HI, I've searched the forums and can't seem to find an answer. I have a talking chess computer, I added four LED lights based on this circuit design:

http://www.instructables.com/id/Creating-An-Audio-Reactive-LED-Circuit/?ALLSTEPS

The idea is that they respond to the computer 'talking' The problem that I'm having is that the LED's are lit brightly all the time, they flicker slightly when the computer talks but not at all the effect I was hoping for. I wanted the LED lights dim way down or even off until the voice is activated. I have the base of the transistor connected to the positive terminal of the speaker. I was not sure what is triggering the transistor when there is no sound out of the speaker. I added a resistor in line from the speaker to the base hoping it would turn the LED's off until the computer talked but it only dims all the leds and does not affect the trigger point. Any advice for me? I'm a hobbyist/novice so take it easy on me. Thanks so much!!!

 

If anything you could try to pull the transistor base low with a resistor to common. That would keep it off until a large enough noise trips it.

The article says that an amplifier would do a better job. You can't expect much from such a simple circuit.

 

Thanks, I will try it and see what happens. I actually believe things were working better when all of the was on the breadboard. I think my expectations are low enough, I just want the lights to flicker somewhat in response to the audio. Many people are using these very simple circuits to achieve what I desire, you can see the video on the posted link shows very nice results with it.

 

Use jumpers if you already have it soldered, You don't want a lot of resistance to positive voltage on the base or it will never trip. A resistor divider to the base pulls the voltage down proportionally.

 

HI, It's working perfectly now. I actually have it differently then show in the link. My LED's are hooked up to the emitter instead of the collector. Then instead of the collector going to ground I moved it to the negative terminal of the speaker and that is when things started working correctly. Is it a problem that I have the collector and emitter reversed? The brightness is about what I want it and I'm already using larger resistors then stated for the array. Thanks

.....Ok, I see it's bipolar and can be used as a switch or amplifier, with my 9v supply I don't need it amplified so I guess everything is good now.

 

The sound coming in is AC, so it could work either way as long as it is configured properly. The NPN collector is ahead of the emitter which is closer to common.
The LED could be on either side of the transistor too.

 

OK, Thanks for your help on this, your talk about the common promoted me to reconfigure things and get to a solution. Now I may try to have the LED's fade out. I see there is a lot of information on that topic in the forums here.