Custom 12v Electronic sleep timer circuit needed for Headrest DVDs

[danieljsinclair]

I have some headrest DVD players that the kids love. I was able to wire them through my existing AV pack (I an E39 with the have the Mk4 Nav + TV option). The trouble is, they'll only work when the ignition is in position 1, because that's the way I've wired them. Obviously I don't want them left on when I exit the car (usually).

So that's the trouble, sometimes, when the kids (between 2 and 4 years old) are watching a movie I'd like to keep it running when I pop out of the car for a couple of minutes. For instance, when paying for petrol. Obviously I don't want to leave the keys in the ignition, and I normally lock the car for the 3-4 minutes it takes to go pay.

What I'd like is a simple time circuit that can keep power to the headrest DVDs for a short period, say 5 to 10 minutes. Think of it a little like the BMW 'sleep mode'.

I have key-1 power and also permanent power in the center console where they're wired. I'm guessing what I need is some kind of transistor, capacitor, 555 circuit kind of thing where the circuit takes power from the permanent feed as long as the Key-1 power feed is live. But as soon as the Key1 power is removed it will keep drawing power from the permanent feed for a few more minutes. Preferably tunable to between 5 and 10 minutes.

Ideally, a pushbutton or switch that disables the circuit or simply shorts the timer to zero would also be useful if I'm home and leaving the car completely.

Well that's the limit of my not quite passable O-Level electronics grade knowledge exhausted. I believe I could solder one together from components if I knew what to build but other than that I don't really know where to start.

Is there anyone in this forum with enough electronics knowledge to ***-packet sketch a workable circuit for me that would do this?

many thanks