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Why is my non powered arduino giving power to my lights? Answered

I am running an arduino uno to control three lights for a stop light costume (yes I got the idea from sparkfun. Sadly there will be no X-Bee in this project). These lights draw a pretty high current, so I have some mosfets on a proto-board to make it a little easier on my arduino. The lights are connected to digital pins 5,4,3. I have a power source at Vin and the thing is grounded at the ground pin right next to Vin. I have a switch grounding the arduino when flipped. When the switch is flipped the other way it gives me manual control, where there is a three way switch giving me the ability turn on and off whichever three series of leds I choose (all the leds are switched on and off via cathode being connected, not anode). The problem comes in here. When the proto board is attached I have control of the leds manually and everything is fine and dandy. Then When I attach the arduino, all three of the series of leds light up, until I switch back to automated mode(I haven't programmed the arduino yet so it just runs the las code, i.e. the pin 13 led blinks). I checked for short circuits and there are none. I am just wondering if there is a way to keep the arduino from connecting these things or should I just use the arduino or just use manual control.

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bwrussellBest Answer (author)2012-10-08

You can't expect any sort of predictable or controllable behavior until you program the Arduino. When you do that you can control the HIGH/LOW states of all the pins whenever the board is on.

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GenAap (author)bwrussell2012-10-18

Thanks, I made it so the arduino was always on and the problem just went away!

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Schwuuuuup (author)2012-10-08

Just a Guess: Maybe it has something to do with floating pins and you need a PullDown Resistor...

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steveastrouk (author)2012-10-07

What state are the arduino pins driving the mosfets ? I suspect they reset HIGH not LOW. Have you defined them in the Arduino code to do anything ?

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