LEDs on Rotary Switches | Resistors for each switch or LED?

Thread Starter

OneTrickJester

Joined Dec 14, 2016
10
Hi there,

I am going to make an ABC|XYZ switch, I already understand how to wire everything, but I am a little stumped on the LEDs.

I've read that you need to use a resistor for each LED in a parallel circuit. However I feel this situation may be slightly different. The device is going to use two 4P3T rotary switches to select input and output devices, with 3 Poles being for Left Right and Ground, and the fourth pole being for the LEDs. To me it seems that the poles are in parallel, and therefore I would only need a resistor for each switch as opposed to each LED.


So will this work fine? Or am I going to burn out my LEDs?
 

ErnieM

Joined Apr 24, 2011
8,377
That will work just fine, unless you have a "make before break" switch where as the switch is turned two poles are connected before one is released. Even then there will be no damage just the LEDs make both dimly light for that instant (which could be a long time if the switch is turned very slowly).

Sorry... Bit of a stream of consciousness there, it is a good circuit.
 

Thread Starter

OneTrickJester

Joined Dec 14, 2016
10
That will work just fine, unless you have a "make before break" switch where as the switch is turned two poles are connected before one is released. Even then there will be no damage just the LEDs make both dimly light for that instant (which could be a long time if the switch is turned very slowly).

Sorry... Bit of a stream of consciousness there, it is a good circuit.
Awesome. Thanks for the reply! Now all I need is for all the components to arrive from China.
 

Reloadron

Joined Jan 15, 2015
7,501
As long as all of the LEDs are the same that is fine. However, if for example you have a red, green and blue LED, LEDs not the same with different current requirements then you would want a series resistor for each LED but as long as the LEDs are all the same then what you have will work just fine.

Ron
 

Thread Starter

OneTrickJester

Joined Dec 14, 2016
10
As long as all of the LEDs are the same that is fine. However, if for example you have a red, green and blue LED, LEDs not the same with different current requirements then you would want a series resistor for each LED but as long as the LEDs are all the same then what you have will work just fine.

Ron
Thanks for the reply! I knew this already, but it is good for anyone that may come across this in the future.

I'll be using all red LEDs for indicators for this project, so the schematic I drew should match pretty close to what I make once I have all the components. Due to this I'll also be able to use higher voltage LEDs (Green, Blue etc) but they'll just be significantly dimmer.

For any future readers:

To find the right resistor you use Ohms law. A 3v 20mA LED, powered by a 6v source, needs at least 150ohms of resistance (v / I = R).

You can also use Ohms Law to find the actual current. If you are using a 3v LED with a 150 ohm resistor, on a 5v source, you will have 13.3mA of current, which will make the LED a lot dimmer than it would be with a 100 ohm resistor (which is the minimum for a 3v on a 5v supply).

TL;DR
To find the correct resistor for your LED and supply (Source Voltage - LED Voltage) / LED Current = Resistance in Ohms
 

hp1729

Joined Nov 23, 2015
2,304
Hi there,

I am going to make an ABC|XYZ switch, I already understand how to wire everything, but I am a little stumped on the LEDs.

I've read that you need to use a resistor for each LED in a parallel circuit. However I feel this situation may be slightly different. The device is going to use two 4P3T rotary switches to select input and output devices, with 3 Poles being for Left Right and Ground, and the fourth pole being for the LEDs. To me it seems that the poles are in parallel, and therefore I would only need a resistor for each switch as opposed to each LED.


So will this work fine? Or am I going to burn out my LEDs?
You need to reverse the battery polarity, but in general, yes the circuit is good.
 

Thread Starter

OneTrickJester

Joined Dec 14, 2016
10
You need to reverse the battery polarity, but in general, yes the circuit is good.
My bad. Forgot to flip the voltage source in the schematic. Thanks for pointing it out. I will actually be using a USB cable to supply the power, as it is a stable 5v source and I can make them as cheap as $2.54 per 6'.
 
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