{"id":452,"date":"2016-05-27T09:11:18","date_gmt":"2016-05-26T23:11:18","guid":{"rendered":"https:\/\/mindbleach.com\/words\/?p=452"},"modified":"2016-05-27T09:11:18","modified_gmt":"2016-05-26T23:11:18","slug":"all-the-switches","status":"publish","type":"post","link":"https:\/\/mindbleach.com\/words\/2016\/05\/27\/all-the-switches\/","title":{"rendered":"All the Switches"},"content":{"rendered":"

I recently bought a heap\u00a0of these<\/a>\u00a0switches – small DPDT toggle buttons – for $0.07\u00a0ea.<\/p>\n

\"New-20PCS-Lot-7X7mm-7-7mm-6Pin-Push-Tactile-Power-Micro-Switch-Self-lock-On-Off.jpg_640x640[1]\"<\/a>

Quantity over Quality<\/p><\/div>These switches are not that large, the on<\/strong> vs off<\/strong>\u00a0height difference is only about a millimetre, and I hate to think what the\u00a0‘rated cycles’ or debounce graph looks like.
\nRegardless of their shortcomings, the prospect of\u00a0having some silly project use literally THOUSANDS<\/em> of switches on the cheap is\u00a0enticing.<\/p>\n

…but how to read them all?<\/p>\n

The Problem<\/h1>\n

First of all, forget ‘one I\/O\u00a0per switch’, it will not scale well.<\/p>\n

The most\u00a0common method to wire up many switches is in a matrix.
\nEach row uses\u00a0an I\/O, each column uses an I\/O, and pressing the switch connects\u00a0that row and column together.
\n16\u00a0switches need 8 I\/O, 64 switches need 16 I\/O, it scales well. (and with a demux on one side, even fewer are needed)<\/p>\n

\"Nobody<\/a>

Nobody can be told what the matrix is, you have to see it for yourself. (see above)<\/p><\/div>\n

However, switches are only simple electrical devices. When a switch is closed current can freely flow in either direction. If only one or two are closed, the patterns are unique.\u00a0As soon as three or more switches are closed, a simple matrix can no longer read the switches with certainty. For example, there\u00a0is no way to distinguish between these five switch\u00a0states:<\/p>\n

\"Which

Indistinguishable patterns – Which switch is which?<\/p><\/div>\n

The matrix option will\u00a0not\u00a0be able to read\u00a0all the switches.<\/p>\n

The Not-So-Great Solution<\/h1>\n

This is a common problem faced by designers. What is\u00a0the common solution?
\nA\u00a0diode can be placed next to each switch to allow current only in one direction.<\/p>\n

\"I've

I’ve got pain in the diodes down my left hand side…<\/p><\/div>\n

“What’s wrong with that?”<\/em> Well,\u00a0every<\/strong> switch needs a diode.
\nSo now there are twice as many parts on the board, and you’ve got to find space for them, pay for them, solder them in…not great at all.<\/p>\n

Other Solutions?<\/h1>\n

What other options are there?<\/p>\n","protected":false},"excerpt":{"rendered":"

I recently bought a heap\u00a0of these\u00a0switches – small DPDT toggle buttons – for $0.07\u00a0ea. These switches are not that large, the on vs off\u00a0height difference is only about a millimetre, and I hate to think what the\u00a0‘rated cycles’ or debounce … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12],"tags":[79,80,81,78],"class_list":["post-452","post","type-post","status-publish","format-standard","hentry","category-electronics","tag-button","tag-diode","tag-matrix","tag-switch"],"_links":{"self":[{"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/posts\/452"}],"collection":[{"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/comments?post=452"}],"version-history":[{"count":2,"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/posts\/452\/revisions"}],"predecessor-version":[{"id":458,"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/posts\/452\/revisions\/458"}],"wp:attachment":[{"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/media?parent=452"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/categories?post=452"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mindbleach.com\/words\/wp-json\/wp\/v2\/tags?post=452"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}