{"id":278,"date":"2016-08-05T23:18:29","date_gmt":"2016-08-05T23:18:29","guid":{"rendered":"http:\/\/martinvb.com\/wp\/?p=278"},"modified":"2016-08-06T20:49:15","modified_gmt":"2016-08-06T20:49:15","slug":"minimalist-low-pass-filter-library","status":"publish","type":"post","link":"https:\/\/martinvb.com\/wp\/minimalist-low-pass-filter-library\/","title":{"rendered":"Minimalist low-pass filter library"},"content":{"rendered":"

So, the other day I needed to compute some low-pass filters on the fly on an Arduino Mega. By “on the fly” I mean that the filters’ parameters would eventually be recomputed mid-operation, so setting some equation with static\u00a0const<\/strong>\u00a0<\/em>parameters would not cut it. Using a static filter, is, however, the most common application scenario. If that’s your\u00a0case – and I insist – tweak the sh*t out of your filter with a decent tool<\/a>\u00a0then just add it to your code. If, on the other hand, you need to update your filter dynamically (or if you’re just plain lazy to compute poles and zeros), then this is for you.<\/p>\n

I ended up putting together a minimalist library for that,\u00a0libFilter<\/em>\u00a0(github!<\/a>). Works with the Arduino IDE and as a regular C++ library (just uncommenting one #define<\/strong> does the trick).<\/p>\n

\"Using<\/a>
Using two filter instances on a signal from a load cell getting punched.<\/figcaption><\/figure>\n

For now it only implements low-pass filters based on \u00a0normalized butterworth polynomials<\/a>, but who knows what necessity might add to it next. Let’s take a look at some ADC filtering:<\/p>\n

#include <filters.h>\r\n\r\nconst float cutoff_freq   = 20.0;  \/\/Cutoff frequency in Hz\r\nconst float sampling_time = 0.005; \/\/Sampling time in seconds.\r\nIIR::ORDER  order  = IIR::ORDER::OD3; \/\/ Order (OD1 to OD4)\r\n\r\n\/\/ Low-pass filter\r\nFilter f(cutoff_freq, sampling_time, order);\r\n\r\nvoid setup() {\r\n  Serial.begin(115200);\r\n  pinMode(A0, INPUT);\r\n  \/\/ Enable pull-ups if necessary\r\n  digitalWrite(A0, HIGH);\r\n}\r\n\r\nvoid loop() {\r\n  int value = analogRead(0);\r\n  float filteredval = f.filterIn(value);\r\n  \/\/View with Serial Plotter\r\n  Serial.print(value, DEC);\r\n  Serial.print(\",\");\r\n  Serial.println(filteredval, 4);\r\n  delay(5); \/\/ Loop time will approx. match the sampling time.\r\n}<\/pre>\n
’til next time!<\/p>\n
P.S.:\u00a0<\/strong>I just can’t avoid letting this page eventually fall into temporary ostracism. Geez.<\/p>\n","protected":false},"excerpt":{"rendered":"
So, the other day I needed to compute some low-pass filters on the fly on an Arduino Mega. By “on the fly” I mean that the filters’ parameters would eventually be recomputed mid-operation, so setting some equation with static\u00a0const\u00a0parameters would not cut it. Using a static filter, is, however, the most common application scenario. If … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1,14,13],"tags":[],"acf":[],"_links":{"self":[{"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/posts\/278"}],"collection":[{"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/comments?post=278"}],"version-history":[{"count":8,"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/posts\/278\/revisions"}],"predecessor-version":[{"id":287,"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/posts\/278\/revisions\/287"}],"wp:attachment":[{"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/media?parent=278"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/categories?post=278"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/martinvb.com\/wp\/wp-json\/wp\/v2\/tags?post=278"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}