Inside the SKYFi home stand.

[jm3000]

After seeing some recent posts that hint about the possibility of computer control of the SKYFi I decided to investigate further. I started by opening up my home stand, and seeing just what all those SKYFi pins do. The 16 pin and 2 coax docking connector from the SKYFi, connects to the circuit board via 2 coax cables, and a 14 pin connector, that carries power, audio, and data. Out of the 16 pins total only 9 are actually connected in the home stand, it appears that the different SKYFi kits use different pins (for example the car kit uses some different pins on the SKYFi connector). It seems that audio(4 wires) and power(4 wires) are passed directly to/from the SKYFi and the external connectors/ The antenna signal is split in to the 2 separate feeds to the SKYFi, see the circuit on the left side of the bottom of the board between the antenna connector and the antenna cables. More interesting are other pins, there are 3 pins that don't seem to have an obvious function, one of the pins is grounded (possibly a indicator to the SKYFi of what cradle it’s in, or what signaling to use), the other 2 pins go thru a transistor (U4), but also appear on 2 of the many empty solder pads on this board. These empty solder pads are quite interesting since they seem to be setup for a USB interface, very similar to what is used in the XMPCR. In fact it looks like this board was designed to have the exact same serial USB chip used in the XMPCR, the FTDI FT8U232AM, as U2, with most of the rest of the missing circuitry supporting this chip. One of the pins from the SKYFi is connected directly to the FTDI chip, to the serial receive input pin. The other pin from SKYFI connects to the mystery U1 IC, also conned to U1 is the transmit output of the FTDI chip. The U1 IC's purpose is still a mystery, but it may play a role in transferring control from the SKYFi's controls to the computer. Also connected to U1 is the reset line of the FTDI chip, which may indicate it has some role in resetting the USB interface as there does seem to be any thing else connected to the reset pin, and may just be there to reset the USB interface, do nothing more. Also unusual about U1, is that many of its pins are connected together, and does not appear to have a connection to Vcc. Additionally the USB subsystem is powered from the USB bus, but there does not seem to be any place for connection between the USB power and the SKYFi's power feed, so the external power supply may still be needed.

Here is the pin out I've found of the SKYFi connector on the home stand, see the attached image for the meanings of the pin numbers:

1. DC -
2. not connected (connected on Car kit)
3. Data? (RX) (not connected on Car kit)
4. Data? (TX) (not connected on Car kit)
5. Ground (Kit identifier?) (not connected on Car kit)
6. Audio Left
7. Audio Ground
8. DC +
9. DC +
10. not connected (connected on Car kit)
11. not connected (connected on Car kit)
12. not connected (connected on Car kit)
13. not connected (connected on Car kit to ground (Kit identifier?))
14. Audio Right
15. Audio Ground
16. DC -

Attached are photos of the of the home stand circuit board, I've removed the connector that connects to power/audio, etc to the SKYFi, to make the pictures clearer.

Does this mean the SKYFi was supposed to have computer control? Makes me wonder why this was left out, for technical reasons (it doesn't work right), or marketing reasons (push PCR sales, sell more subscriptions, etc)? Has any one probed these signals with the SKYFi on to see if this maybe possible or even connected serial interfaces to these lines?

[mikev]

I believe ekeefe is working on checking this out to see what happens. He's also working on an optical output mod for the SkyFi home kit as well. It would rule if the SkyFi could be computer controlled with optical output for home, then put in that SkyLink dock for head unit integration in the car.

AWESOME work is happening here...

- Mike

[nsayer]

What do you bet that U1 detects the 'power on' word coming from the serial interface and gives a special vulcan neck pinch to the SkyFi to put the CPU in the SkyFi to sleep and turn control of the 2G can over to the serial interface.

The clue to this is that the SkyLink review talked about the display going blank when control was delegated. That means that the SkyFi consists of a 2G can, just like in the XMPCR, with its serial port connected to an embedded controller that runs the keyboard and display. If you do the right thing, you can turn that embedded processor off and get control of the serial port yourself.

[nsayer]

I got a flash last night.

What if U1 is nothing more than a tri-state buffer? That is, what if its purpose in life is to detect whether or not the SkyFi's CPU is turned on or off?

What if it's just this simple: While the SkyFi is "powered off," you can use the USB connection to control the 2G can, but if you power up the SkyFi, the tri-state blocks the USB port from working? Does one of the pins on the cradle change state when you power the SkyFi on?

[nsayer]

I did some more checking and I am now 99.44% sure that TP1 and TP2 on the bottom of the board are the transmit and receive data lines as they arrive at the FTDI chip. The next step is to see what you have to do to get the data to arrive there. If the parent post is right, then I'll need to either populate U1 or bridge two of the pins together.

I've not had really good luck figuring out what U1 is supposed to be.

*BONUS* I've discovered that TP4 and TP5 are the serial data pins coming from the SkyFi connector! TP3 appears to be grounded.

[nsayer]

Some aspect of this must be eluding me. I've got a Bluetooth-to-serial adapter hooked up to a little home-made MAX232 based RS-232 to TTL adapter. If I loopback on the TTL side, I can see that the circuit is working.

Over on the SkyFi side, I've taken apart the home cradle and wound up lifting the PCB trace from under TP4. Whoops. So instead, I stripped the wires going to the connector and brought them down to the TTL side of the MAX232. No joy.

There must be something else going on that somehow gets the SkyFi to go into "serial control" mode. If anyone has any idea what, please let the world know!

[jm3000]

Have you tried doing the 6-0-2-XM (with the SJYFi off) combination, to put the SKIFi in "PC Connection" Mode, and then taking to it?

I'm guesing you hooked into the data lines and you not seeing any thing from the SKYFi, even with the SKYFi on in it's normal mode? Those Tx/rx line from skyfi also go thru U4 on the home kit board, which if you've removed the cables from the home kit board, they will no longer be conncted to it.

This is very intresting work, I'd love to be able to get the PCR functionality with the SKYFi.

[nsayer]

That almost did it. MacXM is now capable of controlling the SkyFi just as if it was a PCR. The only problem is that there is no audio. I know the audio is hooked up correctly, because if I just turn the SkyFi on, I hear it. So this PC Connection mode is doing something different we still have to figure out.

[jm3000]

There are a couple of post's here, such as this one, that mention something called SKYFi mode, on the PCR. Unfortunately it's not clear what this is referring to, maybe the official pcr software has a mode for interfacing with the SKYFi, perhaps with some additional initialization.

[nsayer]

There's nothing in the spec that talks about anything like that. I also tried fiddling the buttons while it was in PC Control mode and that didn't help.

There must be some other key combination that puts it in PC Connection mode, but with audio.

I'm begining to think that the SkyLink probably has an IR LED inside of it and it sends the correct code, not unlike the thing they sell in the store that powers your SkyFi up when you turn on the ignition.

[nsayer]

If you can't tell, this is driving me insane.

I went over the unused pins with a voltmeter. Pin 2 goes from 0 to about 3.3 volts when you power the SkyFi on, either normally or into PC Connection mode. Pin 13 always appears to have 3.3 volts on it. The other unused pins show 0.

Alas, I don't have the stones to take my Boombox apart. I wonder if pins 10-12 have something to do with the boombox volume control.

I still have no clue why there's no audio.

[powerondude]

I thought I remember reading somewhere that there are pins on the cradle(s) that identify what type of cradle the unit is currently docked to. Could it be that a combination of those tell the skyfi to go into "PC" mode?

[tps]

What looks very interesting to me is the RF spliiter section. From the pictures, it looks pretty darn symetrical. I wonder if you coud use the splitter from a Skyfi cradle to drive 2 XM receivers from a single antenna? An even better question: would the forthcoming stand-alone splitter drive 2 receivers from a single antenna?

It would be an interesting experiment to get one of the splitters (either XM or Sirius) and see if I could get it to drive my XM and Sirius receivers from a single antenna.