09.15.10
iPhone hands-free using Line In-Out, or not.
So here’s the goal. I want to plug my iPhone into a dock and use my audio kit as a hands free kit for making and recieving calls. (In case you don’t know everything I have in the office which makes a noise or needs a microphone is routed through a set of mixers and processors and I can records from any source for podcasts etc etc. geeky but cool – if you’re me)
As you can see from the pinout below, the IPOD connector on the iPhone supports line-in and line out although you do need to put a specific value of resistor across a couple of lines to ‘switch’ this functionality on.
| Pin | Signal | Description |
| 1 | GND | Ground (-), internally connected with Pin 2 on iPod motherboard |
| 2 | GND | Audio & Video ground (-), internally connected with Pin 1 on iPod motherboard |
| 3 | Right | Line Out – R (+) (Audio output, right channel) |
| 4 | Left | Line Out – L(+) (Audio output, left channel) |
| 5 | Right In | Line In – R (+) |
| 6 | Left In | Line In – L (+) |
| 8 | Video Out | Composite video output (only when slideshow active on iPod Photo) |
| 9 | S-Video Chrominance output | for iPod Color, Photo only |
| 10 | S-Video Luminance output | for iPod Color, Photo only |
| 11 | GND | If connected to GND the iPhone sends audio signals through pin 3-4, otherwise it uses onboard speaker. |
| 12 | Tx | ipod sending line, Serial TxD |
| 13 | Rx | ipod receiving line, Serial RxD |
| 14 | RSVD | Reserved |
| 15 | GND | Ground (-), internally connected with pin 16 on iPod motherboard |
| 16 | GND | USB GND (-), internally connected with pin 15 on iPod motherboard |
| 17 | RSVD | Reserved |
| 18 | 3.3V | 3.3V Power (+) Stepped up to provide +5 VDC to USB on iPod Camera Connector. If iPod is put to sleep while Camera Connector is present, +5 VDC at this pin slowly drains back to 0 VDC. |
| 19,20 | +12V | Firewire Power 12 VDC (+) |
| 21 | Accessory Indicator/Serial enable |
Different resistances indicate accessory type: 1kOhm – iPod docking station, beeps when connected 10kOhm – Takes some iPods into photo import mode 68kOhm – makes iPhone 3g send audio through line-out without any messages 500kOhm – related to serial communication / used to enable serial communications Used in Dension Ice Link Plus car interface 1MOhm – Belkin auto adaptor, iPod shuts down automatically when power disconnected Connecting pin 21 to ground with a 1MOhm resistor does stop the ipod when power (i.e. Firewire-12V) is cut. Looks to be that when this pin is grounded it closes a switch so that on loss of power the Ipod shuts off. Dock has the same Resistor. |
| 22 | TPA (-) | FireWire Data TPA (-) |
| 23 | 5 VDC (+) | USB Power 5 VDC (+) |
| 24 | TPA (+) | FireWire Data TPA (+) |
| 25 | Data (-) | USB Data (-) |
| 26 | TPB (-) | FireWire Data TPB (-) |
| 27 | Data (+) |
USB Data (+) Pins 25 and 27 may be used in different manner. To force the iPod 5G to charge in any case, when USB Power 5 VDC (pin 23) is fed, 25 must be connected to 5V through a 10kOhm resistor, and 27 must be connected to the Ground (for example: pin 1) with a 10kOhm resistor. iPod 5G can also be forced to charge by attaching the data + and the data – pins to the 5v via a 10k Ohm resistor ( BOTH PINS) and connecting pin 16 to the 5v (ground). (Confirmed working with iPod 5G 20GB) To charge an iPhone 3G / iPod Touch 2nd gen or Ipod Classic (6th Gen), usb data- (25) should be at 2.8v, usb data+(27) should be at 2.0v. This can be done with a few simple resistors: 33k to +5v (23) and 22k to gnd(16) to obtain 2v and 33k to +5v and 47k to gnd to obtain 2.8v. This is a notification to the iphone that it is connected to the external charger and may drain amps from the usb. It’s also possible to charge the iPod’s or iPhone’s battery to make use the of internal +3.3v output (18) terminal to connect the USB Data + (27) thru a 47k ohms resistor and the USB Data- (25) thru a 47k resistor to the USB Power source +5v (23). This way the USB function is still useable for normal operations and makes it easier the fit in a plug. The resistors are not to critical 2x 150k’s still work. |
| 28 | TPB (+) | FireWire Data TPB (+) |
| 29,30 | GND | FireWire Ground (-) |
Back side of dock connector; 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
My simple brain therefore led me to believe that is should be a simple matter of using those lines and feeding them at the correct level from the in/out of my main mixer. HAH!
The Line-Out is indeed enabled BUT the audio from phone calls is not presented on that circuit. I'm sure that this is a software thing but for the life of me I can't understand why it wouldn't be enabled in this way unless it's a simple method of controlling the ability for 3rd parties to create hand's free kits. It's bluetooth or nowt!
I did get a universal dock of eBay and I am feeding the line out from it into my mixer just in case I ever need an additional audio source but I'm disappointed that I can't use it for calls. The only way I can achieve what I want is to use the top connector on the iPhone which is a TRRS connector however this is set up to support headphones and an electret mic so I'm going to have to mess around with capacitors and resistors again, BAH!
iPhone TRRS connector
Tip - Left Audio
Ring - Rign Audio
Ring - Ground (I know!)
Shield - Mic in
I did find an interesting article by a guy who'd created a neat little box to use to record his calls, but this still relied on using 'standard' headphones and an electret mic so doesn't really help too much. Oh well, where's my soldering iron?!
