Circuit logic and LED indicators

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MikeT
Posts: 4838
Joined: 11 Jun 2007, 16:17
x 187

Circuit logic and LED indicators

Post by MikeT »

I have a circuit that is switched at both ends - i.e One on the positive side and one on the negative side. Is it possible (I'm sure it is but I can't get my head roud it) to have one LED show when the positive switch is on but the negative switch off and then a second LED to show when both are on?

OwenP
Posts: 308
Joined: 31 Jul 2004, 19:05

Post by OwenP »

I'm pretty sure it is possible, but it has been a long time since I did any electronics.

You should be able to wire an LED across each switch indepdantly so that they will show when that particular switch is closed. For the negative this should be a case of wire the LED in parrallel to what the switch is controlling someting like this:

+ _____/ _______ GRD
...................|
...................LED_____GRD

For the positive switch however you may need to be a bit more clever, the simplest solution which comes to mind would be a double pole single throw switch, where one pole control the circuit you have the two switches on and the second is an indepent circuit just for the indication LED. Will try to draw you a schematic when I finish work, haven't quite got time in my lunch break.

OwenP
Posts: 308
Joined: 31 Jul 2004, 19:05

Post by OwenP »

As promised a rough circuit diagram, unfortunately I only have paint available at the moment so it is a bit crude.

Image

Point A is the Double pole single throw switch I mentioned, (your +ve side switch) basically this allow one switch to control two circuits, I drawn it with a common +ve feed but the second circuit can be totally separate in everything bar the switch.

Point B is then your second switch (the -ve side) wired as I said in the last post.

Hope this helps.

Think I might to go and find a proper electronic diagramming tool though.

MikeT
Posts: 4838
Joined: 11 Jun 2007, 16:17
x 187

Post by MikeT »

Cheers Owen, I knew it'd be a simple deal, just not simple enough for me to imagine :oops:

In my diagram I put the second LED on the wrong side of the negative switch and didn't realise that would complete the circuit on both LEDS even with both switches off! :oops:

I was going to prototype and test my circuit but I think I'll skip that idea and use yours instead :lol: