Re: Request for circuit to supply power:
I had good luck just using a couple of resistors to drop 3V from a pair of batteries to 2.75V. I used a 400 ohm and 2.7K ohm resistor in series across the batteries, drawing power off of the 2.7K ohm resistor. There’s a photo of the circuit in an earlier post.
The problem here seems to be a change in the power available from Apple’s headphone jack, not any deficiency in the HiJack device itself. The older iPhones simply supply more power. With the iPhone 4s and all of the iPads I’ve tried, you need an external power supply.
It seems to me that a power supply based on a coin cell battery should be easy enough to build, too. This would easily fit on the small daughter board that plugs directly into the HiJack board, maintaining the small size. I’m going to order some parts and build one, but if anyone beats me to it, be sure and post the results.