{"id":3060,"date":"2019-03-26T17:16:40","date_gmt":"2019-03-26T21:16:40","guid":{"rendered":"http:\/\/www.circuitcrush.com\/?p=3060"},"modified":"2021-06-30T15:21:31","modified_gmt":"2021-06-30T19:21:31","slug":"electrical-filters-intro","status":"publish","type":"post","link":"https:\/\/www.circuitcrush.com\/electrical-filters-intro\/","title":{"rendered":"Intro to Electrical Filters"},"content":{"rendered":"<h1><strong>Intro to Electrical <\/strong><strong>Filters<br \/>\n<\/strong><\/h1>\n<h2><strong>So Many Electrical Filters, So little Time\u2026<br \/>\n<\/strong><\/h2>\n<p>Do an online search for the word <em>filter <\/em>and you\u2019ll get a ton of results ranging from car parts to coffee. This post, however, will focus on electrical filters.<\/p>\n<p>Even if we narrow our search down to the term <em>electrical filter, <\/em>we\u2019re still going to get a ton of results. After all, entire books have been written on electrical filters (I should know, I own one).<\/p>\n<p>That\u2019s because even in the realm of just electrical filters there are many different types.<\/p>\n<p>We have passive and active filters. Digital and analog filters. Filters bearing the name of their creator like the Butterworth filter, Bessel filter, and Chebyshev filter (don\u2019t ask me how to pronounce that). And there&#8217;s more.<\/p>\n<p><!--more--><\/p>\n<p>Since this is an introduction to electrical filters, we\u2019re going to keep it simple and talk about basic passive analog filters. We\u2019ll see a little bit of math, but leave the transfer functions, poles, zeros, Bode plots, and Laplace transforms to the engineering books and professors.<\/p>\n<h2><strong>So, What\u2019s a Filter?<br \/>\n<\/strong><\/h2>\n<p>Filters have been an integral part of electronics for a long time. In fact, several technological achievements wouldn\u2019t be possible without them.<\/p>\n<p>A filter is a frequency selective device. In other words, filters allow certain frequencies to pass through, but block others. They \u201cfilter out\u201d the frequencies we don\u2019t want.<\/p>\n<p>Another way to state this is that filters <em>attenuate<\/em> some frequencies more than others. By attenuate, we simply mean to reduce in amplitude. This has the effect of blocking signals we don\u2019t want while passing the ones we do.<\/p>\n<h2><strong>Passive vs Active Filters<br \/>\n<\/strong><\/h2>\n<p>Both of these electrical filter types are quite common. We won\u2019t go into any detail on active filters here, but let\u2019s quickly touch on the difference.<\/p>\n<p>Common <em>passive<\/em> filters are unpowered and consist of things like resistors, capacitors, and inductors.<\/p>\n<p><em>Active<\/em> filters use some sort of amplifier, usually an op-amp. Because of this, an active filter can have a gain greater than one while a passive filter has a maximum gain of one (a.k.a. <em>unity gain<\/em>). In reality, passive filters have a gain of less than one due to losses in the components.<\/p>\n<p>This article will focus on passive filters because they are simpler and easier to understand.<\/p>\n<h2><strong>Electrical Filter Lingo<br \/>\n<\/strong><\/h2>\n<p>Before we dive in and take a closer look at some basic filter types, it will be helpful to understand some common filter lingo.<\/p>\n<p>We now know that electrical filters attenuate and block certain frequencies while passing others, thus effecting the signal\u2019s amplitude. This is the filter\u2019s <strong><em>frequency response<\/em><\/strong>. The frequency response is usually given in a graphical form like figure 1.<\/p>\n<p>&nbsp;<\/p>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone wp-image-3061 size-full\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/Electrical-Filter.jpg\" alt=\"Low-pass electrical filters frequency response\" width=\"535\" height=\"383\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Electrical-Filter.jpg 535w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Electrical-Filter-150x107.jpg 150w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Electrical-Filter-300x215.jpg 300w\" sizes=\"(max-width: 535px) 100vw, 535px\" \/><\/p>\n<p><strong><em>Figure 1: frequency response of a low-pass filter.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>The figure above brings us to our next term: <strong><em>cutoff frequency<\/em><\/strong><em>. <\/em>This term has several aliases including <strong><em>corner frequency<\/em><\/strong>, <strong><em>3-dB point<\/em><\/strong> and <strong><em>half power point<\/em><\/strong>. Let\u2019s talk a bit more about the last two.<\/p>\n<p>First, if you\u2019re not sure what a decibel (or dB) is, check out <a href=\"http:\/\/www.circuitcrush.com\/the-decibel\/\" target=\"_blank\" rel=\"noopener noreferrer\">All About the Decibel<\/a> where you\u2019ll get some answers. If you already know this stuff, then keep reading.<\/p>\n<p>The horizontal red dashes represent the 3-dB point (a.k.a. cutoff frequency). This is frequency at which the output power of the filter drops about 3-dB (actually it\u2019s 3.01- dB, but we round it). A decrease in power of 3-dB cuts the output power in half, hence the other name &#8211; half power point. Another interesting thing to note about this point is that the output voltage drops to 70.7% of its original value.<\/p>\n<p>The filter\u2019s <strong><em>roll-off<\/em><\/strong> describes the steepness of the drop after the cutoff frequency. In a perfect world, a filter would have a totally vertical roll-off. In reality that never happens. Roll-off is given in dB\/octave (doubling of frequency) or dB\/decade (ten times the frequency).<\/p>\n<p>Filters also have an <strong><em>input and output impedance<\/em><\/strong>. To get the best performance, the filter\u2019s impedance should match that of the circuit it connects to.<\/p>\n<p>Anyone order a filter? Seriously, the filter\u2019s <strong><em>order<\/em> <\/strong>describes the number of RC or LC pairs in the filter. In general, higher-order filters have better performance and come closer the ideal vertical roll-off. Of course, filter design &#8212; like most things in life &#8212; is a series of trade-offs. Stacking several RC or LC pairs together to create an 18-th order filter not only totally complicates things, you also reach a point of diminishing returns.<\/p>\n<p>&nbsp;<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-3062 size-full\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/Second-Order-Filter.png\" alt=\"2nd orderelectrical filters\" width=\"591\" height=\"263\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Second-Order-Filter.png 591w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Second-Order-Filter-150x67.png 150w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Second-Order-Filter-300x134.png 300w\" sizes=\"(max-width: 591px) 100vw, 591px\" \/><\/p>\n<p><strong><em>Figure 2: a second-order low-pass filter. Notice there are 2 RC pairs.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<h2><strong>Basic Electrical Filter Types<br \/>\n<\/strong><\/h2>\n<h3><strong>Low-pass Filters<br \/>\n<\/strong><\/h3>\n<p>We\u2019ve already established that there are many, many types of filters, even if we limit ourselves to passive analog filters. Of the crowd, there are four basic types.<\/p>\n<p>Figure 1 depicts the frequency response of a <em>low-pass filter<\/em>. As you may have guessed, a low-pass filter passes low frequencies and blocks higher frequencies. An ideal LP filter would look more like a square or rectangle, but like we said before, there is nothing perfect in this world. Because of that, low-pass filters have a response that looks something like figure 1.<\/p>\n<p>Figure 3 depicts the actual circuit. Let\u2019s talk about that circuit for a minute.<\/p>\n<p>&nbsp;<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-3063 size-full\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/Low-Pass-Filter.png\" alt=\"Low-pass filter circuit\" width=\"250\" height=\"140\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Low-Pass-Filter.png 250w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Low-Pass-Filter-150x84.png 150w\" sizes=\"(max-width: 250px) 100vw, 250px\" \/><\/p>\n<p><strong><em>Figure 3: a basic low-pass filter.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>Capacitive reactance is inversely proportional to frequency. In other words, the higher the frequency the lower the reactance. At 0 Hz (DC) a capacitor is like an open circuit, so all the voltage appears across it. At slightly higher frequencies, most of the voltage drops across the capacitor due to its high reactance, thus passing low frequencies. This is because the capacitor and resistor form a voltage divider and at low frequencies the capacitive reactance is large compared to the resistance of the resistor.<\/p>\n<h3 style=\"text-align: center;\">Become the Maker you were born to be. Try <a href=\"https:\/\/learnarduinonow.com\">Arduino Academy<\/a> for FREE!<\/h3>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter  wp-image-4238\" src=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2.png\" alt=\"\" width=\"426\" height=\"162\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2.png 828w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2-300x114.png 300w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2-150x57.png 150w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2-768x292.png 768w\" sizes=\"(max-width: 426px) 100vw, 426px\" \/><\/p>\n<p>If you\u2019re unfamiliar with the term reactance, just think of it as a frequency dependent resistance.<\/p>\n<p>When the frequency increases, more voltage will drop across the resistor and the capacitor will start to behave more like a short circuit. Basic circuit analysis tells us that there is no voltage drop across a short circuit, thus there will be no output at higher frequencies. This is how a low-pass filter attenuates high frequencies.<\/p>\n<p>In case you care, the formula for capacitive reactance is given in equation 1. We can plainly see that it is frequency dependent and that the higher the frequency gets the lower the reactance gets.<\/p>\n<p>X<sub>C <\/sub>= 1 \/ (2\u03c0fC)\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 (eq. 1)<\/p>\n<p>Where f is the frequency and C is the capacitance.<\/p>\n<h3><strong>High-pass Filters<br \/>\n<\/strong><\/h3>\n<p>A <em>high-pass filter<\/em> does the opposite. It will block low frequencies and pass high ones. Figure 4 depicts a high-pass filter circuit.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-3064\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/High-pass-filter.png\" alt=\"High-pass electrical filters\" width=\"277\" height=\"158\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/High-pass-filter.png 210w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/High-pass-filter-150x86.png 150w\" sizes=\"(max-width: 277px) 100vw, 277px\" \/><\/p>\n<p><strong><em>Figure 4: a basic high-pass filter.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>At low frequencies the reactance will be high and almost all the input signal will drop across the capacitor. Because of this, low frequencies will be blocked. As the input frequency increases, the reactance decreases, allowing more of the input signal to pass through.<\/p>\n<p>A good way to remember the difference between the two circuits is by noting the position of the capacitor. In a low-pass filter the capacitor is in the lower position relative to the resistor, in a high pass-filter it is in the higher position relative to the resistor.<\/p>\n<p>Figure 5 gives the frequency response of a typical high-pass filter.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-3065 size-full\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/High-pass-Filter.jpg\" alt=\"High-pass-Filter frequency response\" width=\"583\" height=\"356\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/High-pass-Filter.jpg 583w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/High-pass-Filter-150x92.jpg 150w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/High-pass-Filter-300x183.jpg 300w\" sizes=\"(max-width: 583px) 100vw, 583px\" \/><\/p>\n<p><strong><em>Figure 5: high-pass filter frequency response.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<h3><strong>Band-pass Filters<br \/>\n<\/strong><\/h3>\n<p>A band-pass filter passes a certain band (group) of frequencies between a lower and upper cutoff frequency while attenuating others. To see what I mean, feast your eyes upon figure 6, which shows the frequency response of a band-pass filter.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-3066 size-full\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Pass-Filter-Frequency-Response.png\" alt=\"Band-Pass-Filter-Frequency-Response\" width=\"610\" height=\"361\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Pass-Filter-Frequency-Response.png 610w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Pass-Filter-Frequency-Response-600x355.png 600w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Pass-Filter-Frequency-Response-150x89.png 150w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Pass-Filter-Frequency-Response-300x178.png 300w\" sizes=\"(max-width: 610px) 100vw, 610px\" \/><\/p>\n<p><strong><em>Figure 6: band-pass filter frequency response.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>There are a few things to point out about the figure above.<\/p>\n<p>First, the bandwidth (in the darker color) is the frequencies that the filter passes. It is equal to f<sub>H <\/sub>minus f<sub>L<\/sub> and is dependent on the design of the filter. f<sub>H <\/sub>and f<sub>L <\/sub>are the high cutoff frequency and low cutoff frequency, respectively.<\/p>\n<p>Second, this filter has two 3 dB points or cutoff frequencies.<\/p>\n<p>Next, notice the labels on top of the picture. This filter has two stop-bands and a pass-band. More filter lingo.<\/p>\n<p>Finally, the <strong><em>slope<\/em><\/strong> is a synonym for the roll-off we talked about earlier.<\/p>\n<p>To make a band-pass filter, all you basically need to do is put a low-pass filter in series with a high-pass filter. Figure 7 illustrates this.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-3067 size-full\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Pass-Filter.jpg\" alt=\"Band-Pass-Filter circuit\" width=\"476\" height=\"286\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Pass-Filter.jpg 476w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Pass-Filter-150x90.jpg 150w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Pass-Filter-300x180.jpg 300w\" sizes=\"(max-width: 476px) 100vw, 476px\" \/><\/p>\n<p><strong><em>Figure 7: a simple band-pass filter consists of a low-pass filter in series with a high-pass filter. The output is taken across resistor R.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>For example, if we need to make a filter that passes frequencies from 10 kHz to 50 kHz, we can just put a 10 kHz high-pass and 50 kHz low-pass filter together.<\/p>\n<h3><strong>Band-reject, Band-stop or Notch Filter<\/strong><\/h3>\n<p>A band-reject (a.k.a. notch, band-stop) filter is the opposite of a band-pass filter. Its job is to reject a certain (usually narrow) band of frequencies while passing others. The reject band is often somewhere in the middle but doesn\u2019t have to be. Figure 8 illustrates the frequency response of a typical band-stop filter.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-3068 size-full\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/Band-Stop-Filter-Frequency-Reponse.gif\" alt=\"Band-Stop-Filter-Frequency-Reponse\" width=\"493\" height=\"277\" \/><\/p>\n<p><strong><em>Figure 8: band-stop filter frequency response.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>To build a notch filter (there goes more filter lingo\u2026) we need to gang a low-pass and a high-pass filter together in parallel.<\/p>\n<p>Taking our previous example, we can build a 10 kHz to 50 kHz stop-band filter by putting a 10 kHz low-pass and a 50 kHz high-pass in parallel. Figure 9 depicts the circuit of a simple notch filter.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-3069\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/band-stop-filter.png\" alt=\"band-stop-electrical-filters circuit\" width=\"444\" height=\"256\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/band-stop-filter.png 600w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/band-stop-filter-150x87.png 150w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/band-stop-filter-300x173.png 300w\" sizes=\"(max-width: 444px) 100vw, 444px\" \/><\/p>\n<p><strong><em>Figure 9: a simple band-stop or notch filter. It\u2019s a bit harder to visualize the connections, but the two filters that make it up are in parallel.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<h2><strong>Electrical Filters and Inductors<\/strong><\/h2>\n<p>Electrical filters can be made from RC, LC, or even RLC pairs.<\/p>\n<p>At this point, you may be asking yourself something like <em>where are all the inductors? <\/em>Or, <em>why do we keep using capacitors and not inductors?<\/em><\/p>\n<p>Some filters do use inductors. In fact, any of the four basic filter types can be made using inductors, though the circuit layout will be different.<\/p>\n<p>Consider the filters in figure 10.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-3070\" src=\"http:\/\/www.circuitcrush.com\/wp-content\/uploads\/RL-Filters-1024x576.jpg\" alt=\"RL electrical Filters\" width=\"676\" height=\"380\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/RL-Filters-1024x576.jpg 1024w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/RL-Filters-600x338.jpg 600w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/RL-Filters-150x84.jpg 150w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/RL-Filters-300x169.jpg 300w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/RL-Filters-768x432.jpg 768w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/RL-Filters.jpg 1280w\" sizes=\"(max-width: 676px) 100vw, 676px\" \/><\/p>\n<p><strong><em>Figure 10: RL filters.<\/em><\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>The main thing to notice is that the inductor is in the opposite position for a given filter than the capacitor. For example, part (a) shows a high-pass RL filter, but the notice the output forms across the inductor whereas in an RC high-pass filter the output forms across the resistor.<\/p>\n<p>Let\u2019s talk about why this is the case.<\/p>\n<p>Just as in RC filters, the inductor and the resistor form a voltage divider.<\/p>\n<p>But inductive reactance is proportional to frequency, unlike capacitive reactance. Because of this, the inductor drops less voltage at lower frequencies. If the input frequency is low, the inductive reactance will be low, so (in the case of a low-pass RL filter) the resistor drops most the voltage. Therefore, the output of a low-pass RL filter is taken across the resistor.<\/p>\n<p>When the frequency increases, the inductive reactance kicks in and drops most of the voltage, thus passing high frequencies.<\/p>\n<p>In case you care, the formula for inductive reactance is given in equation 2.<\/p>\n<p>X<sub> L<\/sub> = 2\u03c0fL\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 (eq. 2)<\/p>\n<p>Where f is the frequency and L is the inductance of the inductor.<\/p>\n<h2><strong>But Why Aren\u2019t RL Filters as Common?<br \/>\n<\/strong><\/h2>\n<p>We\u2019ve already alluded to the fact that RC filters are used more often then RL filters, though there are some applications where RL filters shine.<\/p>\n<p>The reason for this is that inductors are big, heavy, bulky items. They can also be expensive items.<\/p>\n<p>Capacitors &#8212; on the other hand, are light, small, easy to make and cheap. Therefore, you\u2019re more likely to use RC filters in your applications than RL filters.<\/p>\n<h2><strong>Everyone Needs an Electrical Filter<br \/>\n<\/strong><\/h2>\n<p>At this point you may be asking yourself how to pick the values of R, C, and maybe L.<\/p>\n<p>Volumes can (and have been) written on filter design, even if we just limit ourselves to passive analog filters.<\/p>\n<p>Being an introductory post, the point here is to cover the foundation for those who are new to filters or need a review of electrical filter basics. We\u2019ll cover more specifics on passive analog filter design in a future article. We\u2019ll also talk about active filters and even digital filters eventually in separate articles.<\/p>\n<p>Until then, comment and tell us about your level of experience with filters (any kind). Maybe you can help write the next article!<\/p>\n<h2 style=\"text-align: center;\">Become the Maker you were born to be. Try <a href=\"https:\/\/learnarduinonow.com\">Arduino Academy<\/a> for FREE!<\/h2>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-4238\" src=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2.png\" alt=\"\" width=\"828\" height=\"315\" srcset=\"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2.png 828w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2-300x114.png 300w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2-150x57.png 150w, https:\/\/www.circuitcrush.com\/wp-content\/uploads\/FB_Cover2-768x292.png 768w\" sizes=\"(max-width: 828px) 100vw, 828px\" \/><\/p>\n<a target=\"_blank\" href=\"https:\/\/www.drpeterscode.com\/index.php\"><img src=\"https:\/\/www.circuitcrush.com\/wp-content\/plugins\/dpabottomofpostpage\/apixel1x1.jpg\" ><\/a><table><\/table>","protected":false},"excerpt":{"rendered":"<p>Intro to Electrical Filters So Many Electrical Filters, So little Time\u2026 Do an online search for the word filter and you\u2019ll get a ton of results ranging from car parts to coffee. This post, however, will focus on electrical filters. Even if we narrow our search down to the term electrical filter, we\u2019re still going [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":3071,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[9,133],"tags":[134],"class_list":{"0":"post-3060","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-electronics","8":"category-filters","9":"tag-filters","10":"entry"},"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/www.circuitcrush.com\/wp-content\/uploads\/Electrical-Filter-1.jpg","_links":{"self":[{"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/posts\/3060","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/comments?post=3060"}],"version-history":[{"count":5,"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/posts\/3060\/revisions"}],"predecessor-version":[{"id":4275,"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/posts\/3060\/revisions\/4275"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/media\/3071"}],"wp:attachment":[{"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/media?parent=3060"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/categories?post=3060"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.circuitcrush.com\/wp-json\/wp\/v2\/tags?post=3060"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}