Stand alone PB controller

[ejbommer]

Has any one tried to create a stand alone unit to control a PB.  I am interested in building an interface that allow me to mimic my Passat Monsoon head unit then install audio out RCA’s so I can hook the unit up to any audio device and control it with a simple key pad.

I have been monitoring the data bus and have written software to convert the data in a hex format.  I think I am getting close but would like to look at another design to confirm my thoughts and see any lessons learned.  I have seen a few designs that mimic the PB data out to the radio but, none going the other direction.

I am also having issues trying to measure data, when the data out from the PB starts.  It’s driving my entire signal negative (Clock in and Data in) during its transmission.  I am sure it’s a grounding issue.  I am using pin 3 as my scope ground.  Thinking about running a wire directly to the negative post on the battery and measuring any delta’s and noise between the grounds.

[S80_UK]

I am using pin 3 as my scope ground.  Thinking about running a wire directly to the negative post on the battery and measuring any delta’s and noise between the grounds.

You mean pin 3 on the 26 way connector on the Phatbox???  That is an audio ground - depending on the box it may not be directly coupled to the signal ground for the control signals - that is pins 4 and 16 which are also the power ground.

You will see slight negative excursions on signals due to ground jumps as the Phatbox and hard disk power up, but nothing in the volts range - maybe 100 milli-volts or so.

Be very careful where you ground the scope - and I would be inclined to avoid adding extra ground wires.  Get it wrong and things may go bang.  As an alternative you could ground the scope to the chassis (battery negative) and then look at everying relative to that.

CD changer protocols vary a lot.  I assume you have already searched for any info related to the protocol used by your head unit on the web?  Another option if you just want to control the Phatbox and not worry about compatibility would be to load up an alternative firmware into the Phatbox.  I don't have details, but I have read that the TrafficPro format is relatively straightforward, and there is Phatbox firmware for it.

Good luck !

[ejbommer]

I am using pin3 on the 12 way which is supposed to be pin 4 and 16.

The voltage drop I am seeing is 4 volts, I agree if was due to the internal workings I would see in the 100 mV range.

Thanks for the tip about the traffic pro.  I will reaserch it and see if there is any good stuff on its protocol.

[S80_UK]

I am using pin3 on the 12 way which is supposed to be pin 4 and 16.

The voltage drop I am seeing is 4 volts, I agree if was due to the internal workings I would see in the 100 mV range.

Have you traced the pin you are using to the PB connector?  Looking at the pinning diagrams on http://www.phathack.com/index.cgi?page=pinouts, if the pin numbering pattern was reversed then the pin you are on may be a control signal.  If that went high, then other signals that are already low could appear to go negative by about 4 volts or so.