How to turn off a LED with 3.7v

[NickDB]

How can i make a LED turn off with 3.7v? Very limited on space.. A 1.2v LED is always on, how can i make it turn off when a switch is pressed giving 3.7v to another component?
My understanding of electronics is limited.. Im hoping for a magical combination of components to be the answer!

 

[Bluejets]

Show your circuit diagram.

 

[Harald Kapp]

A relay or transistor can be used. Look up this ressource.

 

[NickDB]

Hi,
I looked at the page but i fear my knowledge is too limited to understand it..
I drew this diagram. The R is a resistor for the LED, the circle on the right is the 3.7v component.. I need the led to turn off only when that component is on/ when the momentary switch is pressed

 

[Harald Kapp]

Please upload the schematic (PDF, JPG...).
The link you provide is inaccessible from my computer.

 

[NickDB]

Diagram

 

[Martaine2005]

Hi Nick,
I think you need to "think outside" the box with this!.
Hmm, I wonder what would happen if you put the LED directly across the switch?
What do you think Harold?

Martin

 

[Javier Manzano]

I don't really know if this is the kind of circuit you want...

In any case, as far as I can see, the LED would turn on depending on the value of the resistor AND how you place it (cathode/anode). I don't understand the question or if this is even the circuit you're trying to draw though

 

[NickDB]

hi javier,
If you look at my diagram, the led will always be on.. How can i make it turn off when the switch is closed and have it turn on again as soon as the switch is opened?
Hope this makes more sense?

 

[NickDB]

Put the led across the switch? I will try this!

 

[NickDB]

Maybe this will make more sense?

 

[Javier Manzano]

It's much easier than all that. First you need to know how a diode works. Check this link:
http://electronics.stackexchange.com/questions/54977/how-does-a-diode-work

I don't really know what kind of circuit you have and why that diode is on even though it is not conected to the network, but in a nutshell, you have to make the current flow in the other direction. That is, connect the voltage source so that when you press the switch the current flows "against" the diode. Does it make sense?

In any case, if you send the squematic of the whole thing it would be much easier to help you and give you a complete answer (an squematic is something like the one I uploaded earlier).

Cheers,
Javier

 

[CDRIVE]

My nephew Marty is a tad dyslectic so I'll restate what he said a little differently. ....

Since you already have an existing LED and the limiting resistor, wire your switch across the LED.

Chris

 

[Martaine2005]

Thank you uncle Chris,
However, neither of us know what the load is! If the resistor will limit current / voltage to the load?

Your nephew, with love
Marty

 

[Harald Kapp]

Hmm, I wonder what would happen if you put the LED directly across the switch?
What do you think Harold?

I have a dejá vu.

 

[dorke]

Nick,
Here is the magic you asked for...
This little circuit simply popped in my mind(thanks for stimulating it).



All you need is add a little diode...
As you say the LED is 1.2V, while the diode is 0.7V... that is all it takes.

 

[NickDB]

Woow thanks! I think this is what im looking for.. I will try to replicate that circuit and let you know.. would you be able to tell me what kind of diode id need? shall i just type 0.7v diode in ebay?

 

[dorke]

Well,
You can actually use any diode(have you got any?).
From Ebay, buy 100PCS of 1N4007 they sell for less than 1$ (same price as 10PCS).
You will have a general purpose rectifier diode for future use.

 

[BobK]

As 2 other people have already suggested, you can leave the diode out in Dorke's circuit and it will work just as well.

And there is an even better solution. Use a normally closed pushbutton in series with the LED, resistor and battery. Pushing the button then breaks the connection and the LED is off without drawing any current like the other suggestions would.

Bob

 

[CDRIVE]

Bob's suggestion is the best way to go in our energy conscious world.

Chris