I built this circuit using a red led ,a tip131 transistor and a battery of 3.7 volt. Nothing happens. But if i Connect a dc motor from a cd player in parallel with the led it works. How is it possible? What the dc motor does to the circuit?

 

Leds wired in reverse, also you need a series resistor in each led.

 

Does dc motor invert polarity?

 

No, just goes in the opposite direction....

 

And it would affect the led... Anyways led is wired perfectly. Maybe is it wrong the circuit?

 

Put the leds across the battery, both ways round, see which way they work...

 

It's very strange because the led starts blinking only when i Connect the motor in parallel with it

 

The image is so small and fuzzy that there is not any detail. Please post one that is larger and more clear. Are there any resistors in the circuit anywhere?

ak

 

No resistors. I found the image on the net. Sorry

 

What's with the headphone connector attached to the base and emitter?

It's a very odd looking circuit. Where's the current limiting resistor for the LED's? Where's the base current limiting resistor? Where does the headphone connector go?

Your motor is providing a resistance between the collector and emitter and saturating the base of the transistor, it's in open circuit without the resistance of the motor coils.

 

Leds need a series resistor to work properly, otherwise they will burn out, try putting one of them across the battery with a 100 to 470ohm resistor in series.

 

The headphones connector goes into an mp3 ipod . I plug it to the output of an amplifier.
When there's a peak of 0.7 volt the led start to blink. But without a resistor the led will burn. Thank you guys.

 

The headphones connector goes into an mp3 ipod . I plug it to the output of an amplifier.
When there's a peak of 0.7 volt the led start to blink. But without a resistor the led will burn. Thank you guys.

So it's like a VI meter?

 

It's bass syncing. Not so sensitive but nice to see

 

I'm sure there are plenty of other circuit examples out their in the googleverse that'll actually work. The one you've posted lacks some fundamental components and I'm not suppressed it doesn't work.

 

Can someone draw me a circuit that use a 5 volt source using a transistor a red led and all the necessary components? Thanks

 

The audio souce is from a Pam8403 max 3w running on 5 volt.