01.04.11

iPhone integration with audio kit – the solution

Posted in Home at 12:01 pm by admin

A little while ago I set out on a quest to be able to insert my iPhone into my audio setup to allow me to use the studio as a hends free interface for calls. It’s seems very frivilus now that I read that back, but it’s actually important to be able to caprute the calls to.. so there!

Anyway, time moved on and I had some little success building various cables and experimenting but my solution came in the form of a relatively simple little device designed to do something totally different (isn’t that always the way), namely to provide an interface to connect an electric guitar to the iPhone (or iPod Touch or iPad). The manufacturer is Peavey – those of you in the know will already have the association made as Peavey are well know for their guitar amplifiers among other things – and the device is the Ampkit Link.

This innocuous little white widget does exactly what I want it to do and I’m now a very happy, and very audio integrated, person. The XBox side of the equation is going to be handled by a simple adaptor cable which I’ll build up as the connections are different on the iPone jack – and therefore on the Peavey device – than on the XBox controller.

As an aside, the app which supports the Link hardware is free for a basic version and, if you’re a guitar person with an i-Device, might be worth a look-see.

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09.15.10

iPhone hands-free using Line In-Out, or not.

Posted in Home at 12:09 pm by JohnB

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!

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?!

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09.12.10

XBox Live to Line inputs and outputs

Posted in Gaming, Home at 12:14 pm by JohnB

One of the projects I’ve got bubbling is the connection of XBox Live communications to my audio set up.

The typical way of using XBox Live comms is through a headset connected to the controller. This means that there’s a microphone input to the controller and a mono output to the headset via the 2.5mm jack plug. The plug is a standard TRS (Tip, Ring, Shield) and must therefore share a common ground between the mic input and headphone output, the layout is thus:

The Tip carried the +’ve for the mic, the Ring carries the +’ve for the headphones and the Shield carries the common ground signal for both.

So the cabling isn’t that complicated, however the signal I want to feed to the controller is not at mic level, it’s going to be line level as it’s an AUX-out from my main mixer so we need to do something to attenuate that signal back. There’s also the issue that the controller is expecting to have an electret-type microphone attached and as a result supplies a voltage in order to power the mic, having this up to the line output on the mixer isn’t going to do a lot for the signal quality!

The solution for both of these issues is the following:

                 C1
+Line level in --||----R1----+-- +Mic level output
                   +         |
                             |
                  +----R2----+
                  |
Ground (input)----+--------------- Ground (output)

R1 = 10 kohm
R2 = 1 kohm
C1 = 10 uF

In practice I actually used 2 x 10K resistors in place of R1 as the levels being supplied on the Aux Out of the are still a little higher that the contoller and the audio ‘gubbins’ doing the encoding are expecting so I was getting a lot of distortion and noise – this probably gives some indication of the overall quality (or lack thereof) of the components used in the standard headset, but that’s another issue!

I tested the various configurations using the XBox Live messaging system by attaching a voice message and using the play-back to listen and set the output levels. All working very nicely!

Then I hit a wall. The ‘output’ side of the XBox Live Audio was planned to be routed into an input channel on on of the tertiary mixers – the one I have dedicated to the games consoles – and I felt confident that this would be a pretty easy task, the mixer was happy to take an unbalanced input and the cable was a simple connection to a mono 1/4 inch jack. The reality is that when I plug in the jack to the mixer by mic levels get sunk. There’s simply nothing there, in fact the XBox reports there being no connection in place. So I’m stuck!

My workaround has been to make a simple cable to carry just the mic signals so I can use my boom mic and i’ve told the XBox to send the Live output to the main speakers, it works.. but dammit it’s not right! I need to look at what’s going on, but that’s where we are now.

I’ve alos started looking at the connection of my iPhone to the audio kit for hands free calling and I’ll update that this coming week.. things are never as easy as they should be!

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