{"id":679,"date":"2024-03-02T21:57:21","date_gmt":"2024-03-02T17:57:21","guid":{"rendered":"https:\/\/www.jrtwine.com\/blog\/?p=679"},"modified":"2024-04-02T07:12:49","modified_gmt":"2024-04-02T03:12:49","slug":"quadrature-encoding-refresher","status":"publish","type":"post","link":"https:\/\/jrtwine.com\/blog\/quadrature-encoding-refresher\/","title":{"rendered":"Quadrature Encoding Refresher"},"content":{"rendered":"

Quadrature Encoding<\/h1>\n

…is the method used by mechanical mice, trackballs, and spinners like those used on Tempest<\/em> and Arkanoid<\/em>.\u00a0 It works by attaching a movement axis to a slotted wheel and placing the slots in between two optoisolators or optos<\/em>.\u00a0 When talking about Quadrature Encoding, the two signals from the optos are sometimes referred to as Clock<\/strong> <\/span>and Data<\/strong><\/span>.<\/p>\n

<\/p>\n

(So I was looking at a device that converted trackball inputs into\u00a0 analog\/counter data and I thought it might be a good idea to write a quick refresher on what quadrature encoding is.)<\/p>\n

As the slots move through the optos it causes a repeating pattern of pulses.\u00a0 Since two optos are used, one gets broken<\/em> before the other.\u00a0 \u00a0 This means that one will pulse high before the other (or one will “lead” the other) depending on the direction the wheel is rotating.\u00a0 This results in predictable, deterministic behavior: in one direction, Clock<\/strong> <\/span>will generate a pulse before Data<\/strong><\/span>.\u00a0 In the other, Data<\/strong> <\/span>will generate a pulse before Clock<\/strong><\/span>.<\/p>\n

\"Quadrature<\/a>
Quadrature Pulses<\/figcaption><\/figure>\n

In the above image, the top waveforms show an example where the Clock<\/strong> <\/span> signal pulses high before the Data<\/strong><\/span> signal does, and the pattern repeats in a monotonous fashion.\u00a0 The bottom waveforms show the opposite where the Data<\/strong><\/span> signal pulses high before the Clock<\/strong> <\/span>signal does.<\/p>\n

Another way to think about it is to sample the Data<\/strong><\/span> signal at the rising edge of the Clock<\/strong> <\/span>signal.\u00a0 At the time Clock<\/strong><\/span> goes high, the Data<\/strong><\/span> signal will either be low<\/em> <\/span>or high<\/em><\/span>, and that determines the direction of travel.\u00a0\u00a0Some simple pseudocode for the geeks:<\/p>\n

when Clock<\/span> <\/strong>\r\n  \u00a0 direction<\/em> := Data  <\/span> <\/strong>\/\/ 1\/High or 0\/Low<\/span><\/pre>\n
So when you think about it, is it rather simple and only requires two signal (or GPIO) lines.\u00a0 And there you have it<\/strong><\/em> — a simple description on quadrature data and how to use it.<\/p>\n","protected":false},"excerpt":{"rendered":"
Quadrature Encoding …is the method used by mechanical mice, trackballs, and spinners like those used on Tempest and Arkanoid.\u00a0 It works by attaching a movement axis to a slotted wheel and placing the slots in between two optoisolators or optos.\u00a0 When talking about Quadrature Encoding, the two signals from the optos are sometimes referred to […]<\/p>\n","protected":false},"author":2,"featured_media":680,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,9],"tags":[],"class_list":["post-679","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-repair-logs","category-atari"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t