Need help with music and light project

Thread Starter

Zaper

Joined Aug 17, 2010
43
I am working on one of the projects in the book Electronics Projects for Dummies. This is my first electronic project ever and so I followed the books instructions and checked my design against every diagram I could but it still doesn't work.

What the project does is that it lights up groups of LEDs based on the pitch of a song that is playing (one group for high, one for low). It uses a microphone obviously and has 2 op amp ICs as well. I used a multimeter to check and make sure that the electricity was flowing everywhere it needed to and it was except for the wiring to the LEDs. The first LED had around .25-.5 of a volt (on a 6 volt circuit) and after that one there was no power. I assumed that that was ok since if there was power all the time then the LEDs would be on all the time which isn't the idea of the project. I thought maybe either the microphone or the ICs were defective.

does anyone have any ideas to help?
 

Thread Starter

Zaper

Joined Aug 17, 2010
43
Right now half of the lights work, the high pitched side if it matters. The other half will not. I think that it's a grounding issue though I can't figure out why. The LEDs connect to the breadboard through terminal blocks and then connect to a transistor and then to a resistor and then finally the ground. These are the same transistors and resistors that are on the other side and I have tried interchanging them between groups and the work fine. If I put the LEDs straight to the ground they light up and stay on which is a problem because they are supposed to flash. I checked with a multimeter and they receive no power but they do have the ability to because when I flip the switch to turn everything on they light up for a second or two.
 

marshallf3

Joined Jul 26, 2010
2,358
Not enough gain on the low end of the circuit, microphones tend to have poor low frequency response. Have you tried it right next to a blasting speaker?
 

Thread Starter

Zaper

Joined Aug 17, 2010
43
i did just try putting it in front of my computer speakers that I turned up pretty loud and still nothing. I did notice though that for some reason if I talk into the mic sometimes they will light up right when I stop talking. Don't know exactly what that means
 

SgtWookie

Joined Jul 17, 2007
22,220
Well, without seeing a schematic it's going to be difficult to give you much assistance.

Are you certain that you have used component values as specified in the book?
 

Thread Starter

Zaper

Joined Aug 17, 2010
43
heres an image of the schematic. the lower group of LEDs is the one giving me problems. as for correct component values do you mean like the right resistors and stuff? and if so then yes, they are the exact same resistors and transistors as I used in the working group
 

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marshallf3

Joined Jul 26, 2010
2,358
Since you actually got it to trigger once then it's probably just too low of a gain on the low fequency amplification. All but the better microphones tend to have a lower output with low frequencies and things such as cell phones have no low frequency output to speak of anyway.

If you have a list of the values I could suggest a component to change the value of. It could be one or both of two things - low frequency filter is designed for too low of a frequency or the gain just needs to be tweaked to hep equalize the response.
 

Dhruvang

Joined Aug 18, 2010
1
:)Dear try the different ckt for the same perpose....
we can make this circuit much more simple using microphone, opamp and different zener diodes...
I can give u that circuit...:)
 

Thread Starter

Zaper

Joined Aug 17, 2010
43
marshallf3: yeah i have a list of what parts were used and what the values for them are. theres obviously a lot of them so is there a specific area of the circuit that you want or just all of them.

Dhruvang: a new circuit would be nice but i don't think I can put together a circuit just from the schematic yet
 

marshallf3

Joined Jul 26, 2010
2,358
Since it appears to be the low frequency side let's look at the values of R25, 26 & 27 as well as C6 and what IC2 is.

I'll assume Q5-8 and R32-35 are the same values unless they're meant to switch on progressiveley as the music gets louder, regardles those values would be nice to know as well.
 

Thread Starter

Zaper

Joined Aug 17, 2010
43
R25 - 10 kohm, R26 - 1 kohm, R27 - 220 kohm, C6 - .1 microfarad ceramic, IC2 is a LM358 op amp, all transistors are 2N3904, R32-35 - 100 ohm

also R7 and R24 are 10 kohm potentiometers and are used to control how touchy the mic is
 
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marshallf3

Joined Jul 26, 2010
2,358
Approximately half the value of C6 or/or double the value of R27.

Reducing C6 will lessen the amount of low frequency it filters out, increasing R27 will increase the gain of that filter circuit.

Good staring points anway, see if it makes any noticeable difference and go from there. If you reduce C6 by too much it will eventually make the low frequency side too close to the high frequency side and reduce the capability of being able to distinguish between the two, if you increase R27 by too much the amp will evntually become too sensitive and could possibly oscillate depending on the circuit layout, causing all the LEDs on that side to stay lit up.

If R32 - 35 are 100K ohms I don't quite see how enough current would ever get to the LEDs though, an LM358 op amp IC is capable of sourcing 40 mA of output current, plenty enough to drive the transistors, but 100K isn't anywhere near low enough to allow sufficient current through to run the LEDs off of 6V.

What are the values on the other side for these resistors ( R15-18) - 100 ohms would be more in line allowing somewhere between 20 - 30 mA per LED.
 
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Thread Starter

Zaper

Joined Aug 17, 2010
43
sorry my bad. R32-35 (as well as R15-18) is only 100 ohm not 100 kohm

If i were to half C6 and double R27 would that help even more or just cause the problems you talked about before?
 
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marshallf3

Joined Jul 26, 2010
2,358
sorry my bad. R32-35 (as well as R15-18) is only 100 ohm not 100 kohm

If i were to half C6 and double R27 would that help even more or just cause the problems you talked about before?
Until you really got to extremes simply lowering C6 or upping R27 aren't going to hurt anything. This will simply be a matter of getting the gains more balanced between the high and low frequeny sides. You may have to go a lot further than just doubling R27, might need to go all the way up to 1M and if that doesn't do it we may have to tweak R26 as well.
 

Thread Starter

Zaper

Joined Aug 17, 2010
43
Ok so I took C6 from a .1 μf down to a .047 μf with no noticeable difference. I also tried making R27 a 1m ohm and also 470k ohm (originally 220k ohm) and the LEDs turned on and stayed on

Also to try in between 220k and 470k I tried running two resistors in parallel. I tried 1m + 470k which by my calculations is around 320k and also 470k + 470k which I think is around 235k. For both of these the lights turned and stayed on also.
 
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Thread Starter

Zaper

Joined Aug 17, 2010
43
I did try changing R26 as well. The only change I saw was that when I turned on the circuit the red LEDs would turn on for a couple seconds and as I upped R26 more and more they stayed on for shorter and shorter times
 

marshallf3

Joined Jul 26, 2010
2,358
Now I'm not so sure that amp IC has ever worked properly from the start. The circuit is simple and with those type changes it shouldn't be acting that way.
 

Thread Starter

Zaper

Joined Aug 17, 2010
43
so should I just replace the IC or is the circuit wrong?

also I did do some looking and it turns out that the recommended mic has a sensitivity of around -40 dB and mine has -50 dB. I know that that's a big jump on the dB scale but will that make much difference?
 

marshallf3

Joined Jul 26, 2010
2,358
Forget the mike as your other side is respnding. The circuit looks to be fine so I am starting to suspect the IC, it could actually be either of them causing the malfuntion.
 
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