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Comment by Samuel_Michon | Hacker News Reader

I like this idea, and I was about to back it, but then I read this:

"Q. What type of battery does the FloJack run on? A. The FloJack runs on a standard 3V lithium cr2023 battery. You can find these at any grocery or convenience store."

Apparently, the dongle isn't powered by the host phone. No details were given on how long the dongle lasts on one battery, but if it's shorter than several months, I don't think this solution will catch on.

This thing looks like a round version of the Square card reader, a dongle that also plugs into an iPhone's headphone jack but doesn't require its own power source. So what gives?

If the headphone jack doesn't provide enough power for the NFC reader, perhaps they should release one that connects to the Dock connector or Lightning connector instead. Which of course does mean they'll have to deal with Apple.

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Samuel, the power efficiency of the FloJack is first rate. The consumption per polling interval is ~10uAs. On a 250mAh cr2032, this works out to about 90MM polls. At the Android polling rate of 10Hz, the FloJack would last just over 3 months. Since FloJack's sleep mode kicks in when apps stop using it, we estimate typical usage patterns will allow upwards of a year of battery life.

If they sip power that well, a battery should be included. Make the user experience that much better.

A battery is indeed included with each FloJack. Thanks for the feedback, we'll add that to the KS project page.

The Square reader basically acts like a magnetic tape head, using the tape to modulate an audio signal being played out of the audio port, and feeding the modulated result back in. It's completely passive much like a typical microphone is.

This NFC business requires actually transmitting some sort of radio waves, which requires some actual energy, not just modulation. IIRC the iPhone's audio port can be parasitized for a bit of energy, but it's in the realm of tens of milliwatts peak.

That may have been true initially, but according to a Square employee I talked to the reader actually has a battery and encrypts the card number before sending it to the phone. Also, each reader has a unique key.

Square added the encryption in the dongles last year. This happened not long after Verifone cited the lack of encryption in an early 2011 FUD campaign against Square.

http://techcrunch.com/2011/04/28/square-to-beef-up-card-read...

Neat, I forgot that they changed the stuff later on. I suppose the fact that the new one requires a battery bolsters my overall point, anyway.

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