Electronics 2000

Magic, I can understand it now.
Where you have +5V to K2, should come from pin 3, of a second 555, capacitor,variable resistor, circuit.... The same as above but without the transistors, triggered from pin 2 of the first 555.
This second circuit switches the mp3 back on after the sat nav has switched off and not before. Otherwise the mp3 and satnav will have a chance to be on at the same time, which maybe OK but then again might fry satnav or mp3.
There is likely to be trouble at switch on than at switch off because of switch bounce in the relays.

Tar&stuff.

I think you will need a third 555, the 555 they you have switches K1 off, and switches the new 555 for about 50/100 Is which switches K2 on, this means you miss a split second of sat nav info, but I should think that would make no difference.
The second 555 in the last post can be switched bk either 555 number 1 ( the one you have) or number 3 the one in this post.
Unless any one can think of a better circuit or you want to risk it?

It looks great what you have said and drawn there if you want to risk it.
It does not say where +5V to K2 comes from. A case of will the 555 handle the current for 1 or more relays?

Tar&stuff.

Actually that should be mS not Ks sorry.

It didn't even say Ks the baly predictive text changed it to Is and I never noticed.
(Did you hear about the lad in america who made a clock and got arrested on terrorist charges, done it now expect the Feds, keep you hands on the dashboard ...freeze etc.)

It just struck me.

A suppressor cap across each relay to take out switch interference maybe try with out maybe first not sure what size caps.

Tar&stuff.

So basically the relays have got to work so that they first disconnect the mp3 player before they connect the sat nav and then in reverse to switch the mp3 player back on.
Obviously the sat nav signal is what triggers the relays and then that same sat nav signal is what goes out to the aux input of the car.
I will have a look at the wiring again and see if I can rehash it so that it does exactly as above.
A question say on a DPST relay (for simplicity sake) is it possible for all 3 conntacts to be connected at the same time, if not then a rehash of the wiring might get around the problem of both the sat nav and the mp3 player being on at the same time.

I am not sure what you mean, about all 3 connections on the relay, do yo mean relays?

It might be OK as it is, perhaps a crakle on switching hence a cap or caps across the relay, relays.
The relays will open faster than they will close, there will be switch bounce on close but not on open...how expensive is the equipment? I should think it would probably maybe if your lucky be OK ...but... It might damage sat nav or MP3.

Tar&stuff.

But yes that's what I mean.

Tar&stuff.

Hi what I meant by "can all the 3 contacts be connected at the same time" was if 1 relay was just used and on switch over could it be possible for all the contacts to be momentarily connected together either at activation or deactivation, if not then 1 relay can be utilised instead of 2, just needs rewiring if this is ok and no possible damage to either sat nav or mp3 player then I will try it.
The sat nav does not have a line out so i am going to have to use the speaker wires and wire them to a converter (which I have ) so the high level speaker output will be turned into a low level line out.

Also in the last dia I intend to feed the mono sat nav signal to both L and R hand channels of the aux input of the cars stereo so that the instructions come out of all the speakers in the car. I can put up with loosing a fraction of the sat nav's instructions as it just about always say's the instructions twice

That would solve the problem.

Tar&stuff.