connections?

[rcpilot]

Hi I found this schemeatic for an audio operated switch but it was for 1 relay so i added another to be able to do what i wanted

switcher.jpg (114.06 KiB) Viewed 13025 times

, the audio input on the left of the diagram comes from the line out of a sat nav device ( mono but that has 2 connections one of which is the ground ) so I am sumising that the ground goes down to the negative rail on the switching device?
K1 and K2 are the relays, J1 and J2 are jack sockets, J1 is connected to the output of an Mp3 player, J2 is connected to the aux stereo input socket of the car stereo unit, in the unswitched mode (as per dia) the mp3 player goes straight to the aux stereo input via J2. In the switched mode the audio input from the sat nav is fed to J2, J1 is disconnected.
What I want to know is as a stereo line has R, L, and ground and all the power supplies, ie mp3 player, sat nav, and the switching device come from the cars battery (which will be regulated down to 5 volts) can all the ground connections of the stereo and mono lines be connected to the negative rail if not then obviously the ground connections on J1 and J2 will have to be maintained and not connected to the negative rail, but what about the audio from the sat nav, the ground from that is already connected to the negative rail in the switcher and only the + connection (so to speak) is connected to J2 so when in the switched mode how will the audio from the sat nav be able to go through J1 to the aux input of the cars stereo unit with only 1 connection?

[piratepaul]

Hi, this does not make sense to me.
I should think everything should be connected to ground, I have used 5v power supplies and 12v from the car on the same board there, is one in the car now.
I will have a think about it, I am unsure of the layout of the relays ( the diagram is unclear ), I think it could be improved.
The audio switch is ace, there was another guy looking for one of those ace ace ace.

Tar&stuff.

[Pauldf]

I think all the 555 chip is doing is a 1 shot, when it is activated by Q1 it will turn on the output pin 3 for a determined period. I don't know if the 555 has enough power to drive two relays tho, you may need to place a power transistor in there.
As for the audio inputs you can't really join L and R together as it will mess with the audio, for switching purposes you can just use mono from the sat nav i.e. use the right channel only.
What are you wanting it to do? I'm guessing you are wanting it to operate relays silencing the mp3 when the sat nav talks?

[rcpilot]

That's correct silence the mp3 when the sat nav talks, the 555 can be set via the variable resistor for up to 5 secs, i thought that if i set it for about 2 secs if the sat nav talks for longer than that the timer will be reactivated.
The relays are stated as 4.5 volts for the coil, if the timer 555 does not provide enough power to activate the relays where would i put the power transistor.
I cannot see how joining the L and R together in K2 would matter as the souce is mono and when the relays are activated the stereo in K1 is disconnected so K2 would only be supplying a mono signal to both the L and R inputs of the car stereo, don't know?

[Pauldf]

If it is mono then I'd just use one side. I take it the sat nav goes in on the "audio input", the mp3 to j1 and stereo output to j2?
Personally I'd try to get it working with an LED off pin 3 as a test, just to see if I could get it working so when an audio input is detected the LED comes on for a few seconds.

When connecting the relays a transistor will just need to go, along with a resistor between pin 3 and the relay. Something like a bog standard BFY51 will probably do.
Lose the reverse biased diode on pin 3 and put it across the relay coils instead.

[piratepaul]

I would have thought the 555 is triggered by the sound signal from the sat nav, the 555 re_triggers with every sound pulse.

MP3 and aux/input should be earthed which leaves 2 wires one from satnav and one from MP3...MP3 must switch off when satnav is on and vise versa.
Some sort of switching logic needed between 555 and relays or transistors instead of relays.


I will av a fink about it.

Tar&stuff.

[piratepaul]

Hi, it is quite difficult to scroll around on the diagram, remember it then write.

I cannot understand the diagram, it is unclear how many wires are involved.

How many wires from the satnav?
How many from the mp3 and how many to the stereo input?

There should be 3 wires or 2 wires and earth for 2 channels I would have thought.

So this is one normally on and a normally off relay is it?
I think the jacks are wrong or I have not got my head around it.
There should be 2 jacks 2wires each or one jack 3 wires.

A D latch might be a more robust way of switching the relays if they are both normally off...less power drawn from the 555.

Tar&stuff.

[rcpilot]

Hi all Thanks for the replies, sorry for not answering sooner but been away for a week.
Right there are 2 wires from the sat nav 1signal and 1 ground
there are 3 wires from the mp3 player 1 left, 1 right and 1 ground
the relays as in the diagram are both in the non activated state, so would both draw power from the 555 when activated.
what i could do is, as the signal that comes from the sat nav is just mono, I could just use one side of the DPDT relay K2 to feed the aux input and the other side to control the other DPDT relay K1 and not use the 555 .
That way the 555 would only provide power for K1, and K2 would get it's power from rail voltage controlled by K1, a rehash of the wiring would obviously need doing

[piratepaul]

How about a revised diagram, I can't make that out.
What you are saying in the last post makes sense but, you may need to be sure that the MP3 is off when the sat nav kicks in and as the relays have switching delay time there may be a few Kseconds or so when both relays are on.
Might be OK but might fry the MP3, a delay such as another 555 in monostable mode would sort it,

Tar&stuff.

[rcpilot]

Hi here is a revised diagram of the relays, obviously they are in the normally open state.

File0001.jpg (45.19 KiB) Viewed 12977 times

in this state the mp3 player is playing into the cars aux input connection through K1 and through J2.
When the sat nav chirps in K2 goes into the closed state and feeds 5 volts to K1 thus disconnecting the mp3 from J2 but also feeds the sat nav audio at the same time to J2 but only using the left channel.
I cannot see how this setup could fry the mp3 player as all the relays are doing is redirecting an audio signal,( apart from supplying K1 with 5 volts). Don't know could be wrong.
When the timer drops out K2 disconnects the sat nav audio from J2 and simultaniously disconnects K1 from the 5 volt supply rail thus reconnecting the mp3 player to the cars aux input connection and is in a state of readiness for another direction from the sat nav.