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So I recently discovered that my phone, a Nexus 5, has Qi wireless charging capabilities. I was wondering if it is possible to make my own charging coil with 24/26awg wire that would look something like this (but without the driver circuit).

Then, I would use a micro controller/build my own circuit to drive it at the correct frequency with a DC to AC converter. I was wondering if this would work, how precisely I would have to make the coil, and if I am missing something about Qi charging completely. I ask this because there are very few internet resources on homemade Qi coils.

Photo of a commercial charger

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  • \$\begingroup\$ If you just want the circuits, It's possible to get them. Adafruit carries bare transmitter and receiver modules. Likely a lot better than trying to build your own. \$\endgroup\$ – Nathan J. Aug 20 '18 at 21:02
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The Qi wireless charging protocol involves a complicated communication handshake from receiver (target device) to transmitter in order to enable charging. It is not trivial and requires strict timing. You 100% could make your own coil and driving circuit but it would be an endeavor for the sake of bragging to do it. The standard is open but you need to be a member of the wireless power consortium to get full access. See http://www.low-powerdesign.com/article_TI-Qi.html for some details.

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    \$\begingroup\$ It's not bidirectional, actually! The load communicates to the charger by modulating its load; there's no backchannel. \$\endgroup\$ – duskwuff Mar 7 '17 at 2:18
  • \$\begingroup\$ @duskwuff i miss read the article, I have corrected that. It is still fairly complex. \$\endgroup\$ – Passerby Mar 7 '17 at 2:20
  • \$\begingroup\$ @duskwuff But this is only physical implementation detail, load modulation works as communication channel from device to charger with the protocol, logic and so. \$\endgroup\$ – Martin Mar 7 '17 at 7:47
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    \$\begingroup\$ Actually, it is bi-directional, at least at the device detection stage. If one to examine Texas Instruments Qi charger portfolio (bq50002a coil driver and decoder bq500511a), one might get ideas of how Qi operates. The charger sends some "ping", and expects a response. Still I am dumbfounded why someone would take such a challenge. The wireless charging was in the works for 10+ years, and probably accumulated several thousands engineer-years, resulting in fairly complicated mixed-signal processors. It is quite audacious to embark on this development alone. \$\endgroup\$ – Ale..chenski Mar 10 '17 at 4:10
  • \$\begingroup\$ @duskwuff Load modilation is the backchannel. \$\endgroup\$ – winny Nov 4 '17 at 17:47
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QI charging requires the coil to have certain electrical properties, and involves some active communications from the device to the charger. Simply powering the coil is unlikely to work properly.

Information on the QI standard is available at the Wireless Power Consortium web site. However, keep in mind that some information is only available to members; you may have a hard time finding enough information to create your own implementation.

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You can build your own without the full spec, just need the right parts...

The BQ500412 is at NRND state but Digi-Key still sells them.

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