Implementing Qi Inductive Charging Yourself

Inductive charging is a technology that has promised a lot, but hasn’t quite delivered on the promise of never needing to plug in your phone again. The technology behind it is surprisingly simple though, and [Vinod.S] takes us through it all with an ATtiny13-based example.

An inductive charger has to be clever in its operation, for if it were to operate continuously it would soon have more in common with an inductive hob and thus become a fire risk, so it has to be sure that a compatible device is resting upon it before it tries to transmit power. It achieves this by periodically sending out a pulse of power intended to wake any devices in contact with it, and the device responds with a serial data stream encoded onto the device’s field by modifying the resonance of the receiver tuned circuit. This is done by a pair of MOSFETs under the control of the ATtiny in [Vinod]’s device, resulting in a functioning inductive power receiver built on a piece of prototyping board and sporting a buck converter capable of supplying 5 volts suitable to charge a phone. You can find the code on GitHub and see it in action below the break.

This tech has made an appearance here before a few times, such as when a Qi charger was integrated into a Chromebook.

18 thoughts on “Implementing Qi Inductive Charging Yourself

  1. Something I’ve been curious about, would it be possible to have a Qi receiver coil etched onto a PCB? All of the DIY solutions I’ve seen use coils like the one in the video. I’m assuming it’s possible as phones tend to use a flex PCB for their receivers.

    1. I’ve seen a few PCB coil based Tx/Rx module sets on AliExpress and the like.

      Reckon it’s probably quite achievable, and follows the trend of PCB motor coils, and PCB Tesla windings!

  2. It is possible. But a 100KHz power receiving coil really demands a litz wire to reduce the skin effect which adds extra AC resistance which cannot be nullified.

    But yes it is possible, but cannot expect a higher current due to overheating of the PCB coil.

    1. That is only important if you need to pull a lot of current. Even than you can use silver plated copper. With the skin effect most of the current flow will be in the plating.

  3. i wonder why we don’t have optical chargers. some high powered leds and a solar cell operating in the same wavelength. most of the inefficiencies of solar cells come from the fact that they cannot use the entire spectrum. but this shouldn’t be a problem if they are wavelength matched with the leds. im also somewhat curious how such a system would compare with an inductive solution.

  4. I was wondering what keeps the qi charge pads from charging through materials like plastic cases for phones and is there a way to increase the power so that it would charge through plastic or rubber material?

  5. “but hasn’t quite delivered on the promise of never needing to plug in your phone again.”
    Not once since I was given my phone as a gift, thus its entire life, have I used the charging port.
    My portable power banks all have QI transmitters and receivers, so I don’t even need to plug them in either.
    The only thing lacking is the option to trickle charge overnight to prevent things from heating up too much, but I think that and the option to limit the battery’s range to 20-70% for the sake of device longevity should be standard practice on everything, not just devices with wireless charging.
    I give users the option in all my devices, charge twice as often but have the device last years longer etc. Why no-one else does it is beyond me.
    I’ll be very happy on the day I first see two cent charger IC’s with this option, but for now, I just use cheap uC’s.

  6. I’m confused by the opening line:

    > Inductive charging is a technology that has promised a lot, but hasn’t quite delivered on the promise of never needing to plug in your phone again.

    How has it not delivered? I have a QI pad next to my bed and at my desks and an adapter for my phone – I have not plugged my phone in once since then. I think that the promise is entirely realised.

    Sure, we could quibble on efficiency but that’s been a trivial concern to me and hasn’t impacted me, practically.

  7. I’ve had good luck hacking the thin glue-on Qi receivers that they sell for older iPhones. You can frequently find them for ~$3 on Amazon. Cheaper than you can usually get the parts for, and then tend to have thin, flexible PCBs, and labeled traces hiding inside. Along with the shielding material that I’d otherwise likely leave out if building my own.

  8. Impressive. The guy imitated Qi backscatter protocol on a microchip Attiny13 to extract continuous power of 1A at 5V. After reading the blog post I realised Qi is having such complicated communication between the coil for uninterrupted power flow. Nice work.

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