Electronics Basics

Article Synopsis

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This article provides some basic information about electronics. It is intended for someone with very little understanding of electronic components. It provides descriptions of them, their usages, and how to work with them.
Under construction/modification by DErik (talk) 14:50, 3 January 2024 (PST)

Electronics is often a mysterious and daunting topic for many people. You know that if you stick a finger in an outlet, you will probably be serverely shocked, if not killed. So you tend to stay away from electronic innards of devices.

Well, that's probably a good thing. But the electronic devices we use in our railroads are mostly very low voltage and current. Low enough that no damage to you is ever likely to happen. In fact, it is more likely the other way around - improper handling of some of the devices will damage the device rather than you. So again, you are hesitant to mess with it for fear of damaging something in the device.

Well, that too is probably a good thing. But sometimes you have something that isn't working properly, and you need to fix it. Or it isn't working exactly the way you want it to. Or you really want or need something that just isn't available.

So, that's what this is all about. What do you need to know to fix something, or to alter something, or to create someting new? This article, and related ones will attempt to answer some of the basic questions you may have about electronics.

Concepts and Definitions

As with any subject of study, one must first know what things are. Putting labels (names) on them helps provide a frame of reference for them. So here's a few terms and names you need to know. Explanations of these items will come later. Some basic electronic concepts and definition:

Units of measure

• Ohm: The measure of resistance to current flow in a circuit or across a component of a circuit.
  The ohm (resistance) value on a schematic is usually spelled out as “ohms” or annotated with an upper case Greek omega: “Ω”. Since resistance values can be very large, the symbol may be preceded with a “k” for kilo-ohms (thousands) or “m” for mega-ohms (millions).
  In electrical formulas, the letter “R” is used to represent ohms.
• Volt: The measure of electromotive force in a circuit.
  The voltage value on a schematic is usually annotated with a “V”.
  The letter “V”, and sometimes “E” (though I consider this wrong as voltage is not the same as energy), is used in electrical formulas. Some formulas I have seen even use the letter “U”; this is definitely a very infrequent usage and I discourage it.
• Ampere: The measure of electrical current through a circuit or component.
  The current (amperage) value on a schematic is usually abbreviated as “amps” or annotated by the letter “A”.
  The letter “I” is used for current in electrical formulas (we like to keep things a little difficult, but it’s etymology can be traced back to some French historical use).
• Farad: The measure of capacitance of an electrical component to hold a voltage differential.
  The capacitance value on a schematic is usually annotated with an “F”. Since farad values are usually very small, it is frequently preceded by an “n” for nano-farads (one billionth or 0.000000001) or “m” micro-farads (one millionth or 0.000001) or a Greek lower case mu “𝛍”. Pico-farads (one thousandth of a nano or 0.000000000001) are also quite common, and that is indicated with a “p”.
  Electrical formulas involving capacitance use the letter “C” for farads. I will admit this one can get very confusing as well since capacitance formulas are based on voltage and coulombs – which is a measure of “charge” we won’t get into here, but represented by the letter “Q”.
• Coulomb: Is the charge that a capacitor with a fixed farad capacitance can attain for a specified voltage.
  This value is rarely used; I can't think of a single usage for it in our hobby. But I mention it to be complete.

How are these things measured?

• The resistance of an element is always measured without applying any external voltage to the component. The meter used to measure the resistance will provide the power.
• To measure voltage, there must be some external power supplied; the meter used to measure the voltage will not supply that power. The meter must also be connected in parallel with the circuit or component to be measured.
• The meter must be connected in series in a circuit to measure amperage.
• Measuring farad units is rarely needed. And there is no easily available device to measure a component to get that value. Hence, it is written on the component itself, or on a data sheet for the component, along with the maximum voltage that can be applied to the component, and that is all that is needed to build a circuit that includes a capacitor.

Components

• Resistor: A component expressly designed to resist the flow of electrons through it. The higher valued a resistor is, the fewer amps will pass through it. Values of resistors are encoded on the resistor with a standard color scheme.
• Capacitor: A component expressly designed to allow a voltage difference (potential) between its two poles to be built up by an external source, to hold that charge when not connected to anything, and to release the accumulated charge when conditions in the circuit change. You might not think it, but a battery might be considered to be a capacitor in some contexts; especially a rechargable battery. Capacitors may be polarized or not, and may be fixed value or variable. See the Linquip web site article that describes various types and uses of capacitors.
• Inductor: A component that generates a magnetic field around itself when a current is passed through it. Often used as a trigger switch.
• Transformer: A device that converts the voltage of one AC circuit to another voltage in another circuit. The two circuits are not physically connected. They are connected by an electromagnetic field generated by one circuit and used to induce a current in the other circuit.

Formulas

First of all, why do you need to know any of these formulas? The answer is that in order to build a circuit, or repair an existing one, you need to know what value rating a component should be to properly work in the circuit. If you can find a circuit diagram for what you want to build or repair, then you should be able to get the values from the diagram. But if you don't have the diagram, or are building a new circuit, you will have to do some calculations. Of course, you will also have to do some measuring, with a mulitmeter, to get some of the values for components in an existing circuit. In other cases, like for a new circuit, you will need the data or specification sheets that are related to the components you will need, or be able to read the values printed on the components.

• Resistance (R), voltage (V), and current (I) are pretty easy and all related to each other. The following three formulas should demonstrate that relationship:
  voltage is current times resistance: ${\displaystyle{\displaystyle V=I*R}}$
  resistance is current divided by voltage: ${\displaystyle{\displaystyle R={I\over V}}}$
  current is resitance divided by voltage: ${\displaystyle{\displaystyle I={R\over V}}}$
  When working on a circuit, all you need to know is two of these values to calculate the third.
• Farads can be calculated from coulombs and voltage, but this is rarely needed. Rather coulombs (the measure of charge on a capacitor) are calculated based on farads and voltage. And the farad value of a capacitor should be printed on the capacitor, along with the maximum voltage that the capacitor can handle. It will be the farad value that is needed when calculating things like time delay for a circuit. The ElectronicsTutorials web site has a good article on capacitors and the calculations of capacitance (farads) and charge (coulombs).

Authors and Contributors

• Author and editor: Don Erikstrup (DErik (talk) January 2024)
• Others: Please comment on this using the “discussion” tab above or send an email to MRT SIG . And contribute additional information here and in other articles.