I uploaded a new sample sketch for my iPodSerial library that uses the Wii Nunchuk to control the iPod. I used todbot’s WiiChuck adaptor to connect the Nunchuk to the Arduino.



The Wii Nunchuk has a joystick, from which you can read the X and Y axes, a Z button, a C button and the 3-axis accelerometer. I mapped the controls so that: left/right on the joystick is skip forward/backward; up/down on the joystick is scroll up/down; Z button is Play; c button is Ok/Select; and a tilt backward (using the Y axis of the accelerometer) is the menu button.

You could of course map them any way you wanted to.

Here’s a quick video of it in action (the Arduino is off-screen to the right).

iPod arduino electronics wiichuck

Today we’ll look at one of the example sketches that comes with my iPod Serial library. This one is for the Simple Remote mode, aka iPod Remote mode, aka Mode 2. Simple Remote mode provides serial commands that are the equivalents of the commands available through the physical buttons on the iPod. For the nitty gritty see the protocol wiki page on ipodlinux.org.

The SimpleRemote_with_Bounce example sketch sends the Play/Pause message when it sees a button is down and sends the “button released” message when it sees the button is up. This is the sketch I used in my own remote.



This sketch uses the Arduino Bounce library to debounce the button. There’s a version that does the debouncing on its own, called SimpleRemote, but it’s more complicated and wouldn’t scale if you were to use it for more buttons.

Let’s take the example sketch line by line (mostly):

Line 7 pulls in the Simple Remote mode header file from the library. You need to have placed a copy of the iPodSerial library in your Arduino IDE’s libraries folder for this to work.

Line 8 pulls in the Bounce library. You need to have placed a copy of the Bounce library in your Arduino IDEs libraries folder for this to work.

Line 10 says we’re going to have our button connected to the Arduino’s digital I/O pin 5.

Line 11 sets the debounce interval to 20 milliseconds, meaning that the button has to stay up or down for 20 milliseconds before the Bounce library will decide that is really up or down.

Line 13 creates our Bounce object, which is what’s going to do the debouncing for us.

Line 14 creates our SimpleRemote object, which is what’s going to talk to the iPod for us.

Line 18 makes digital I/O pin 5 an input, so we can read from it to see if the button is up or down.

Line 21 enables digital I/O pin 5’s internal pull-up resistor. This sounds scary, but all it means to us is that we can connect a button between pin 5 and ground without any other circuitry, which is referred to as an active-low configuration. The means that the pin will read as LOW when the button is down (pressed) and HIGH when the button is up (released). That probably seem backwards but as long as we’re expecting it to work that way it’s not a problem.

Line 23 takes care of setting up the serial connection to the iPod.

Line 28 lets the SimpleRemote object take care of anything it needs to do with the iPod. This needs to be in our loop() function.

Line 30 asks our Bounce object if there has been a change in the state of the button. That is, has the button just been pressed or just been released.

Line 32 checks the new state of the button, now that line 30 has told us the button has just changed state. If the new state is LOW that means the button has just been pressed (since we’re using an active-low button configuration).

Line 34 will get executed if the button has just been pressed. It tells our SimpleRemote object to send the Play command, which toggles the iPod between Play and Pause, just like the physical Play / Pause button would.

Line 37 will get executed if the button has just been released. The Simple Remote protocol requires this so that the iPod knows when the button has been released. Because of this, press-and-hold behaviours of the physical buttons also work through Simple Remote mode. So, for example, if you press and hold the button using this sketch the iPod screen will fade to black after a few seconds, just like it would if you pressed and held the physical Play button.

And that’s it!

If you look in the library at the file SimpleRemote.h you can see the full list of commands that can be sent:

• Play (the one we used in the example, that toggles between Play and Pause)
• Volume Plus
• Volume Minus
• Skip Forward
• Skip Backward
• Next Album
• Previous Album
• Stop
• Just Play (rather than toggling between Play and Pause)
• Just Pause (rather than toggling between Play and Pause)
• Toggle Mute
• Next Playlist
• Previous Playlist
• Toggle Shuffle
• Toggle Repeat
• iPod Off
• iPod On
• Menu
• Ok / Select
• Scroll Up
• Scroll Down

Expanding the example to work with more buttons is pretty simple. Let’s see what it would look like if we added volume plus and minus button support:

iPod arduino electronics

3/26/2010 UPDATE: Advanced Remote mode is not working for me with iPhone. See update post.
4/14/2010 UPDATE: See here if you have a v1.4 PodBreakout board.

I had been using my iPod remote for a few months. It worked well and scratched the itch it was built to scratch. But in December I got a new car with iPod and Bluetooth integration. I also got rid of my despised Blackberry and switched to an iPhone. This meant I no longer needed to use my custom remote, so I placed it lovingly in my electronics drawer and forgot about it for a while.

Recently I was asked if I would present a talk at Make: PGH about my experiences developing my Arduino iPod Serial library. I agreed, and it’s tentatively scheduled for the April meet-up. Someone also sent me an email asking for some help troubleshooting their build of a remote, so I was inspired to dig the remote out of the drawer. I also took a look at the library I’d created and decided that I really ought to finish what I’d started.

I already had a spare logic-level converter and PodGizmo from the original project, so I soldered them together and hooked them up to my Mega. (The Mega is great for testing serial protocol stuff because it has four real serial ports, compared to the one on a regular Arduino. I built the library with debug hooks in it so that I could spit out the protocol data going back and forth between the iPod and the Arduino, and without that it would have been really hard to debug it.)

I discovered that the resistor connected to pin 21 isn’t needed. I also realized that I could use the iPod to supply the low-voltage power to the logic-level converter. This cleaned up the wiring considerably (click on the image to go to Flickr where there’s a full-resolution version):



On the left is a Freeduino with an Ethernet Shield on top of it, but more on that later - the point is that you just need 5V, Ground and your Serial TX/RX lines on the Arduino side. The awful connections in the four wires between the logic-level converter and the PodBreakout board shouldn’t be there. They only exist because I tried out the suggestion here to skip the logic-level converter and put a 1KOhm resistor between the Arduino TX pin and the iPod RX pin. I verified with an EE friend that this would be okay and he said:

While not optimal, you should never see a problem with a 1k resistor. On TX_ARDUINO... (not RX_ARDUINO). What you're doing is relying on the protection diode of the iPhone to clamp the Voltage and sink some current. The resistor will do two things. 1) Limit the current possible to send into the iPhone (5V / 1k = 5mA max). Almost all digital protection circuits can handle 5mA for a few minutes at least. Therefore, even if you wire it up wrong, you will be very unlikely to fry anything. 2) Provide somewhere besides the protection diode in the iPhone to dissipate the power (V^2/R = 1.7*1.7/ 1k = 2.89 mW). 3mW isn't a lot of power for a diode, but it will help prevent the chip from wearing out prematurely.
Vih on the ATmega328 (Duemilanove) is 0.6*Vcc when Vcc is 5.0V. This means that the input signal needs to be above 3.0V to be guaranteed to be seen as a "1". There's usually a bit of guard-band on that spec. However, I would NOT put a resistor on the iPhone output to the Arduino (RX_ARDUINO). If you did, you'd start to see bit errors at higher bit rates. At 9600 baud, you shouldn't see anything unpleasant on either side of the bus.

As he said, it didn’t do any harm to my iPod, but unfortunately I was unable to get any communication to work using this method. I tried it a few times, even with just the Play/Pause sketch, which requires no response from the iPod, without luck. It could be that I did something wrong though. The logic-level converters are under $3 so I’m okay with continuing to use them.

Back in September I had two example sketches included in the library: a Simple Remote Mode one that did play/pause, which was what I was using in my car; and a proof-of-concept sketch for Advanced Remote Mode. This went with the just-proof-of-concept Advanced Remote mode support I had implemented. Over the last few weeks I have added full support for Simple Remote Mode, which was pretty easy, and near-full support for Advanced Remote Mode (no picture block support), which was a lot more complicated. I also refactored the library code because it needed to be done, and that sort of thing makes me happy.

I have been adding example sketches as I go, and I will talk about those in follow-up articles.

iPod arduino electronics

3/2/2010 UPDATE: See update post.
4/14/2010 UPDATE: See here if you have a v1.4 PodBreakout board.

UPDATE: Better photos up on Flickr.

I've been desperately short of Arduino play time in the last few months, but I did finally find time to finish my Arduino-based iPod remote (well, version 1.0 of it anyway). My remote has a single button that toggles between Play and Pause on the iPod. I wanted one like that for my car so I could easily pause my iPod Touch without having to: find it, unlock it; find the touch-screen pause button; and finally, pause it.

So how to go about this?

Well, the iPod dock connector actually exposes a serial connection to the iPod. You can see this on the pinout, the best online version of which I found on pinouts.ru. This serial connection can be used by docks, or in my case an Arduino, to interact with the iPod. The iPod speaks AAP on its serial port: the Apple Accessory Protocol. There are several modes in AAP that you can interact with an iPod over serial in, but Simple Remote (mode 0x02) is by far the easiest, as it has no responses to deal with. Simple Remote mode allows you to play and pause the iPod, change tracks, adjust the volume and so on. Since that covered my needs it's what I implemented first. (I've also implemented part of Advanced Remote (mode 0x04) as we'll briefly see later.)

With the pinout and protocol documentation in hand I ordered a couple of cheap iPod charging cables to hack on. However, when they arrived I realized that my soldering skillz were nowhere near good enough to make the connections I was going to need. Luckily I am not the first person to have this problem, and SparkFun has the solution: the PodGizmo breakout board:



The PodGizmo has connections to all the pins on the dock connector and gives you through-holes to solder things onto: perfect!

I proceeded to hook up wires to the serial I/O pins (12 and 13), serial ground (11) and to pin 21: the rather curious-sounding "Accesory Indicator / Serial Enable" pin. The level of resistance between this pin and ground apparently tells the iPod what kind of accessory it is connected to. Since I wanted to use the serial interface, I went with a 500kOhm resistor, to select the "related to serial communication / used to enable serial communications Used in Dension Ice Link Plus car interface" mode.

With my connections made, I was about to hook it up to my Arduino, but then I remembered that the serial output of the Arduino is 5V. I wasn't sure what the iPod wanted but I guessed it probably only wanted 3.3V. I didn't know what to do, so I googled around for a bit looking at various level-shifting solutions. Some you could make from a few components but I was concerned they wouldn't be able to switch fast enough to get a good serial signal. Luckily, during my googling I came across another SparkFun gem: the BOB-08745 Logic Level Converter.



This little guy lets you talk serial (or I2C, SPI, etc) at one voltage on one side and another voltage on the other side. Again: perfect!

So with the level converter added to the mix, I was ready to hook it up to the Arduino.

Of course, hooking up wasn't going to do much without some code to talk Apple Accessory Protocol, so that was the next task. I wrote an Arduino library for the parts of the Apple Accessory Protocol that I was going to need, and a bit more besides. I posted it on github in case anyone else wanted to use it. It comes with a couple of example sketches: a play/pause one using Simple Remote mode (wonder where I got that idea from); and one for Advanced Remote mode that pulls back information for the track that the iPod is currently playing. The latter could form the basis of an Arduino-based dock that showed track information on an LCD display, for example.

Here's the example Simple Remote sketch. I'm using almost exactly this for my remote, the only difference being that I'm using an active-low on my switch with the Arduino's internal pull-up to avoid having an external resistor for the switch:



During development I used an Arduino Mega so that I could have a real serial port for the iPod and a real one for debugging messages. I probably could just have used the SoftwareSerial library with a regular Arduino for debugging, but since I had the Mega around, I used it. My library defaults to having debugging messages disabled, but you can configure it in your setup() method to route those messages to any serial port you like.

Once I had it working to my liking I transferred the sketch over to an Arduino Nano, since it would fit in an Altoids tin (of course). This is what it looked like at this point:



You can see I'm just using a simple push button for the play/pause action. The Nano is sitting on a little breadboard and you can just see the resistor I have connected to pin 21. I probably should have just put the resistor on the PodGizmo breakout board, but I didn't.

Next came testing it with my iPod Touch:



Everything checked out, so next I switched out the little button for a REALLY BIG BUTTON:



As you can see it's an Easy Button from Staples; I just took out the Easy Button's batteries, soldered wires to either side of its switch, and routed them out through the hole conveniently left by the battery lid. The Nano is sitting on an Altoids tin at this stage, but it's not yet in the tin. That came next, thanks to Mr Dremel:



I took it out to the car, hooked up the Nano's USB cable to my USB car adaptor (similar to this one on Amazon, but you can get them lots of places), and tried it out. It worked pretty well, but there was one problem: I was still using a cable to connect the headphone socket on the iPod to the line-in jack on my car. The audio wouldn't go out the headphone socket unless I plugged the dock cable in first and then the headphone cable. As you've probably realized by this point, it was completely stupid of me to still be using a headphone cable: the dock connector has connections for line out! Having caught up with my smarter readers, I took the remote into the lab at work and add hooked up the line-out cable. This gives me true line out instead of the volume-adjusted headphone output, saves wear and tear on the headphone socket on my iPod, and avoids the what-to-connect-first problem, as there's only one thing to connect.

So how does it work? It works great, thanks! The only real quirk I've noticed is that when I first connect it, my 2G iPod Touch will play audio out of its internal 'speaker' for a couple of seconds before realizing that it's connected to the dock and switching over. It even pauses the iPod when I turn off the car, presumably because the iPod sees the dock go away when the Nano loses power.

No doubt someone will point out that the Nano is a gazillion times overpowered to do a couple of serial I/O sequences, and they'd be right. But: I already had the Nano anyway; and I plan on expanding the remote soon (dash-mounted, arduinix-powered, nixie tube track status action anybody?).

iPod arduino electronics