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I'm currently attempting to add an iPhone Dock to my old Aiwa Hi-Fi system. I've used a multimeter and established that the VCC for the Hi-Fi's internal circuitry is 4.83V.

I've used information from Pinouts.ru to come to the conclusion that the pin connections should be:

  • 1: GND
  • 3: R-out
  • 4: L-out
  • 11: GND
  • 15: GND
  • 21: 1K ohm - GND
  • 23: VCC
  • 25: 2.8V
  • 27: 2V

So firstly, have I understood the resource correctly, and is it okay to float the unconnected pins?

Secondly, I'm going to get the 2.8V and the 2V using potential divider circuits from VCC to GND. Are these resistor values appropriate?

2.8V: R1 = 43K | R2 = 56K

2V: R1 = 56K | R2 = 43K

Oh, and one final thing I would like to ask, and this may seem really simple but I should probably check! If there is a connection on the PCB labelled AGND, can I use that as GND?

Adi Bradfield
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    "Secondly, I'm going to get the 2.8V and the 2V using potential divider circuits from VCC to GND." That... sounds like an awful idea. Plus, are you sure these don't come from the iPod instead of the dock? – Ignacio Vazquez-Abrams Aug 29 '13 at 19:05
  • @IgnacioVazquez-Abrams Sorry, I only have limited knowledge of electronics! Can you explain why that's such a bad idea? And from the resource "To charge an iPhone, 3G, 3GS, 4 / iPod Touch, 2nd gen, 3rd, 4th or Ipod Classic (6th Gen), usb data- (25) should be at 2.8v, usb data+(27) should be at 2.0v. "....." This is a notification to the iphone that it is connected to the external charger and may drain amps from the usb." So I'm fairly certain it comes from the dock? – Adi Bradfield Aug 29 '13 at 19:07
  • If they were actually supplies (either to the iPod or to an external device) then more power could be drawn from them than the resistors would allow. But since it's just a notification then disregard what I said. – Ignacio Vazquez-Abrams Aug 29 '13 at 19:11
  • @IgnacioVazquez-Abrams Pins 25 and 27 are USB Data + and -. Only used for signaling, not power draw. – Passerby Aug 29 '13 at 22:39
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    This question IS ON TOPIC. ""consumer electronics such as media players, cell phones or smart phones, except when designing these products or modifying their electronics for other uses"" Hacking in an ipod dock to the internal power of a HIFI is modifying it for other uses. – Passerby Aug 29 '13 at 22:57

1 Answers1

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This is essentially correct. Two things though.

One, you should make sure the vcc you are tapping, which you said is ~4.83v, is regulated.

Two, you should make sure that you have enough headroom to actually use that 4.83v line. The 2.8v/2.0v signaling indicates to the iPod that it can draw up to 1 AMP of current. That may be more than the hifi can spare or is designed for, on top of what it already pulls. You might need a bigger power supply, a better regulator, or add a heatsink/cooling on the existing one. If it regulates down from a higher voltage, say 9v or 12v, you could add a second regulator just for the iPod and replace the power supply (Assuming it is an external ac to dc power adaptor. If it is an internal one, way more complicated).

Even the 500mA charging mode might be too much. Just a heads up.

Also, pin 21, you could connect a 1k resistor to ground for Dock mode, but sometimes if the dock has no controls, you really can't use it for anything. An alternative is using a 66k resistor to ground. This puts it in line-out mode, where it uses the dock connecter for audio instead of the headphone connector. You could test both before finishing to see which one you prefer.

Passerby
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