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Topic: 10 RGB leds - all doing the same (Read 4 times) previous topic - next topic

Chagrin

It is with external power. The grey wire connecting to the "9V" pin (which should be labeled "Vin") is directly connected to the power jack and "unregulated" (not regulated by the Arduino which only regulates the 5V and 3.3V pins).

Transistor tutorial; it's worth 10 minutes of your time: http://www.kpsec.freeuk.com/trancirc.htm


johnwasser

> 1. is that mean that i need 30 NPN transistors...?  :smiley-eek:

No, you need one transistor per GROUP of cathodes.  Since you have three groups of cathodes (reds, greens, and blues) you need three transistors, like in the LED strip example you found.  Each cathode will need a current limiting resistor.  That is EACH cathode so you will need 30 resistors.
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CrossRoads

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Justniv

Thank you all,
Quote
It is with external power. The grey wire connecting to the "9V" pin

1.so for external power, is it gonna be ok to take this: http://www.dipmicro.com/img/1/DCA-FULLVIEW.jpg
cut his adapter-then i'll have two wires-so i'll connect one to "GND" pin and the other wire to "Vin" pin?
(im planing to do it with an old charger like nokia phone charger - but with the right properties)

2. The NPN, what do i need to know about it in the datasheet?
which one will fit the best:
http://www.taydaelectronics.com/2n3904-npn-general-propose-transistor.html
http://www.taydaelectronics.com/2sc945-c945-bipolar-transistors-npn-50v-0-15a.html
http://www.taydaelectronics.com/2n2222a-2n2222-npn-transistor-0-8a-40v-to-18.html
and whats are the purpose of each one, i mean whats the differences?

3. just out of curiosity, insted of putting a resistor in every led, can't i put "high" resistor at the emmiter of each NPN? i mean between GND and Collector&Base "junction".

again thnak u all i apriciate your help :)
CrossRoads special thank for the sketch pic


johnwasser


3. just out of curiosity, insted of putting a resistor in every led, can't i put "high" resistor at the emmiter of each NPN? i mean between GND and Collector&Base "junction".


No, you can't.  Ten LEDs draw ten times the current of one LED but if you put 10 LEDs in parallel and feed them ten times the current there is no way to make them share the current equally.  Some devices will hog the current, overheat, and die.
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