Saturday, October 4, 2014

Qi Portable Power Receiving

In light of the new Adafruit Qi Transmitter, I diagram how you would design a Qi power receiver system.

The diagram shows the transmitter and a small, thin receiver built into a credit card size device with a micro-USB jack.  The card-size receivers are actually rated about 100 milliamps greater (600 ma) than the regular Qi receiver coil, Adafruit 1901 (500 ma).

You can plug the receiver directly into something needing power but that juice will go away when the receiver gets more than 8 millimeters away from the transmitter. 

To keep your project powered when the receiver is not powered, you can use the Adafruit Powerboost 500 C to regulate power and provide "off-grid" power with an extra LiPo battery.  Power will be available to the project and charge the battery simultaneously when the receiver is near the transmitter.  When the receiver is moved away, the Powerboost relies on the battery with very little transient changes (to quote Ladyada: "we did this by engineering the heck out of it (the Powerboost)".

Applications


What can you do with a Qi system?  Let's see:

  • Obvious is cell phone and tablet charging (what Qi was designed for)
  • Recharging your projects without plugging them in.  This could include:
  1. Firewalker shoes and other wearables
  2. Electronic Stuffed Animals
  3. Prop accurate projects (where a USB jack would be "unsightly")
  4. ... and more

Another idea is transmission of power through a window.  Why would one wish to do this?  Many people live in rented spaces where holes through exterior walls are not allowed.  Or maybe a homeowner does not want a hole in their house.  Placing a Qi transmitter on the inside and a receiver outside, you can get your project powered outside.  Just be sure the glass space is 2 to 8 millimeters, more than 8 millimeters is outside the Qi spec.

What uses do you see for Qi powering your Maker projects?