Add LED to 12v in to show when the power is on?

Other Hardware General Electronics
1

Hi,

if I want to add a LED to a 12v in line to show when the power is on, is it a simple case of adding the LED and appropriate resistor in parallel with the line?

2

12V -> LED anode.. LED cathode(flat side) .-> resistor.. resistor -> 0V (GND)

Resistor value 1000 Ohm +/-

3

Thanks

4

Might I add that this may want to be temporary.

The "pilot" light on the Arduino boards often becomes a nuisance. You usually only want to monitor the power input when prototyping. In times past, keyboards had a "power" indicator but no longer - though admittedly, the "NumLock" indicator generally fulfils this function anyway.

5

Paul__B:
Might I add that this may want to be temporary.

I've never been involved in the development of a product that hasn't had a power on LED. Many of the products I've helped build have also had a little button that can be pushed to force an illumination of the LED so that it could be tested to make sure it wasn't broken. Power on LEDs are a good idea.

knut_ny:
12V -> LED anode.. LED cathode(flat side) .-> resistor.. resistor -> 0V (GND)

Resistor value 1000 Ohm +/-

Exactly. I would add that the way to calculate this is

R = (V - 1.7)/0.01

where R is the resistor value you want to calculate, V is the voltage - in your case 12 - the 1.7 is the voltage drop across a LED (the ones I use anyway so check your data sheet), and 0.01 is the amount of current (10 mA) it takes to illuminate the LED (again check your data sheet). So in your case:

R = (12 - 1.7)/0.01 = 1030

So knut_ny was on the money.