Mobile psu 4 hp 2000

I have built a 14.5V to 19V inverter for my HP laptop and I have the cord for it, but I can't find the exact information about how to hook it up. The inverter plugs in to a cigarette lighter of my off road vehicle and I used a Linear Technology LT1270A 10A High Efficiency Switching Regulator to boost the voltage.
I have a HP 2000-2a00 laptop with the 3 pin plug. The outer ring is negative, the inner ring is positive, and the center pin is referred to as the ID pin. Suggestion on google are to use resistor from positive to the ID pin ranging 1K to 430K and one suggestion for a 20K in series with a 100nf. Another suggestion is that the psu and computer 'communicate' via the ID pin, smart power supply.
If any one can elaborate on the smart power supply, It would be interesting, but what I need most, is what to put between the positive and the ID pin.
Thanks,
Kinarfi, AKA Jeff

Sorry cant help you much with your issue, but I might be making one of those, I've needed 12v to 19v for laptops a couple of times and just bought one for 35 quid.
If you have the original mains psu cant you scope the centre pin and see what goes on?, I couldnt see whay they'd bother having just a resistor connected, you could easily detect a supply connected without the need for that, a data line would make more sense, maybe connecting a resistor is an option for 'dumb' supplies so it might still work.

I know on certain PSUs (Dell I think) they have a 1 wire communication device from Dallas Semiconductors to identify the type and rating of the PSU - haven't got a clue on the HP stuff though.

I used the cord that bigal_scorpio sent to me and plugged it into my computer and scoped the ID lead to ground and it has a 20Hz square wave on it with an on time of about 10% and an amplitude in the millivolt range. That was with no loads on the any of the leads, I haven't figured out how to open the circuit up so I have access to get any measurements while in service.

Good news, I let the computer battery run down to about 45% and then plugged the cord in from my 12 to 19V inverter, when the battery was fully charged and the cord plugged in the power supply pulled 1 amp, after letting the battery run down and plugging the cord back in, it pulled 4 amps and charged the battery back up, I did scope the resistor and it had a voltage of about 1.2v dc and an ac wave form of a + spike and then a lesser - spike at a freq of 65 khz, there were a few more details, but I left the info down stairs. The resistor I use is a 1/4 W 220K 5% .