Multi inputs to one light with no return

[stuee]

Hi.
Basically to explain the title.
I have a boat im rewiring, i have light on the gauges which i dont have a switch for them.

I have 3 different light circuits switched and also the motor ignition key all 12v.
I dont want the gauges on all the time only when items are in use.

What i was thinking if it works would be




Gauges
|
| | |
diode diode diode
| | |
nav light floor light key ignition


would the diode stop the back flow of the 12v so basically if i turn on the nav light it wont put 12v through the floor light or key ig but light the gauges.


As i said its low ampage and 12v battery.

thanks

 

[Nigel Goodwin]

Yes, it's called a diode OR gate.

 

[stuee]

Thanks Nigel.
I have been looking as some doiode or gates and they all seem to have a resistor. do i need this and how would i work out what value.
Also with the diodes do i just get the ones rated higher than the ampage (not more than 1a)

cheers

 

[dr pepper]

You dont need a resistor, I think the ones you've seen are for something else, maybe an led.

1n5404's would be good enough for 12v 1.2w, the are actually well oversize, the leads on them are convenient for crimp terms.

You can get diode matrix's from some chandlers, it would however be a whole lot cheaper just making one up for your application, screw 2 lengths of screw term block to some hardboard then fit the diodes inbetween them, you then have a safe platform you can secure, if you like you could hot glue them down too to protect from vibration.

You only need to light up relevent guages, ie if the engine isnt running you'd only need the voltmeter and water tank meter to light up, oil pressure/fuel etc isnt needed.