How Accelerometers Work - The Learning Circuit

the following program is brought to you by element 14 the electronics community where you can connect and collaborate with top engineers from around the world join now at element14.com presents hi and welcome back to the learning circuit in this video i'm going to talk about a device that's so useful you probably don't realize all of the things it's in it can be used to sense vibrations and movement detect free fall and determine orientation in three-dimensional space so let's learn about these fascinating devices accelerometers [Music] an accelerometer is an electromechanical device that converts mechanical force into electrical signals the forces they detect may be static like gravity or dynamic like sensing vibrations and movement to understand how accelerometers work we first have to understand what acceleration is we're used to measuring the speed of cars in miles or kilometers per hour measuring a distance traveled in a set period of time acceleration is the measurement of the change of speed over time distance and time are easy to measure so how do we measure the rate of change use the force luke [Music] that's right we need to consider force here we look at newton's laws of motion newton's first law states an object at rest or an object in motion will remain that way unless acted upon by a force this guy won't move until he is acted upon by a force and this will keep spinning until it is acted upon by a force the force of me flicking my finger will cause him to accelerate and the force of my finger touching the spinner causes it to decelerate to get the formula to calculate these forces we look at newton's second law of motion which states force equals mass times acceleration we want to measure acceleration so let's flip that around acceleration equals force divided by mass in other words acceleration is the amount of force we need to move each unit of mass so what forces are we talking about one constant force used in calculating acceleration is gravity acceleration is usually expressed in one of three units of measurement meters per second per second or meters per second squared a gal or galileo defined as one centimeter per second squared or in standard gravity measured in g's if you've seen any movies or documentaries about fighter jets or astronauts you've probably heard of geforce not that guinea pig movie and if you've been on a roller coaster carnival ride one of those old school playground merry-go-rounds or even just a swing set you've definitely felt it standard gravity is the nominal gravitational acceleration of an object in a vacuum near the surface of the earth usually denoted by g0 or gn meaning if all other forces are removed such as air which provides wind resistance standard gravity is the rate of acceleration at which an object would fall to earth 1g is equal to 9.80 meters or 32.2 feet per second squared a small g-force like less than 1g would show as a waveform with a small amplitude while a large g-force like eight g's would create a waveform with a much higher amplitude when looking at accelerometers you should see a g rating showing the full dynamic range the chip is capable of this adxl335 that is common with hobbyists has a set range of plus or minus 3 g's while this lsm 303 found in the bbc micro bit has multiple range options including 2 4 8 and 16 g's when in use one range value is selected notice on this chart the correlation between the measurement range and the sensitivity the 2g setting can only measure a small amplitude of signals but has a whopping 4096 counts per g a very high sensitivity the 8g setting can detect higher amplitude signals allowing a much larger range of detection however it only has 1024 counts per g a much lower sensitivity with a more sensitive setting the device can detect subtle changes in acceleration but since the range is limited any signals with too large an amplitude would get clipped or distorted use a larger range and the device can detect larger signals but sensitivity is sacrificed so larger range equals less sensitivity higher sensitivity equals a smaller detectable range so how do accelerometers detect g-force the types of accelerometers you will typically come across are either piezoelectric or mems how piezoelectric accelerometers work is a bit of science witchery this type has a crystal layer sandwiched between two electrodes the crystal is a structure made of positive and negative ions when force is applied the structure distorts the electrons of those ions shift around which generates an electric charge that charge is proportional to the force that is being applied so we can use it to measure acceleration the other and more common type is mems mems stands for micro electro mechanical systems these are microscopic mechanisms printed directly into ics within these systems there are sets of fingers or plates one set that is fixed and one that is spring-loaded and can move and respond to acceleration the interlocking fingers form a capacitance between them when the floating finger moves back and forth the distance between fingers changes increasing or decreasing those capacitances the system can detect these changes in capacitance and use that information to determine acceleration these measurements typically happen in one direction along a single axis however we often want to measure up to three dimensions or axes since mems accelerometers are printed directly into the substrate of ics multiple accelerometers can be printed together into one system or chip to measure multiple axes x y and z one for each direction a lot of the other integrated chips i've covered on the learning circuit so far are available in through-hole packages that can easily be placed on a breadboard for prototyping however accelerometers are quite complex so they tend to be surface mount only and are usually integrated into other systems or dev boards in some ics accelerometers are paired with a magnetometer compass and or gyroscope to detect up to six or nine axes these units are often called inertial measurement units or imus accelerometers are insanely useful they're so useful it's basically impossible to list all of their uses but here are a few they're used for orientation and movement control and video game controllers yeah they are how my diy vr system knows the movement of my head so how i navigate my smartwatch they're what tell my air pods to pause when i take one out of my ear they help keep jones and aircraft stable well i'm trying to explain to people what an accelerometer is i always use the example of a phone because that's something that they have on on them in their pocket and it's something that they've seen being used so when you're watching a video on youtube and you turn your phone sideways and youtube goes to landscape that's an example of an accelerometer in use so your phone has an accelerometer that knows when it's being tilted i actually use this in one of my videos so i get i use some javascript to get this data out so that i make a moving vr headset these devices are so small and so useful the possibilities are endless for what they could be used for so what ideas do you have whether you have a project in mind or just an idea that came to you i'd love to hear what you think about accelerometers post your thoughts and questions on the element14 community on element14.com forward slash the learning circuit happy learning [Music] you

Channel: element14 presents

Views: 20,771

Keywords: electronics, hardware, hacking, mods, weekly, element14, maker, engineering, element14presents, MEMS Electro-mechanical, G-force, Gravity, Piezoelectric, Electrode, Crystal, Newton’s Laws, Gal, Galileo, Standard Gravity, IMU, Vibration, Freefall, Orientation, Acceleration, Deceleration, Micro:bit

Id: 9WAckt2vrrQ

Length: 9min 15sec (555 seconds)

Published: Wed Sep 30 2020