Resistors - The Learning Circuit

the following program is brought to you by element 14 the electronic design community where you can connect and collaborate with top engineers from around the world join now at element14.com hi and welcome back to the learning circuit where we learn about basic electronics today we're going to learn about resistors nearly every circuit you come across will contain resistors in a circuit diagram a resistor symbol looks like a zigzag line or sometimes an empty rectangle it typically has its value written next to it this will be a number followed by the ohm symbol the measurement for resistance the resistor symbol is reversible as resistors are nonpolar meaning they will function the same if hooked up in either orientation remember back to when we learned about Ohm's law in every circuit there is a balance of voltage current and resistance most electrical components require a certain voltage and current to function properly we can control the voltage and current in various parts of a circuit by adding resistors resistance in an electrical circuit is when a material prevents some or all of the electrical current from flowing through it converting that restricted energy into heat every material has some resistance in resistors this principle is used to create a controlled amount of resistance that can be used to regulate circuits [Music] resistors can be made of a variety of materials each of those having advantages and disadvantages over the others let's talk about some of those types carbon composite resistors are made by combining a conductive material usually finely ground carbon or graphite with a non-conducting material like ceramic these were once widely used but have been mostly replaced by more efficient and precise resistor types and while they are cheap to produce they are now often more expensive because of the lack of use carbon film metal film and metal oxide film are examples of thin film resistors thin film resistors are generally made by depositing a conductive material onto an insulating ceramic rod or substrate a laser trimmed pattern is cut into the film in order to increase its conductive or resistive path the resistance value is controlled by varying the thickness of the film thin film resistors are the most common type of through-hole resistors but this method is also used to create surface mount resistors they feature relatively high tolerances low temperature coefficients low noise and work well in high frequency applications another type called Sir Met or thick film uses a paste combining ceramic and metal designed to have the optimal properties of both materials they have good temperature stability low noise and good voltage ratings but low surge current properties this method is most commonly used to make potentiometers and surface mount resistors wire wound resistors are made with wire with higher than normal resistance this gives them a high level of reliability and comparatively low level of temperature coefficient making them well-suited to handle high powers given the size of the wire used to make them they tend to be quite large they are often used in circuit breakers or as fuses when selecting resistors for your circuit there are some characteristics you're going to want to consider there's another unit we haven't talked about in terms of Ohm's law power power is the rate at which energy is transformed into something else it's calculated by multiplying the voltage difference across two points by the current running between them it is measured in units of watts every resistor has a maximum power rating in order to prevent a resistor from overheating you want to make sure that the power across it is kept under that maximum rating best practice is to select a resistor size that is capable of dissipating two or more times the calculated power carbon resistors for example are commonly made in wattage ratings of 1/8 watt 1/4 watt 1/2 watt 1 watt and 2 watts generally speaking the larger the physical size of the resistor the higher its wattage rating a 1/8 watt resistor is much smaller than a 2 watt resistor when shopping for resistors you will likely see a percentage preceded by plus/minus this is the tolerance of the resistor being the accuracy of its resistance rating resistance tolerances can be anywhere from a few fractions of a percent up to twenty percent for example a 100 ohm resistor isn't necessarily always exactly 100 ohms if it has a tolerance of plus or minus 2% it could be anywhere from ninety eight ohms up to one hundred and two ohms resistor values are sorted by tolerance and arranged into standard resistor values known as the EU series each series is arranged so that factoring in their tolerances no two resistor values within that series would overlap the series tolerance then determines how many different values fit in a series each series is named for how many values fall between zero and 10 e six has six values between zero and ten and one of the lowest tolerances at 20% e 12 has a tolerance of 10% e 24 5% e 48 2% e 96 1% and e 192 has tolerance is lower than 1% some values exist in multiple series therefore you can have a 4.7 ohm resistor with a tolerance of plus or minus 20% 10% or 5% the plus side is depending on your circuit you don't necessarily have to have a resistor that's the exact value you want often you can get away with a resistor that's just close to your desired value each resistor has a rating for the maximum amount of voltage it can withstand without failing these are often high enough that if you're a hobbyist working with DC Circuit's you don't have to worry much about it but it's always good to make sure that the voltage rating is plenty high enough for the voltage you plan to use in your circuit temperature coefficient gives the amount of resistance change that occurs when the temperature of the resistor changes a resistor could be 100 ohms at room temperature but that value could change with a significant temperature increase or decrease earlier I mentioned that resistors limit current by converting some of it energy into heat if too much current is being passed through a resistor it can cause the resistor to heat up to the point where the value changes it behaves differently or it could even burn up completely this one's a little easier as stated before the size of the resistor is often relative to its power rating in watts if you need a resistor that can handle a lot of power you're likely stuck with a larger resistor but if you're working with low power circuits you have a lot more options SMD resistors have gotten so small that it's often not a question of how small of a resistor you can get but how small of a resistor you can solder to your board reliably when most people think of resistors this is usually what comes to mind they either look like this with leads or like this and our surface mount these are fixed value resistors but not all resistors have a fixed value some are variable most variable resistors have a maximum resistance and can be adjusted to have a resistance between 0 or near zero and their maximum resistance some respond to environmental stimuli such as flex sensors that Bend for sensing resistors that respond to pressure thermistors that respond to heat and photo resistors or LDRs that respond to light there are others still that respond to moisture gas and other environmental stimuli the most common variable resistors are potentiometers inside they have a band of resistive material the control shaft connects to a wiper that contacts the resistive band and rotates varying the amount of resistive material between the two leads it can act sort of like a dimmer switch when using a potentiometer remember to factor in Ohm's law if you adjust the resistance the voltage and current change accordingly careful not to accidentally overload your circuit another type of potentiometer is a trimmer pot also called trim pots or presets they are normally mounted on PCBs and adjusted by using a screwdriver they are meant for occasional tuning in calibration set it and forget it some are multi turn for higher resolution adjustment we use these in the Ben Heck show episode where we automated the LEDs on my star wars bb-8 Art's a trimmer pot was used to control the sensitivity of the photoresistor rheostats are similar to potentiometers except they are mostly constructed as wire wound resistors the wiper moves back and forth along the wire coil to vary the amount of resistance one thing we haven't talked about is the markings on resistors through-hole resistors have stripes and SMD resistors have numbers on them in a future video we'll cover how to read these markings to determine the value of the resistor while I didn't cover everything about resistors it should be enough to get you started if you'd like to share more about resistors or tell a story about that time you burned up a resistor post about it on the element14 community on element14.com /the learning circuit happy learning [Music]

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Keywords: electronics, hardware, gaming, hacking, mods, weekly, element14, tbhs, benheck, madison, wisconsin, maker, engineering, thelearningcircuit, tlc, stem_projects, resistors, schematics, ldr resistor, smd resistor, trimmer pots, photoresistor, potentiometer, thermistor, cermet, thick film resistor, carbon resistor, metal resistor, metal oxide resistor, thin film resistor, wire round resistor, variable resistor, fixed rate resistor Tags Tag your content to make it easier to find

Id: 3MkWZ38WY5U

Length: 9min 27sec (567 seconds)

Published: Wed Jul 25 2018