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(SOLVED) Break circuit = Make circuit?

Basically, what I want to do is activate something when there is no current somewhere else.

Examples of uses of this would include turning an LED on when there is no light on an LDR and turning it off when there is light, rather than the other way around, along with turning an LED on when a circuit is broken by opening a door.

Apologies if I have not been clear enough.

Is this possible? 

EDIT: Thanks to NachoMahma, I have it set up with a transistor. I will post a schematic if anyone is interested.

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NachoMahma6 years ago
. It seems the system ate my previous comment.
.  Use a relay with a NC (normally closed) contact.
__DELETED__ (author)  NachoMahma6 years ago
Thank you for your reply.
But what exactly is a relay? I am quite a beginner in electronics.

Thanks again,
~H4ZZ
.  A relay, in a nutshell, is just a switch with an electromechanical actuator. Google is your friend (and should have a picture or few).
.  For the low-voltage, low-power example you gave, a transistor (Google is your friend) may be a better option.
__DELETED__ (author)  NachoMahma6 years ago
Okay, so I would need a Single Pole Single Throw, Normally Closed relay for this?
I do have a transistor, so how would I use it like this?

Thank you again,
~H4ZZ
. Yes. A SPST/NC would be perfect. You could also use the NC contacts on a SPDT (or DPDT).
.  It depends on the transistor. If you can find a part number (probably looks something like 2Nx..x, eg, 2N414), you should be able to easily Google the specs.
__DELETED__ (author)  NachoMahma6 years ago
Great, thanks for your help.
I'll have a look tomorrow....

Thanks again for your help,
~H4ZZ
__DELETED__ (author)  __DELETED__6 years ago
Thank you for your help, it works. I have my circuit set up on a breadboard and it works for both scenarios I gave as examples.

Thanks again,
~H4ZZ
Yes, its very easy to do. You can find anynumber of circuits on line for what you want to do.
__DELETED__ (author)  steveastrouk6 years ago
Thank you too for your reply.
How would I go about finding one of these circuits?

Thanks again,
~H4ZZ
Put the words "light activated switch circuit" into Google.
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