Apple has not made it easy to let the iphone communicate with external devices. Basically, you need a jailbroken phone to do anything. This post covers the current state of serial communication on the iphone.
A succesful example of making an application that uses the serialport on the iphone is xGPS, which let you connect to an external GPS.
There are two sites that kept showing up when I looked at solutions for accessing the serial port.
One solution described on ohscope, uses the mobile terminal app available from Cydia, in combination with a serial comunication program called minicom. Basically it lets you open a serial connection and you can send and receive data using the terminal window.
For simple monitoring of input this might be all you will ever need, and it is relatively simple to get working.
The other solution on devdot, dating back to 2007, is a serial communication application written in C, which is still the example that shows up in different forums. There has been a few changes since 2007, when Iphone was on OS 1.x.
My main interest in getting serial communication working is that it would be very helpful for some of my mobile installations like the Wind-up birds, a network of mechanical woodpeckers, where a lot of the work is setting up a network between several xbee radio modems. It also involves climbing in trees, and it would be very convenient to have small controller/monitor app on my iphone, instead of using my laptop.
I also think it would work well with my dimsun dimmers, being able to control the lights remotely.
When searching for solutions, some projects show up which claim that “the iphone controls my RC car/my garagedoor” etc, but actually the iphone is communicating with a pc which then again communicates with an arduino. This is ok for protyping, but I want to get rid of the PC part (Actually there was a project in 2008 which uses iphone-xbee to control a rc-car. The instructions are in Japanese, and it was made using python I believe).
There are some promising work being done on making the built in bluetooth work as a bluetooth modem (something that Apple has blocked). Currently the BTstack is only able to read serial data. There is a demo app showing how a wii controller controls a model of the wii on the iphone. There is also the HumanAPI project which has made an interface for a pulserate sensor, based on the BTstack and a programming environment called PhoneGap.
Maybe sometime soon it will be possible to access the serialport on the iphone without jailbreaking it. In the openframeworks forum a new serial adapter for the iphone was mentioned.
The physical connection
To get access to the serialport you need some sort of adapter from the iphone connector. I got mine here, and sparkfun stocks a few different models. You can find an overview of the pinout at pinouts.ru.
The physical connection is the easiest part. You only need three connections from the Iphone: rx,tx and gnd. Optionally you could also use the +3.3v connector, making it possible to power up your device from the iphone. I do this with my xbee connector, but you need to be careful with this, as you might break the iphone if your device draws too much current. I haven´t found a reliable source for how much current you can draw, but have seen 80-100mA mentioned a few places. This works fine with the standard xbee, as it draws around 40mA. It would also work fine with a 3.3v based arduino, and also probably with the FIO (not sure how much current the combination of the xbee and atmega chip draws).
Using the xbee which runs on 3.3v I connect tx_iphone to rx_xbee, rx_iphone to tx_xbee, and gnd_iphone to gnd_xbee.
If you connect the iphone directly to an arduino running on 5v, you need to have a 1 k resistor between tx_arduino and rx_iphone.
approach 1: Serial communication using mobile terminal and minicom
Before getting started I recommend installing a very useful addition to the iphone software called sbsettings, available on Cydia, which basically is like a control panel for “hidden” features on the iphone. You can also install addons like syslog, which is very useful when debugging. The mobile terminal app is also very useful.
The instructions from ohscope are pretty clear.
You need to know how to SSH to the iphone from your computer. I use a combination of fugu and terminal on OSX, Putty should do the job on Windows. There is a good explanation on how to do this on a mac (and many other useful things) at hackthatphone.
It is much easier to configure minicom from a terminal on a computer than from the iphone terminal program. So I open terminal on my mac,
and enter ssh -l root 10.0.1.9 (ip of my iphone). The default password is alpine.
After I had updated my iphone to 3.1.2 I got an error message when trying to open minicom: “minicom cannot create lockfile. Sorry” This turned out to be a permission problem, so I navigated to /var and changed the permission so anybody could write to lock: chmod a+w lock.
Some useful links related to mobile terminal and minicom.
mobile terminal wiki
I found some of the gestures not to be working, so I ended up mainly using the keyboard for navigation.
basic minicom commands
approach 2: make an app that can read and write to the serial port
Preparing for development on the iphone
Last saturday NYCresistor hosted an introductory openframeworks workshop with Zach Lieberman, one the creators.
Basically openframeworks makes it much easier to do interesting audiovisual programming than if you would have to write the code in C++, by wrapping low-level code in easier to use methods and functions.
I was new to both xcode, openframeworks and C, so there was a lot of new things to dive into, but it definetly helps having a background from programming with Processing.
The neat thing with openframeworks is that it is crossplatform: It runs on osX, linux, windows and iphone. This was a perfect opportunity for me to move to step two: make my own serial communication program.
The drawback with writing code for the iphone is that you are supposed to pay $99 to be a developer. Since I am mainly interested in developing programs for using the serialport on my own phone I wasn´t so interested in paying for it. Fortunately there are ways around this, but it is rather complicated.
One way is to use the free toolchain.
I felt more comfortable using Xcode combined with openframeworks, so I searched for ways of making Xcode compile, install and debug to the iphone.
First of all, you need to register as a developer at apple and download the Iphone SDK.
Then you have to do some modifications to get around signing process. There are several ways of doing this, some of them extremely complicated. I think I found a good solution that is not too hard, and which works on iphone os 3.12 and xcode 3.21.
The basic instructions are found at the networkpx project blog. First you need to create a code signing certificate, and update your xcode target accordingly. If you only want to compile in xcode, it is very simple, you only need to change a few lines in a file (I found three places that should be changed, the instructions only mentions two).
To be able to install and debug it gets more complicated.
I used a combination of Appsync 3.1, available from hackulo.us repository on Cydia, and some of the instructions from the networkpx project blog. Basically Appsync makes steps 5-10 in the install-debug section unnecessary.
It is important to set the -gta flag in the options for your xcode project (found in the code signing section, other code signing flags).
Now I am able to use the iphone with xcode like a normal developer: I can run and debug on the iphone simulator, or install, run and debug on the iphone, which is very convenient when developing. Sometimes debugging from the iphone doesn´t work, then I activate syslog which creates a log on the iphone that I can read on my computer later.
Setting up the serial port
The port name is the first thing to know: /dev/tty/iap
The serial code itself is quite standard, so the example from devdot would probably still work, basically doing
fd = open(“/dev/tty.iap”, O_RDWR | O_NOCTTY | O_NDELAY);
to open the port.
Using openframeworks, I modified the oFserial example found in the mac distribution (this example is not in the iphone distribution).
the only thing I need to open the serial port using openframeworks is to specify portname and baudrate: serial.setup(“/dev/tty.iap”,9600);
In v0.60 of openframeworks for iphone, the iphone is not included in the serial library, so you need to manually add “|| defined(TARGET_OF_IPHONE” to each #if section in ofSerial.cpp which refers to osx and linux, so it would look like this:
#if defined( TARGET_OSX ) || defined( TARGET_LINUX ) || defined(TARGET_OF_IPHONE)
This will most likely be included in newer versions of openframeworks.
So, by modifying an existing serial code example I was able to compile and run the program but got an error saying that it was unable to open serial port.
After a hint on the GPSserial forum, I understood that my problem was related to permissions of the application. The application needs to be run as root.
I spent about two days learning about permissions and trying with setting different permissions, without any luck.
Why was I able to open the serial port via minicom and terminal and not from my application?
After some more research I discovered that in the early Iphone OS days, applications were installed as root, this was later changed as it could be a security risk. Maybe this is why the example from 2007 worked back then, because it was automatically installed as root?
Appstore apps are installed in a different location (/private/var/mobile/Applications) than Cydia apps like Terminal (/private/var/stash/Applications), and these places have different permissions. Xcode automatically installs programs in the appstore appsection, inside a folder with a long number as name, such as 03A7764B-DDE0-4A60-A56B-CF2ADBB0213F. So what would happen if I moved my app to the the other applications folder?
I was able to connect to the serialport!
There might be an easier way to move the application, but this is how I did it: The easiest way to find the folder installed by xcode is to find the last created folder in the /var/mobile/Applications folder. Open this folder, and just copy the yourapp.app to the desktop. Then delete the folder using ssh from a terminal program. If you are in the Applications directory the command would be: rm -r 03A7764B-DDE0-4A60-A56B-CF2ADBB0213F (replace with your own folder name). Copy your.app into the /var/stash/Applications, respring the springboard (using sbsettings) on your iphone and you should be set. If you need to install a new version of the app from xcode you need to first delete yourapp.app and respring the springboard or else you will receive an error when trying to install the app.
To show that it actually works I have made two simple demo videos showing serial input and output.