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Newbie level 4
Apr 2, 2011
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If i built a board for LED's using a resistor and a transistor what would cause the LEDS to emit very low power even when the program controlling them is off? I have a blue and a green LED very dim when everything is shut off. All the rest of my LED's are off when I turn the power off.

I dont have a multimeter with me so I cant determine anything, I eyed the board over and over again but seems like nothing is connecting.

I am sorry if I am not very descriptive with this post. If you need more info just let me know.

Thanks in advance.

It sounds like you have a leakage path somewhere in your system. My first thought is that your transistor is not fully turning off. Check that it's base is being driven low, and that no other circuit elements might be causing it to get voltage on it from a small current leakage. Adding a pull-down resistor, like 100k from base to emitter, might help?

Can you provide a schematic of the circuit you are using? Something drawn up in Paint would even be a place to start.

I was thinking the same thing, the problem with my board is that I made it very fast and very compact so im thinking maybe something (is like you said) leaking. Here is the diagram
This was just a prototype board, I eventually want to make something more durable and that can obviously not wear out so quickly.

Are you floating the inputs when "off" or are they pulled low?

Try 47k ohm resistors from the bases to emitter as mentioned, less than ideal construction might be giving you a higher ground potential to the transistors than at the microcontroller, if this is the case the 'off' brightness of the led's that are off will get worse when more led's are on.

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