave (electrically speaking) with the diode in it. Depending on the level of precision you want in your model, there are different models that you can choose from. This video describes several different models that you can use for diodes
In case just knowing the theory behind modeling diodes is not enough, this video looks at a few simple examples and analyzes circuits using different diode models. The forward bias models used are:
[adrotate banner=”3″]
Half wave rectifiers can be created using a single diode in an AC circuit. Since diodes only allow current to pass in one direction, they will only allow current to flow during half of an AC circuit. Half wave rectifiers cut off half of the signal and this video shows how they work:
Full-wave rectifiers force AC current to flow through a circuit in one direction by using a clever configuration of diodes. Full-wave bridge rectifiers fulfill a very important stage in AC-DC conversion.
