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Can someone help me with common cathode leds and push buttons? Answered

Hello everyone!

Im planning on doing a thingy like this for my son, can it work?

Im going to use a 3V 1A power source to connect 3 push buttons to a common cathode led, like on the image included.

I was planning to use this led:
http://www.ebay.com/itm/2p-10mm-RGB-LED-Common-Cathode-4-Pin-Tri-Color-Red-Green-Blue-3v-6v-9v-12v-FCL4P-/290802586540?hash=item43b52f53ac:m:m6IDFR2pATn4PfCbuH-kqzw

and switches like this:
http://www.ebay.com/itm/152146897080?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
is says: Light Voltage DC 3V

In my mind it looks like this: if u push the red, the led will turn red, and u can add additional colors to it with the other 2 buttons.

Could this work?

If I figured it out good, I wont need a resistor for the blue and green, but I will need one for the red. How big it should be?

Is it a good setup that I solder the positive to the switches and the black/negative to the one led?

Can I add an another lead from the power supply to an another independent switch and single color led?


Discussions

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Smitiz

2 years ago

Well maybe I should use a 5v power source instead then :)

I wont use batteries, ill use an old 3V phone charger, or the old Nokia charger I found today (5V 350mAh)

Ill use resistors before the leds with the recalculated Ohms law.

Wont the led switches draw away from the voltage?

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ThirdEarthDesign

2 years ago

The LED you plan to use is a RGB LED, it is effectively 3x LED's in one, with a common cathode (negative / black wire) and an anode (positive / red wire) for each colour (R,G and B). As long as you wire up the pins correctly, your circuit will work.

With regards to resistors, although the Green and Blue have the same forward voltage as your battery source voltage you should still use a resistor, use a 1ohm resistor on each of these.

As for the red, use a 47ohm resistor.

This is all based on a forward current of 20mA.

The eBay item you're looking at apparently comes with the resistors as well. Your choice of switch will work just fine.

You can connect your battery to as many switches/LEDs as you want, just means you will run the battery down quicker (though LEDs consume very little power anyway).

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Downunder35m

2 years ago

Do a Google search for LED resistor calculators.
Otherwise you can use the data for the LED color in question and Ohms law to calculate the resistor needed.
3V might be too low for green and blue colors as most require around 3.2-4.2V for full brightness.
Again, should be specified for your LED and each color.
Something like 2.6V and 26mA for example.