arduino to iphone connection using FSK, and other sound ideas

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Scott Cytacki

Apr 28, 2012, 8:51:13 PM4/28/12
to cc developers, org-concord-sensor
I just stumbled on this:

I think the arduino side is similar to this:

I didn't find the sketch that is needed to interface with that iphone app.

Sam had mentioned this type of approach when we were thinking about arduinos and browsers before. However it isn't currently possible to access the microphone from a browser.

Putting that aside though, it seems like it would be possible to make a very cheap temperature sensor which used the headphone signal as an input and sent the result to the microphone. It wouldn't require  a battery or any digital processing, just a thermistor with other analog components which would modify and return the input wave. Since the headphone is stereo the second input might be useful for calibrating especially if the modification by temperature is amplitude based.

I'm surprised this hasn't been tried, seems like it could made for less than a dollars worth of parts. It might take some experimentation to find the cheapest analog circuit that would modify the input in a easy to detect way. 


Scott Cytacki

Apr 29, 2012, 1:58:03 PM4/29/12
to, org-concord-sensor
On Sun, Apr 29, 2012 at 6:26 AM, Chad Dorsey <> wrote:
I doubt this is using the microphone – it's probably using the headphone jack only, as a modem.

By microphone I was referring to the microphone that is part of the headphone jack, the extra mic contact that is part of most modern headphone jacks. 
This is very effective, and provides power as well – this is the basis of the Project HiJack work from Michigan that we've been following:

The Project HiJack folks are kindred spirits and we've been hoping to find some ways to work with them more closely – in my view, this is the key to the cheap, ubiquitous probes we talk about frequently.

However, I'm not sure you can access the jack from the browser, as Scott has said. I do have s fully working HiJack probe and an iPod Touch with their app installed sitting on my desk – you can borrow it to check out if you want.

Right, no browser access at least not without plugins. However one of Stephen's goals is to make a sensor that is cheap enough to give out free at conferences. I think to do this currently we would have to sacrifice browser support on mobile. On desktops we can use java or flash to connect to the mic from a browser.

I do think there is a more simple (even cheaper) version of the HiJack approach that doesn't require powering a digital circuit.

Sam Fentress

Apr 30, 2012, 9:52:32 AM4/30/12
I found another interesting idea a week or so ago: using the Arduino as a USB keyboard connected to the iPad/iPhone, and sending data as key events.

This video and some of the text is in Japanese, but it's fairly understandable. It uses a USBKeyboard library for the Arduino, requires wiring up a second USB out, and connects through a USB-iPad camera connection dongle. More information is also available here.

I don't know if there's any rate-limiting factor on sending keyboard events to the iPad, but if they could be sent quickly enough we could encode the data as two-character strings to get the ten-bit precision the Arduino outputs.


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