10/20/2020 at 16:21 •
As noted in our previous column, in the not-so-distant future we’re going to start creating simple circuits using resistors and light-emitting diodes (LEDs), but we first need to learn enough about resistors to ensure we use the right ones when the occasion demands.
Unfortunately, it isn’t realistic for a manufacturer to create a collection of resistors comprising every conceivable value in a cost-effective manner. Furthermore, the people who use resistors couldn’t afford to purchase all of the different values and wouldn’t have the space required to store them if they did.
The solution arrived at by the industry was to adopt a selection of standard values, which has the added advantage of allowing users to second-source their resistors from multiple manufacturers. The real trick was for everyone to agree on the values forming the standard set.
As we discussed in Part 10, in 1877, a French military engineer called Charles Renard proposed a scheme of preferred numbers that allowed the French army to reduce the 425 different sizes of ropes they required to keep their balloons in the air to only 17 sizes that covered the same range.
In Renard's system, the interval from 1 to 10 was divided into 5, 10, 20, or 40 steps, which we now refer to as the R5, R10, R20 and R40 scales.
The E Series of Preferred Numbers
In 1952, the IEC (International Electrotechnical Commission) defined a set of standard values for different types of components, including resistors. Collectively referred to as the “E series,” this actually consists of the E3, E6, E12, E24, E48, E96 and E192 series, where the number after the 'E' designates the quantity of value "steps" in each series.
Let’s start by looking at the E12 series. One way to represent this mathematically is as follows (where the symbol ≈ means “approximately equal to”):
10(0/12) = 1
10(1/12) ≈ 1.2
10(2/12) ≈ 1.5
10(3/12) ≈ 1.8
10(4/12) ≈ 2.2
10(5/12) ≈ 2.7
10(6/12) ≈ 3.3
10(7/12) ≈ 3.9
10(8/12) ≈ 4.7
10(9/12) ≈ 5.6
10(10/12) ≈ 6.8
10(11/12) ≈ 8.2
10(12/12) = 10
Another way we can look at this is graphically as shown below. Since this scheme is based on a logarithmic approach, and since the E12 series employs 12 subdivisions, observe that each new number can be generated by multiplying the previous value by 10(1/12) ≈1.21.A graphical representation of the E12 scale (Image source: Max Maxfield)
Remember that these values repeat for every decade, which means we can summarize them in a table as shown below.A tabular representation of E12 resistor values (Image source: Max Maxfield)
Through-Hole vs Surface-Mount
Warning -- incoming abbreviation storm! There are two main ways to attach electronic components to printed circuit boards (PCBs). The first is through-hole technology (THT), which is also known as lead through-hole (LTH). The second is surface-mount technology (SMT), whose components may be referred to as surface-mount devices (SMDs).
In the case of THT, component leads are run through copper-plated holes that pass through the PCB. Solder is then applied to attach the component leads to copper pads associated with the holes. By comparison, in the case of SMT, the SMDs are soldered onto pads on the surface of the board. For the purposes of these columns, we will be working with THT components whose leads we will plug into holes in breadboards (don’t worry; all will become clear when the time is ripe).
Resistor Color Codes
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09/24/2020 at 18:08 •
In the not-so-distant future, we’re going to start creating simple circuits using resistors and light-emitting diodes (“Ooh, Shiny!”). However, in order to warm ourselves up for this awesome experience, we first need to learn a little more about resistors to ensure that we use the right ones when the occasion arises.
Before we start, I’m going to make the assumption that you’ve read the previous columns in this series, which means you should have at least a vague idea as to what a resistor is and what it does. If not, this would be a really good time to do so (LOL).
Also, before we start, a small word of warning. Do you remember being introduced to the concept of logarithms at school? Did you enjoy meeting them as much as I did (which is to say, not a lot)? Well, I’m afraid we are going to lightly touch on them here, but you don’t need to worry because it’s not going to hurt (me) at all.
As an aside, if you aren’t comfortable with logarithms, which were introduced by the Scottish mathematician, physicist, and astronomer John Napier in 1614 as a means of simplifying calculations, then this would be a great topic for you to read up on in your own time, because they have all sorts of cool attributes and uses (you might also want to check this Intro to Logarithms Video from the Khan Academy).
Different Types of Resistors
Resistors can be created from a wide variety of materials using a multiplicity of techniques. If you hang out with dubious people in strange places, you may hear talk of Carbon Composition, Carbon Film, Ceramic, Metal Element, Metal Film, Metal Foil, Metal Oxide Film, Thick Film, Thin Film, and Wirewound resistors (and I wouldn’t be surprised to discover that I’ve left some out).
Each type of resistor has its own advantages and disadvantages. For example, one type of resistor may cost more than another, but its resistance may not vary as much with changes in temperature, which may be an important attribute for a particular application. Happily, for what we are doing here, we really don’t have to worry about any of this. For the purposes of these columns, we are going to use the cheapest, most common resistors we can lay our hands on (I’ll guide you in this later).
Standard Resistor Values (a Little History)
As we will come to see in future columns, when we design an electronic circuit, we may perform some calculations, wave our hands in the air, perform an interesting dance, and decide that -- in an ideal world -- we would like to use a resistor with a value of exactly X ohms.
One solution would be to handcraft individual resistors with whatever values we wish, but this would be resource-intensive and time-consuming, to say the least. Alternatively, it would potentially be possible for resistor manufacturers to offer bespoke services where we tell them what we want and they build to order (BTO), but this would take lots of time and be tremendously expensive. Furthermore, neither of these options work well if the intention is to create large numbers of products with interchangeable parts.
What we really need is access to affordable, off-the-shelf resistors that are available when we require them. Unfortunately, the folks who manufacture resistors simply cannot create and supply every conceivable value in a cost-effective manner. And, even if every possible value was available, the people who use resistors couldn’t afford to purchase all of the different types and wouldn’t have the space required to store them if they did.
The solution arrived at by the industry was to adopt a selection of standard values, which had the added advantage of allowing users to second-source their resistors from multiple manufacturers. The real trick was for everyone to agree on the values forming the standard set.
Before we proceed, there’s an important topic we need to introduce, which is that of “tolerance.” In this context, tolerance refers to the limits of variation of a resistance...Read more »
09/01/2020 at 18:49 •
Supposing I were to tell you that I know three people: an average-sized kid, a regular-sized adult, and a beanpole of a basketball player. Let’s assume that, earlier today, I used my handy-dandy tape measure to determine that the kid is exactly 4-feet tall, the adult is 6-feet tall, and the basketball player is 8-feet tall.
Now, suppose I were to inform you that these three people are currently in close proximity to each other and they are all looking in the same direction. Assuming that there’s nothing to block anyone’s view, which of these characters do you think will be able to see the farthest?
Your initial reaction may be to choose the basketball player, but you are making a number of assumptions, not the least being that you are assuming all these characters are standing up. It might be that the adult is ensconced in a comfy chair while the basketball player is kneeling down, for example (you have to be careful discussing things with engineers because we can be tricky little scallywags if we want to be).
Even assuming that all three of our subjects are standing up, we still can’t guarantee that the basketball player has the advantage. This is because we haven't specified their relationship to each other, which could be as illustrated below.It's hard to compare things if you don’t first set the ground rules (Image source: Max Maxfield)
The thing is that it can be hard to compare things if we don’t first set the ground rules (no pun intended). In this case, for example, on the left, we find our 6-foot adult standing on the ground, which places his head six feet above ground level. In the middle, our 4-foot tall kid is standing on a 4-foot tall box, which results in his head being eight feet above the ground. Meanwhile, on the right, our unfortunate 8-foot tall basketball player finds himself standing in a 4-foot deep hole (I hate it when that happens), which leaves his head only four feet above the ground. The end result is that, in this scenario, it’s the 4-foot kid who can see the farthest.It’s important to establish a common frame of reference (Image source: Max Maxfield)
The point of all this is that it’s possible for us to measure people’s heights individually, but -- depending on what we are trying to do -- it may be meaningless to compare them with each other unless we first establish some common frame of reference. In the case of our three test subjects, for example, our original question -- “Which one will be able to see the furthest?” -- makes much more sense if we also specify that they are all to be standing close to each other on a level piece of ground as illustrated above, in which case the basketball player will, not surprisingly, have the advantage.
In earlier columns, we’ve introduced the concepts of voltage (measured in volts), current (measured in amps), and resistance (measured in ohms).
It may not surprise you to learn we have tools we can employ to measure these little rascals: we can use voltmeters to measure voltage, ammeters to measure current, and ohmmeters to measure resistance. We also have multimeters, which can measure voltage, current, and resistance, along with a variety of other things, depending on the meter.
In the early days (circa the late 1800s and early 1900s), all of these meters were analog in nature, using a moving pointer to display the reading. Later, digital meters with numeric displays arrived on the scene. Today, it’s possibly to purchase analog and digital versions of all these meters.
In a future column, we will talk about digital multimeters in more detail, including where to get them and how to use them to measure things. For the purposes of this column, however, let’s simply assume we have a digital voltmeter, which we can use to measure the voltage difference (more formally, the electric potential difference) between two points in an electric circuit.
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