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Topic: Question on LEDs and Speakers (Read 1 time) previous topic - next topic

thomas3120

May 24, 2012, 12:08 pm Last Edit: May 24, 2012, 12:12 pm by thomas3120 Reason: 1
Hello,
Working on my robot and recently added a speaker along with my iPod (for the time being) to create sounds and voice.
I'm using the internals of a desktop speaker and have enough volts and current to power the amp.
I added 2 clear LEDs to light up when there is sound or voice from the speaker.  It works well but I have to have all the volume levels maxed out to get a decent effect.  It works really well but it's really loud...

Was wondering if I could add a amplifying transistor (hmm...at the LEDs?) to get a better result while not going over the rated volts/current of the LEDs?
I tested the volts (using my DMM) and the volts fluctuated around .5 to 1.0V when there was sound present.

Any suggestions would be appreciated,
Thomas

*EDIT:
I just remembered reading up on the TIP31 transistor, wonder if this would help me out.

pYro_65

#1
May 24, 2012, 01:51 pm Last Edit: May 24, 2012, 01:53 pm by pYro_65 Reason: 1
A transistor could be used, but the brightness may still go too low with quiet stuff. You would have to find out the highest possible speaker voltage used so you can calculate the base resistor and don't overpower the LED.

I would look at threshold level detector circuits using op-amps or transistors, then you can make the LED's turn on to full power when any audio is played above a threshold, quiet or loud.

thomas3120


A transistor could be used, but the brightness may still go too low with quiet stuff. You would have to find out the highest possible speaker voltage used so you can calculate the base resistor and don't overpower the LED.

I would look at threshold level detector circuits using op-amps or transistors, then you can make the LED's turn on to full power when any audio is played above a threshold, quiet or loud.


Ok, will do :)
& thanks for the reply

Thomas

SatCure

This is really simple stuff. A silicon transistor will begin to turn on with a base-emitter voltage of around 0.6 volts. So your voltage range is ideal.

Connect an NPN transistor (e.g. 2N3904) emitter to the common (0v) rail of your amplifier.
Connect its base via a 1k resistor to the "live" amplifier output.
Connect its collector to a 1k resistor. Connect the resistor the the LED cathode. Connect the LED anode to a power supply voltage or battery of between 6v and 12v DC.
Connect the PSU negative to the common (0v) rail.

The resistor values are for starters. You may need to decrease them to get full brightness.

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