--- title: Building An Energy-Harvesting Business Card | daily.dev description: A hobbyist built a business card powered entirely by NFC energy harvesting rather than a coin cell, driving 21 Charlieplexed LEDs via a small microcontroller.... canonical: https://daily.dev/posts/building-an-energy-harvesting-business-card-24xhj77ql twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Building An Energy-Harvesting Business Card | daily.dev og:description: A hobbyist built a business card powered entirely by NFC energy harvesting rather than a coin cell, driving 21 Charlieplexed LEDs via a small microcontroller.... og:url: https://daily.dev/posts/building-an-energy-harvesting-business-card-24xhj77ql og:image: https://api.daily.dev/og/posts/24xhJ77qL.png og:image:alt: Building An Energy-Harvesting Business Card og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Building An Energy-Harvesting Business Card **[Hackaday](https://daily.dev/sources/hackaday)** · 2 min read · 0 upvotes · 0 comments ## Summary A hobbyist built a business card powered entirely by NFC energy harvesting rather than a coin cell, driving 21 Charlieplexed LEDs via a small microcontroller. The card uses a PCB trace antenna designed with STM's antenna inductance tools and an LLM-assisted KiCad script; tapping it against a phone's NFC reader animates the LEDs. Design files are published on GitHub. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How can you power an LED business card without a battery? An LED business card can be powered by harvesting energy from a phone's NFC reader instead of using a coin cell. The design uses a PCB trace antenna tuned with antenna inductance design tools, driving 21 Charlieplexed LEDs and a small microcontroller. Tapping the card against a phone's back triggers the LEDs to animate using only the harvested NFC energy. _Tinkerers exploring battery-free electronics can find more builds like this NFC-powered card on daily.dev._ ### What is Charlieplexing used for in LED projects? Charlieplexing is a wiring technique that lets a microcontroller control many LEDs using far fewer I/O pins than one pin per LED. In this business card project, 21 LEDs were Charlieplexed so they could all be individually addressed by a small microcontroller within the tight space constraints of a PCB the size of a standard business card. _Developers designing pin-constrained embedded projects can browse Charlieplexing techniques on daily.dev._ ## Similar posts on daily.dev - [2026 Green Power Challenge: NFC Powers Command Write And Wake Of MCU](https://daily.dev/posts/2026-green-power-challenge-nfc-powers-command-write-and-wake-of-mcu-l6wk7fdso) · Hackaday · 0 upvotes · 0 comments - [Using NFC To Power Devices Instead Of Qi](https://daily.dev/posts/using-nfc-to-power-devices-instead-of-qi-lk79ogxyq) · Hackaday · 0 upvotes · 0 comments - [Someone made a literal credit card-sized ESP32 computer, and so can you](https://daily.dev/posts/someone-made-a-literal-credit-card-sized-esp32-computer-and-so-can-you-b1x1lp4ln) · XDA Developers · 0 upvotes · 0 comments - [GitHub - KaiPereira/Overglade-Badges: NFC hackathon badges for the Overglade game jam in Singapore\!](https://daily.dev/posts/github---kaipereira-overglade-badges-nfc-hackathon-badges-for-the-overglade-game-jam-in-singapore--xvhkvxuo1) · Hacker News · 0 upvotes · 0 comments --- Tags: [#hardware](https://daily.dev/tags/hardware), [#embedded](https://daily.dev/tags/embedded) [View this post on daily.dev](https://daily.dev/posts/building-an-energy-harvesting-business-card-24xhj77ql) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Building An Energy-Harvesting Business Card","url":"https://daily.dev/posts/building-an-energy-harvesting-business-card-24xhj77ql","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/building-an-energy-harvesting-business-card-24xhj77ql"},"datePublished":"2026-08-31T20:29:12.007Z","dateModified":"2026-08-31T22:07:53.362Z","description":"A hobbyist built a business card powered entirely by NFC energy harvesting rather than a coin cell, driving 21 Charlieplexed LEDs via a small microcontroller....","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/59bf1bbabea5d28454dc0138acdb912b?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/59bf1bbabea5d28454dc0138acdb912b?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Hackaday","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Hackaday","logo":"https://media.daily.dev/image/upload/s--JhDfhy70--/f_auto,q_auto/v1767541814/logos/hackaday","url":"https://daily.dev/sources/hackaday"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/building-an-energy-harvesting-business-card-24xhj77ql","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"hardware,embedded","timeRequired":"PT2M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Hackaday","item":"https://daily.dev/sources/hackaday"},{"@type":"ListItem","position":3,"name":"Building An Energy-Harvesting Business Card"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/building-an-energy-harvesting-business-card-24xhj77ql#faq","mainEntity":[{"@type":"Question","name":"How can you power an LED business card without a battery?","acceptedAnswer":{"@type":"Answer","text":"An LED business card can be powered by harvesting energy from a phone's NFC reader instead of using a coin cell. The design uses a PCB trace antenna tuned with antenna inductance design tools, driving 21 Charlieplexed LEDs and a small microcontroller. Tapping the card against a phone's back triggers the LEDs to animate using only the harvested NFC energy. Tinkerers exploring battery-free electronics can find more builds like this NFC-powered card on daily.dev."}},{"@type":"Question","name":"What is Charlieplexing used for in LED projects?","acceptedAnswer":{"@type":"Answer","text":"Charlieplexing is a wiring technique that lets a microcontroller control many LEDs using far fewer I/O pins than one pin per LED. In this business card project, 21 LEDs were Charlieplexed so they could all be individually addressed by a small microcontroller within the tight space constraints of a PCB the size of a standard business card. Developers designing pin-constrained embedded projects can browse Charlieplexing techniques on daily.dev."}}]} ```