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Topic: LED trouble (Read 1 time) previous topic - next topic


I have 19 LEDs and 1 servo and 1 bluetooth module which I need to attach to an arduino duemilanove
I powered the servo of a seperate 5 V power supply (And I connected the grounds together(And the Servo works just fine))
But I just wanted to know if my arduino duemilanove can handle 19 (at least 15) LEDs when I connect the arduino to a 9V battery as it communicated wirelessly with the computer with a bluetooth module that needs 5 V power which will be powered of the arduino.
I will connect 3 LEDs to pin13 and 3 LEDs to pin12 and 3 LEDs to pin11 and 3 LEDs to pin10 and 4 LEDs to pin9 and 1 LED to pin8 and 2 LEDs to pin7 and a servo to pin6 and the bluetooth module to RX and TX.
Please reply


Assuming you're not using external drivers (you didn't mention any), and as long as you don't approach the absolute maximum per port current of 150mA and the package limit of 200mA, and you can accept that some LEDs will be dimmer than others, I don't see any problems.
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Plus the individual pin limit of 40mA


So everything would be just fine but maybe some will be dimmer


With that many LEDs and a 9V source available, you should connect the LEDs in series with a current limit resistor from the 9V supply, with an NPN transistor (2N2222 for example) on the bottom cathode that the arduino will control. Then you can get full brightness by having the same 20mA current flow thru a 'string' of diodes and have longer battery life, versus having the LEDs powered from 5V and having to split the arduino's 20mA/pin among the three LEDs and their seperate current limit resistors.
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