{"id":1855,"date":"2015-11-28T22:57:55","date_gmt":"2015-11-28T20:57:55","guid":{"rendered":"http:\/\/saisa.eu\/blogs\/Guidance\/?p=1855"},"modified":"2015-11-28T23:03:09","modified_gmt":"2015-11-28T21:03:09","slug":"simple-led-detector-for-rfid-or-nfc-of-13mhz-without-any-battery","status":"publish","type":"post","link":"https:\/\/saisa.eu\/blogs\/Guidance\/?p=1855","title":{"rendered":"Simple LED detector for RFID or NFC of 13MHz, without any battery"},"content":{"rendered":"<p>Triggered by experience with &#8220;<a href=\"http:\/\/saisa.eu\/blogs\/Guidance\/?p=1841\">Raspberry and RFID reader\/writer, first test<\/a> &#8220;, I tested a simple LED RF detector idea that can be found in &#8220;<a href=\"http:\/\/www.instructables.com\/id\/RFID-Reader-Detector-Easy-to-Build\/?ALLSTEPS\">RFID detector<\/a>&#8221; and &#8220;<a href=\"http:\/\/www.instructables.com\/id\/RFID-Reader-Detector-and-Tilt-Sensitive-RFID-Tag\/?ALLSTEPS\">RFID Reader Detector and Tilt-Sensitive RFID Tag<\/a> &#8220;.<\/p>\n<p>For 13Mhz RFID\/NFC, the LED RF detector contains 3 components<\/p>\n<ul>\n<li>2uH inductance<\/li>\n<li>68pF capasitance<\/li>\n<li>low power LED<\/li>\n<\/ul>\n<p>The components are connected in parallel. The LC circuit has a resonance peak around 13 MHz and can drain enough power from the RFID\/NFC reader to light the LED. For simplicity, there is no resistor in the circuit that would limit the maximum current through the LED. The currents are so small that the resistor is not needed. The figure below is made with the <a title=\"Fritzing, tool for documenting Raspberry Pi projects\" href=\"http:\/\/saisa.eu\/blogs\/Guidance\/?p=1726\">Fritzing tool<\/a> .<\/p>\n<p><img loading=\"lazy\" alt=\"RF-detector-circuit2\" src=\"http:\/\/saisa.eu\/blogs\/Guidance\/wp-content\/uploads\/2015\/11\/rf-detector-circuit2-1.png\" width=\"600\" height=\"249\" \/><\/p>\n<p>The inductive coil of 2uH can be made by 7 loops of 25mm diameter. A functioning example is shown below. Capasitor is under the tape. The LED turns on around 15-20 mm above the RFID reader.<\/p>\n<p><img loading=\"lazy\" alt=\"RF-detector-LED3\" src=\"http:\/\/saisa.eu\/blogs\/Guidance\/wp-content\/uploads\/2015\/11\/rf-detector-led3.png\" width=\"600\" height=\"381\" \/><\/p>\n<p>The figure below shows a slight modification, where 2nd LED is added to the circuit. The 2nd LED is also parallel connected but with opposite direction than the 1st LED.<\/p>\n<p><img loading=\"lazy\" alt=\"RF-detector-LED1-smallest\" src=\"http:\/\/saisa.eu\/blogs\/Guidance\/wp-content\/uploads\/2015\/11\/rf-detector-led1-smallest.png\" width=\"595\" height=\"298\" \/><\/p>\n<p><strong>Online tools for calculating inductance of self made coils and resonant frequences<\/strong><\/p>\n<ul>\n<li>\n<div>Toolset 1<\/div>\n<ul>\n<li>\n<div><a href=\"http:\/\/www.pronine.ca\/coilcal.htm\">Single-Layer Air Coil Calculator<\/a> (mm or inches)<\/div>\n<\/li>\n<li>\n<div><a href=\"http:\/\/www.pronine.ca\/lcf.htm\">LC Tuned Circuit Calculator<\/a><\/div>\n<\/li>\n<li>\n<div><a href=\"http:\/\/www.pronine.ca\/qbw.htm\">Resonant Circuit Quality Factor and Bandwidth Calculator<\/a><\/div>\n<\/li>\n<\/ul>\n<\/li>\n<li>\n<div>Toolset 2<\/div>\n<ul>\n<li>\n<div><a href=\"http:\/\/www.daycounter.com\/Calculators\/Air-Core-Inductor-Calculator.phtml\">Air Core Inductor Inductance Calculator<\/a> (in inches)<\/div>\n<\/li>\n<li>\n<div><a href=\"http:\/\/www.daycounter.com\/Calculators\/LC-Resonance-Calculator.phtml\">LC Resonance Calculator<\/a><\/div>\n<\/li>\n<li>\n<div><a href=\"http:\/\/www.calctool.org\/CALC\/eng\/electronics\/RLC_circuit\">RLC circuit<\/a> with resonant frequency and bandwidth<\/div>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><strong>Portable tool for RLC circuit resonance frequency and bandwidth<\/strong><\/p>\n<p>One can use the portable <a href=\"http:\/\/www.miscel.dk\/MiscEl\/miscel.html\">MiscEl<\/a> tool to see the impact if the L or C values are changed. The screenshots below are for the used values L=2uH and C=68pF.<\/p>\n<p><a href=\"http:\/\/saisa.eu\/blogs\/Guidance\/wp-content\/uploads\/2015\/11\/miscel2.png\"><img loading=\"lazy\" alt=\"MiscEl2\" src=\"http:\/\/saisa.eu\/blogs\/Guidance\/wp-content\/uploads\/2015\/11\/miscel2-small.png\" width=\"300\" height=\"236\" \/><\/a> <a href=\"http:\/\/saisa.eu\/blogs\/Guidance\/wp-content\/uploads\/2015\/11\/miscel1-1.png\"><img loading=\"lazy\" alt=\"MiscEl1\" src=\"http:\/\/saisa.eu\/blogs\/Guidance\/wp-content\/uploads\/2015\/11\/miscel1-1-small.png\" width=\"300\" height=\"236\" \/><\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Triggered by experience with &#8220;Raspberry and RFID reader\/writer, first test &#8220;, I tested a simple LED RF detector idea that can be found in &#8220;RFID detector&#8221; and &#8220;RFID Reader Detector and Tilt-Sensitive RFID Tag &#8220;. For 13Mhz RFID\/NFC, the LED &hellip; <a href=\"https:\/\/saisa.eu\/blogs\/Guidance\/?p=1855\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[68,74,67,34,80,82,6,51],"tags":[],"_links":{"self":[{"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=\/wp\/v2\/posts\/1855"}],"collection":[{"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1855"}],"version-history":[{"count":1,"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=\/wp\/v2\/posts\/1855\/revisions"}],"predecessor-version":[{"id":1856,"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=\/wp\/v2\/posts\/1855\/revisions\/1856"}],"wp:attachment":[{"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1855"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1855"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/saisa.eu\/blogs\/Guidance\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1855"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}