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Turn ON led on open circuit

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me_guitarist

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can I use some transistor to make a simple circuit to turn on a led indication when the switch is opened? How? normally the led turned on when the swicth is close, how to do in oppasite?
 

turning on leds is easy

if its an analogue circuit

turn the led round and solder

whats the problem

are you stupid????:D like i was @ age 9 hehe

if you need help

im @ passport email simeon.webber@ntlworld.com

use msn

and ill help you learn
when i can and im online

msn you can send messages even when a person is offline

and vice versa
 

Hai me_guitarist,
This simple circuit answer your question.

68_1165456178.gif
 

Dear Budhy,
Is it a NPN transistor?

Added after 3 minutes:

I follow this circuit but it doesn't work...base voltage 12V also,I put 220K coz don't know how to calculate transistor,
my component:Q1=BC556B,
http://www.mayothi.com/images/transistor6.GIF[img]

[size=2][color=#999999]Added after 1 minutes:[/color][/size]
 

I follow this circuit but it doesn't work...base voltage 12V also,I put 220K coz don't know how to calculate transistor, my component:Q1=BC556B,


This circuit work!
R2=200K is too big, don't that resistor
R1= 1K chang with 560 Ohm
BC556B useable on this circuit
 

ok,R560 for R1. So whats the value for R2?3K9?
 

coz my input for R2 is 12V DC,the example used 5V DC on 2K
 

The problem is the led should be on if I din't giv supply to the base right? But the led doesn't turn on when I gave supply to the emitter & collector
 

me_guitarist, the solution is quite simple, you will need only 1 or 2 transistors to do the job depending your demand, but I understand that it is complicated for you since you do not understand transistor.

But in my turn, I do not know how to draw a circuit on this forum, I will learn about this but it takes me time (or very appreciated if anyone can instruct me). I hope can give you the circuit and and show how to choose transistor and calculate the resistors.

nguyennam
 

me_guitarist said:
Dear Budhy,
Is it a NPN transistor?

Added after 3 minutes:

I follow this circuit but it doesn't work...base voltage 12V also,I put 220K coz don't know how to calculate transistor,
my component:Q1=BC556B,
h**p://www.mayothi.com/images/transistor6.GIF[img]

[size=2][color=#999999]Added after 1 minutes:[/color][/size]

[img]h**p://www.mayothi.com/images/transistor6.GIF
Hi,
This design can't works!
The LED will remain ON, whatever the value of the input signal
R1=1k is efficient
R2= 47k (no more)
T1=BC556, 2N2907
The problem come from the input voltage, 5V is not enought to switch off the transistor.
The simplest way is to put a zener of 5.1V in serial with R2, the cathode connected to R2.
Sorry for expert in electronic, but this solution will work and it's easy to explain!


A+ Fishkiller
_________________
www.benito-design.fr
 

how to use this circuit to control magnetic lock?
I have a device which acting like a switch, built in NC & NO contact, I wanna use the NC contact & a LED as indication, when my device turn into NO, LED should lit up & release the magnetic lock.

Anyone got any idea?

Thanks in advance!

Added after 1 minutes:

it has to be using transistor
 

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