When I first saw this thing it seemed pretty obvious (wish I’d thought of it) but I don’t get the technical aspect of it using the headphone audio jack instead of the data-port. This just seems so counter-intuitive to me, not to mention ass-backwards. Isn’t the audio jack strictly analog? Does this Square thing have a modem chip in it to modulate/demodulate audio into data? Why would it work this way? It can only work with a smartphone (iPhone or Android) and they all have data-ports, so what’s the deal?
I’ve looked online but haven’t found any technical info on it.
I don’t know this for sure, but I would guess it’s so that it would fit different phones and devices. An Iphone only has two spots, and the only one it has in common with other devices is a headphone jack.
This.
It’s universal - all phones support a standard mic-input headphone jack. The data rate is so low that the phone can do the A/D demodulation in software trivially.
Isn’t the strip on a creditcard analog? It looks like the same general technology as a cassette tape to me. If so it would seem to be less expensive to get a analog reader only then have an analog to digital converter onboard, especially when there is already an a to d converter in the iDevice.
On the iOS platform, a developer needs to pay a licensing fee to Apple in order to sell hardware that interfaces with the Dock Connector (which only exists on Apple hardware).
By using the headphone jack, Square is able to avoid this expense and produce a single product that will work both on iOS devices, on Android devices, and on other platforms.
Also, the headphone jack is fairly universal and unlikely to change in the future. Anyone who knows Apple well knows that they have a tendency to implement new hardware without very much warning.
The headphone jack may also be better-suited to powering the reader. Headphone jacks are meant to power external devices - my headphones don’t have a battery in them, after all. I’m not sure the same is true of the dock connector.
Headphone jacks (for audio) do not provide power. Your headphone does not need power to generate sounds if it’s a dynamic output device. If you fed power to such a device, it would blow up, not with a bang, but with a whimper.
The jack socket on an iPhone (and Android phones, too) is TRRS (tip/ring/ring/sleeve). This is to provide Stereo output and mic input (for a handsfree headset). The mic line provides a small DC offset (2.7V, apparently) for condenser capsules and typical headset control circuitry (play/volume/dial/answer).
Of course headphone jacks provide power. Conservation of energy and all that. It’s in the form of an AC waveform instead of DC, but it’s power nevertheless.
I don’t know exactly how the Square reader works, but even if the DC bias that **si_blakely **mentioned didn’t exist, sending a 1 kHz waveform and having a rectifier+capacitor on the other end would provide more than enough power for a small device like that.
It comes off the magnetic read head as an analog waveform. That this waveform encodes ones and zeros doesn’t make it digital. What makes it digital is the circuit that decides which parts of the waveform represent ones, and which represent zeros…and in this case that can be the A-D converter inside the phone.
This is exactly true. My company develops accessories for the iPad and iPhone. If I remember correctly, using the dock connector would add somewhere from $7 to $10 to the retail price of a product as opposed to using the audio jack. Most of that goes to licensing, but the actual 30 pin connector costs quite a bit more as well.
Going against the grain here, but I’m going to say it’s because the headphone jack is at the top of the device, and easily reachable by a payer, while the data port (or whatever Apple calls it) is at the bottom-center of the device and would require the payee to hand over the device to the payer to swipe their card, or at the very least twist it so they can see the screen.
Of course the licensing fee probably applies as well.
Why not use the headphone jack?
a) It’s universal (all smartphones have one).
b) It’s at the top, making it much easier to use.
c) It doesn’t require any licensing fees or expensive connectors.
d) The interface electronics are really cheap.
The real question is, when is Square going to release a Chip-and-PIN card reader so that the rest of us can use it? (I understand that iZettle is Chip-and-PIN. And it uses the docking port.)
I always assumed that the Square is really a TTY device, which would be a fairly easy way to transfer data over the headset jack. But I’ve never really checked.
I guess I could take one into the office and bring it to the audio lab…
I tried to record it as audio in Windows, but I probably don’t have the pins right or something (it has 3 black stripes instead of 2 for a regular computer mic).