On Fri, Oct 31, 2014 at 8:20 AM, Mik Lamming <mik@lamming.com> wrote:

Nordic announce support of some near-field charging standard.

I don’t understand what Nordic have done.

On Fri, Oct 31, 2014 at 8:56 AM, David Carkeek <dcarkeek@gmail.com> wrote:

There are a bunch of new things in this press release so I don’t understand it either. They say “magnetic resonance” and “spatial freedom” but then talk about pads and surfaces as though the device has to be resting on the surface. It s says “Out of Band” which I don’t understand and “up to eight devices”. Why couldn’t it be nine devices? Why do you need an SDK to make a charging system?

What I kind of think is that there a pad which is a kind of transmitting antenna that emits a signal to which a device resonantly couples over a distance that is not zero for the purpose of transferring energy for battery charging. Each device needs a channel (up to 8 are possible). That would be super cool if true. Need to read about Rezence. I might be completely wrong.

“The nRF51 Wireless Charging SDK is available today on a limited basis to lead customers.”
but “Engineering build of S120 and an updated nRF51 SDK is available today as a download for existing customers of nRF51822.”

Whom do I ask for the link? Not that I would know what to do with it after downloading.

On Fri, Oct 31, 2014 at 10:46 AM, Mik Lamming <mik@lamming.com> wrote

Following up on I’m assuming that the range is at best centimeters because it is near-field which drops off dramatically after a few wavelengths… doesn’t it?  The frequency is 6.8MHz, so the wavelength is ~5cms?  (Wrong 44.1 meters)

Aha…  I found this.
http://en.wikipedia.org/wiki/Rezence_(wireless_charging_standard)  which contains this useful information sentence:

The interface standard supports power transfer up to 50 Watts,[1] at distances up to 5 centimeters.[2] 

I also found this excellent video, the first 2-3 minutes of which gave me a strong intuitive sense of the characteristics.  https://www.youtube.com/watch?v=r1UT4NuygmQ

On Fri, Oct 31, 2014 at 11:29 AM, David Carkeek <dcarkeek@gmail.com> wrote:

Too bad it doesn’t work across a room, but still quite interesting. I watched about 5 minutes but I’ll have to finish it later.

I’m somewhat ashamed to say I don’t know much about RF fields, near-field, and the relationship of wavelength to power transfer. The wavelength of 6.8 MHz is 44 meters according to the calculator. I wonder why that frequency was chosen. It must mess pretty badly with nearby radios.
Tesla coil can work at tens of feet, maybe hundreds of feet.

On Fri, Oct 31, 2014 at 13:59 AM, Mik Lamming <mik@lamming.com> wrote

It’s only yhe first 5mins that are worth the time. The rest got out of my depth anyway. It just gave me a good feel for the strengths and weaknesses of near-field.

Ah MHz, not GHz! Yes – I agree. Doh.  Good job you check all my math.

c = 300,000 = 3 * 10^5 kms/s = 3*10^8 m/s
6.8 MHz = 6.8 * 10^6Wavelength = (3*10^8) / (6.8 *10^6) = 44.1mIt’s only the first 5mins that are worth the time. The rest got out of my depth anyway. It just gave me a good feel for the strengths and weaknesses of near-field.

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