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Author Topic: Arduino Relay + LED  (Read 711 times)
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hello arduinos.


i'm new with the arduino board and started to do some experiments with it.
i'm trying to use this LED flashlight




starting from the basic example of Blinking LEDs available on the tutorial section of arduino.cc website.


here is the problem:

- if i connect the lamp to the port 13 the blink effect works but the brightness is very low.
- if i connect the lamp to +5v the brightness is ok but, obviously, the blink effect is not achieved


so... i tried to use a he721a0500 hamlin's relay to try to obtain the blink effect.
passing as input the pulse coming from the port 13 and the 5v electrical supply..as i hoped that in this way the component would work as a switch.

unfortunately it seems that won't work.
hope that somebody could help me (and that the problem explanation was enough clear)

thank you in advance.
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Your problem is that you have something like 10 LEDs, each wanting to pull 10-40 milliamps. Your Arduino output pin is only rated for about 40mA total and you really shouldn't hold it at that.

Fortunately there is an example in the playground...
http://www.arduino.cc/playground/uploads/Learning/multiple_leds2.jpg

The transistor at the bottom works rather like a switch, when the Arduino pin is high is turns on the transistor and lets the light shine.

Ordinarily you would need a current limiting resistor to keep from exploding your LED, but you seem to have verified that your flashlight won't pop at 5V.

Another note: I just guessed at the total current draw of your lamp, if I'm off by a factor of two then it will draw more than the Arduino supplies, so if you reboot when the light comes on... you know where to look. That can be handled if needed.
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