{"id":651,"date":"2026-03-15T22:05:00","date_gmt":"2026-03-15T22:05:00","guid":{"rendered":"https:\/\/copperfiction.com\/?p=651"},"modified":"2026-04-09T22:08:44","modified_gmt":"2026-04-09T22:08:44","slug":"040-nfc-temperature-logger","status":"publish","type":"post","link":"https:\/\/copperfiction.com\/index.php\/2026\/03\/15\/040-nfc-temperature-logger\/","title":{"rendered":"[040] NFC TEMPERATURE LOGGER"},"content":{"rendered":"\n
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The starting constraint was easy to state and hard to meet: a standalone temperature logger, smaller than a one-euro coin, with the longest possible battery life, and contactless data retrieval.<\/p>\n\n\n\n

The form factor forces brutal decisions from the start. No room for a large cell, no room for a conventional radio module, no room to afford ordinary standby consumption. Every microamp has to be justified.<\/p>\n\n\n\n

The STM32L031G6U3TR was the obvious pick. It’s one of the most compact STM32 microcontrollers available \u2014 UFQ package, 3\u00d73 mm \u2014 and it comes with the low-power modes needed to survive in very tight energy budgets. In stop mode with the RTC running, consumption drops to a few hundred nanoamps. On a small cell, that translates to months of autonomous operation.<\/p>\n\n\n\n

Temperature measurement is handled by an external sensor selected for its footprint and current draw. The micro wakes up on a timer, takes a measurement, timestamps it, writes it to storage, and goes back to sleep. As simple as possible on the logic side, as frugal as possible on the energy side.<\/p>\n\n\n\n

For data retrieval: NFC Mailbox. No permanent radio, no Bluetooth, no antenna burning current in standby. Bring a smartphone close, the NFC field partially powers the circuit, and the logged data is read directly from memory. Clean, instant, no dedicated battery needed on the reader side.<\/p>\n\n\n\n

This project is a good example of what “design under constraint” actually means in practice: every single decision is a negotiation between size, power, and functionality.<\/p>\n\n\n\n

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The starting constraint was easy to state and hard to meet: a standalone temperature logger, smaller than a one-euro coin, with the longest possible battery life, and contactless data retrieval. The form factor forces brutal decisions from the start. No room for a large cell, no room for a conventional radio module, no room to … 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":[123],"tags":[130,129,131,128],"class_list":["post-651","post","type-post","status-publish","format-standard","hentry","category-123","tag-low-consumption","tag-nfc-mailbox","tag-sensor","tag-stm32l031g6u3tr"],"_links":{"self":[{"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/posts\/651","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/comments?post=651"}],"version-history":[{"count":1,"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/posts\/651\/revisions"}],"predecessor-version":[{"id":653,"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/posts\/651\/revisions\/653"}],"wp:attachment":[{"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/media?parent=651"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/categories?post=651"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/copperfiction.com\/index.php\/wp-json\/wp\/v2\/tags?post=651"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}