Hi Guys,

First time posting here, please bear with me. So I'm looking to wire a simple circuit. One 9v power source, a switch, a 91 ohm resistor, and two LED's (3.2v, 30mA).

I'm pretty sure this was correct with a simple switch but now I'd like to add a LED indicator switch. Here's the problem; it's a 12v switch (20mA@12v DC). Can I run a 12v switch on a 9v battery? How does this change what sort of resistance I'll need for the two component LED's? Do these types of switches generally have resistance built in? This is my first LED project so I'm still grasping the fundamentals.

The switch is Here

 

As long as the specs the switch exceed what you are switching you are good. Resitance of the switch is negligible and will make no difference in your circuit.

 

Thanks Spinnaker. Just a quick question to clarify. Since the switch has it's own red LED wouldn't that require some resistance to keep that LED from blowing? Will the light be dimmer because it's being powered by 9v?

 

Just connect the switch only to the 12v source. Measure the voltage and use that in your caculations. You can even pad the resitance a bit if ypu are concerned. It will mean a dimmer but longer lasting led.

 

Gotcha, so I guess I'll stick with the 91ohm resistor. That still comes after the switch since the resistance of the switch is negligible. Correct?

 

The led in the switch will have a voltage drop and there should be a resistor for that led. that will drop voltage so that is why you should measure the voltage with just the switch.

Be sure it is an led and not just a light but it really wont matter if you measure the voltage.