I have an f700bt and the startup time (45-60 secs) is annoying... especially if you just turn off the car for 5-10 mins.
I also have an u310bt, which they seemed to have solved this problem by using a separate PNA faceplace (much like other portable gps devices) which has a battery in it and can go into lower power standby mode.
Thanks to this thread I have been reading through the PAC TR-7 manual, and for 15 bucks shipped on ebay, i dont think you can beat the various functionality of the thing.
Looks like i want to use mode #12 - "3 programmable timer outputs on constant trigger"
However, the max delay time indicated above was less than 5 mins. This seems just a bit short for me.. I would think my sweet spot would be between 10-15 mins of delay-to-off.
I also saw this relay-delay-turn-off design while googling: http://www.astron.nl...v/poweroff.html
I like this guys idea, mainly because it could preset to do a longer, say ~10 mins, delay, but is fixed and can slightly vary since the timing is based upon the capacitor drain characteristics. Anyhow, any value between 10-15 mins seems like it would do.
Since we only need to power the acc (red) line and not the battery (yellow) line, and my understanding is the main current draw is off the battery (yellow), I was thinking about simplifying his design a bit to eliminate the relay, and go straight to using the mosfet for the switching task on radio acc line. (also note his corrections on his site about wiring of mosfet leads and the resistor values for the manual-off switch..

I see that the B+ (battery, yellow) line on the avics is rated at about 10A, and this must be the main load carrying line. However, I'm wondering if anybody has done real world current measurement test on ACC+ (acc/ign, red) line to see how much draw i will need to handle with the mosfet?
On the other hand, the PAC TR-7 looks nice:
I see that the TR-7 can power up to 2A @ 12vdc. I would hope acc line doesnt draw more than a few hundred mA max!
I'm also thinking about the fact that when acc power goes off, I want to delay the turn-off of the unit, but I may want to mute the unit. So I'm reading over the instructions and wondering if somehow we can use the delays on this...