Hi All,

I wanted to do a simple circuit whereby a LED can be turn on & off using contact limit switch.

Question 1
I've connected like below image, why the battery become HOT? does it because I did not connect any ground?

Question 2
Where do I put the LED Anod & Catod if I wanted to make the LED on when the switch is closed?

 

Hi azhan,
Without a resistor, the battery will get HOT!
Look at this modified circuit.
The resistor value will depend upon the LED type, what LED do you want to use,?

E

 

Hi azhan,
Without a resistor, the battery will get HOT!
Look at this modified circuit.
The resistor value will depend upon the LED type, what LED do you want to use,?

E

Hi eric,
I dont have the LED details but it requires 3V as what the shop says and the LED diameter is 10mm
what resistor should I get?

 

hi,
Driving a 3v LED from a 3v battery will not give the result you expect.
Even though the LED has typical 3v forward voltage drop, they can have a voltage range of +/-10%
Also the battery will discharge below 3v when on load.
What is the specified operating current of the 10mm dia LED.? and the type of battery.?
E

 

You have to modify the wiring first.
The function of Pins of limit switch:
1. N.C - Normal Close
2. N.O - Normal Open
3. COM - Common pin

Question 2
Where do I put the LED Anod & Catod if I wanted to make the LED on when the switch is closed?

The COM pin connected with N.C pin and then they are in the shorted situation, so you should exchange the pin N.O an N.C.

I dont have the LED details but it requires 3V as what the shop says and the LED diameter is 10mm

You could use the circuit as ericgibbs provided, but you have to exchange the the pin N.O an N.C.

3V/10mm led then current could be 10mA, 3V battery to a 3V led is not a common method to use, but you can try a 10Ω 1/4w resistor to protects the led, if it can light up the led then you can try to using the bigger resistor, adjust the value of resistor and brightness, until you get satisfaction.