Hey guys,

First off I'm brand new to these forums and the site/forum is really helpful!

I guess to start off, I'm trying to build a a color organ that has low frequencies flashing a red LED, mid flashing a green LED, and high frequencies flashing a blue LED. (think its called a 3-channel?)

Anyway, so far my instructor has been helping me design the low, mid, and high pass filters. As for the LED's, I just want them to be "instant on" and "instant off". They dont need to have dynamic lighting when sound levels are low or high. Just basically on and off. Just need to be simple as can be. And the frequencies dont need to be EXACT for the lights, just like a simple rough color organ. But obvious that highs, lows, and mids are separated.

My instructor mentioned about using a peak detector of some-sort. I'm not really too sure on what i can do/use after separating the frequencies before the LED's.

ANY help will be GREATLY appreciated!!!

I attached the schematic

 

Your schematic does not appear to have successfully linked. Can you see it?

hgmjr

 

Our OP is the only one who can see the schematic, as they tried to post a link to an Email in their Gmail account; which doesn't work for the rest of us.

You need to attach the image to your post.
Edit your original post, click the "Go Advanced" button, then click the "Manage Attachments" button, and then select the image file to upload from your hard drive.

PNG format files are preferred; they are compact, require no extra software to read, and are not "lossy" like .jpg format files.

 

Our OP is the only one who can see the schematic, as they tried to post a link to an Email in their Gmail account; which doesn't work for the rest of us.

You need to attach the image to your post.
Edit your original post, click the "Go Advanced" button, then click the "Manage Attachments" button, and then select the image file to upload from your hard drive.

PNG format files are preferred; they are compact, require no extra software to read, and are not "lossy" like .jpg format files.

whoo thanks! sorry about that. picture attached!

 

This is meant for 12 VDC.

This has not been built yet, something I'm going to be trying out eventually.

U3 - LM393
U4 - LM358

You'll need 3 of them, the 555 can be shared, and the op amps can be low quality quads, along with a quad comparator.

Since you plan on having a dual power supply this design can be simplified quite a bit. Since I was thinking of a single polarity power supply I had to make a pseudo ground.

 

I would have used a full precision rectifier described here http://sound.westhost.com/appnotes/an001.htm
I think the one in figure 6 will do fine. Apply this on the input before filter stages. But you have to recalculate the filters. The rectifier will double all frequencies. After the filter stage you apply a comparator. So then the output from the filter is higher than a certain level, you light the LED. The comparator setup should be adjustable so you tune the system for your music

 

Thing is, I think it is adding complexity with no benefit. The RC circuit formed by R12 and C5 is already long enough you won't be able to tell the difference, and if it is too short simply increasing either will lengthen it out to whatever you need. I calculated for 10Hz, then rounded dramatically. Figure 7 means 3 more op amps and associated circuitry, and the only place it *might* make a difference is the low frequency side of the color organ.

CR3, U4b (if there), R12, and C5 is the peak detector.

**********************

I thought seriously about reversing the peak detector (U4b) and the amp (U4a). The advantage of using an op amp based precision diode is there is no diode drop, it is divided by the gain of the op amp. I don't know if the sequence makes a difference or not.

I also didn't catch this part...

Anyway, so far my instructor has been helping me design the low, mid, and high pass filters. As for the LED's, I just want them to be "instant on" and "instant off". They dont need to have dynamic lighting when sound levels are low or high. Just basically on and off. Just need to be simple as can be. And the frequencies dont need to be EXACT for the lights, just like a simple rough color organ. But obvious that highs, lows, and mids are separated.

My idea is definitely dynamic, amplitude controlled by intensity.

The comparator with a pot instead of the 555 triangle wave generator would do simple on/off. You could use Example A in that case. I think the dynamic approach is a lot more dramatic though.

 

Your schematic for the Color Organ uses LF357 opamps that are obsolete and have not been made for 11 years (1999 was the last production).
The schematic shows most opamps with a gain of 1 and one opamp with a gain of less than 1 but the datasheet says that an LF357 is de-compensated so its minimum allowed gain is 5. Therefore the circuit will not work as shown.

 

Where are you seeing LM357? I listed LM358, which are dirt cheap and just as common. The diode circuit might need something in the way of frequency response (I don't think it need much), but fidelity is not an issue.

 

Where are you seeing LM357? I listed LM358, which are dirt cheap and just as common. The diode circuit might need something in the way of frequency response (I don't think it need much), but fidelity is not an issue.

The OP used lf357 in his circuit. It is correct that LF357 is obsolete. But this is a school project so it does not matter.

 

The original circuit is a color organ that has audio filters.
It uses opamps that are obsolete and will not work in that circuit (because they are de-compensated). School kids should make circuits that work properly and learn why this one won't. Maybe I shouldn't have said why. Maybe the teacher wants the kids to find out why the circuit does not work.

Bill's circuit dims and brightens the LEDs (with PWM) by the loudness of the music. But the OP wants the LEDs to be simply turned on and turned off, not dimming and brightening.

 

Your schematic for the Color Organ uses LF357 opamps that are obsolete and have not been made for 11 years (1999 was the last production).
The schematic shows most opamps with a gain of 1 and one opamp with a gain of less than 1 but the datasheet says that an LF357 is de-compensated so its minimum allowed gain is 5. Therefore the circuit will not work as shown.

I had missed it entirely. Nice catch.

Could have been worse, 741's for example.

 

The circuit will oscillate at a high frequency if old de-compensated LF357 opamps are used.
It will work if old 741 opamps were used but the high audio frequencies above 9kHz might be reduced.

 

Hey guys thanks for the responses!!

As for the obsolete op-amps....yea my instructor is OLD SCHOOL. So I'm not surprised. But yes the LF357's are obsolete, and my instructor said to get the LF347's (which i guess arent any better)

Here's the thing, I wasn't really too sure on how to attack this project in the first place, I just knew I needed to create filters for the frequencies, and have those light up some LED's. But just didn't know what parts to use (op-amps) etc etc. So my instructor etched up this diagram to help me out.

Do you guys know what simpler designs I can use for this project? I'm not required to have any certain parts used in the project. So basically, just build it and make it work and I pass. So with that, I don't know if it will be easier to just assemble a circuit that just turns the LED's instant on and instant off or have it fade with the intensity of the music? Just whatever is easier =)

Oh and Bill, I might give your circuit a shot on a breadboard to test it out. Just need to get the parts! Thanks for the schematic!

What do you guys think? Thanks again!

 

We have presented some design solutions. Discuss it with your your teacher. He will probably understand that internet is your schematic source. But as long as you learn something. Will how you got your design be irrelevant

 

We have presented some design solutions. Discuss it with your your teacher. He will probably understand that internet is your schematic source. But as long as you learn something. Will how you got your design be irrelevant

Will do!

Btw in Bill's circuit that was presented..is that an IGFET (MOSFET) in between the LED's and R5?

 

A nMOSFET, conventional model. Something like a IRF510 (though that is worst of class), which is available at Radio Shack.