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Need help with very basic task(atleast i hope)

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etmdesai

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Ok, I am an aerospace engineering student trying to build a awesome beer pong table. One of the components is having LEDs flashing to the music. I tried looking for a good color organ schematic but everything only powers 4 leds. I want to try to use atleast 50 or so leds or maybe even a couple of neon light sticks. I tried putting a led strip to my speaker system, but i would have to turn up the volume really loud just to get it to flash dimmly. That led strip is 12 volts. What is a good way to try to tackle this process.
 
Ok, I am an aerospace engineering student trying to build a awesome beer pong table. One of the components is having LEDs flashing to the music. I tried looking for a good color organ schematic but everything only powers 4 leds. I want to try to use atleast 50 or so leds or maybe even a couple of neon light sticks. I tried putting a led strip to my speaker system, but i would have to turn up the volume really loud just to get it to flash dimmly. That led strip is 12 volts. What is a good way to try to tackle this process.

Hi and welcome to the forum!

First, I should mention that you should pick one area of the site to post a question, and not post the same thing in multiple places. Having just one thread about a topic makes it *much* easier to keep track of things--you don't have to try to remember who said what in which thread. :)

Plus somebody might jump down your throat for cross-posting, which is never pleasant.

Anyway, on to your actual question. I'd say that a colour organ is indeed what you want, and use the 3 or 4 lamp outputs from one of the schematics you've found to drive power transistors to control the large numbers of LEDs you need.

For example, say you had a 3-lamp colour organ circuit which would light up a red lamp for bass frequencies, a yellow lamp for mids, and a green lamp for highs. Instead of driving those 3 lamps directly, you'd take the output from the circuit for the red lamp to drive one (or more) power transistor or MOSFET to control a whole bunch of LEDs from the bass frequencies. You'd do the same thing for the mid channel and the high channel.

Mixing the neons and LED strips in might complicate things slightly but I think not horribly.

The actual values you'd need would depend on a lot of things, such as the colour organ schematic you planned to use, the power source you have available (voltage and current ratings), how many LEDs you want to drive and what kind of LEDs they are (different colours and types have different voltage and current requirements), and so on.

So, my first question to you would be: are you OK with having say 3 channels as I just described, with say 20 LEDs for bass, 20 for mids, and 20 for highs?

My other questions would be:

1. What kind of experience do you have constructing/designing electronic projects?
2. What is your timeline for this project?
3. What is your budget for this project?

And before we get too much farther, I'll add my standard disclaimer here: I'm a computer programmer--I am not an electrical or electronics engineer, nor do I play one on the Internet. ;) I will try to help as much as I can but I'm just a hobbyist; there are others here with vastly more experience and knowledge than I have. But I can help you to get together the information you'll need to get the answers you want.


Good luck!

Torben
 
Hey Torben,

Ok, after doing more research it seems that what i want to do is NOT infact a color organ. From what it seems like a color organ is when you have seperated low-mid-high with bandpass filters and all I really need to do is to get the amplitude or just the low bass. My timeline is like a month-ish and budget is about a hundred dollars. I do not have much experience, but I am learning pretty quickly.

I would like to try to attempt a graphic spectrum analyzer with the LEDs, but i think that would be getting in way to over my head..
 
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Hey Torben,

Ok, after doing more research it seems that what i want to do is NOT infact a color organ. From what it seems like a color organ is when you have seperated low-mid-high with bandpass filters and all I really need to do is to get the amplitude or just the low bass. My timeline is like a month-ish and budget is about a hundred dollars. I do not have much experience, but I am learning pretty quickly.

I would like to try to attempt a graphic spectrum analyzer with the LEDs, but i think that would be getting in way to over my head..

You said in your other thread that you want to skip the filters because you just want to trigger the lights on amplitude. What kind of music will you be playing? I assume it's going to be fairly high-energy. If you want to have the lights pulse in time with the music you would be better off triggering off the low frequencies only--most modern pop rock music is compressed to within an inch of its life and you may be surprised at the result. i.e. it might be difficult to get the lights to reflect the pulse of the music as you perceive it when you listen. It might be even harder to get it to perform well over a range of different program material.

I'd still recommend the one-channel colour organ, which would help you get around that problem. Then again, you might be using music which has enough dynamic range that this isn't a problem.


Torben
 
Yeah the type of music isn't going to be modern rock. Although thats the usual genre i listen to, this will be mainly used doing partying so hip hop and the occasional techno would play. When i tried my really basic attempt to doing this. All i did was connect the LED directly onto the speaker and it flashed to the beat, but very dimmly. So if it was really dim with only two LEDs, powering 50+ would be really hard through that method. That being said I looked at a color organ schematic and thought it would be possible connecting three low band pass filters and instead of having low-mid-high that way i can connect 20 or so LEDs to each channel?

How hard would it be to try to get a spectrum analyzer going. I heard that the IC i would need would be a lm3914 or a lm3915. I have a electrical engineering professor who would help me, but i would have to do most of this research and all i have to do is show him the circuit that i would be building and he would lend me a hand when he had time. The only thing is that i have to put most of it together before i show him.
 
Yeah the type of music isn't going to be modern rock. Although thats the usual genre i listen to, this will be mainly used doing partying so hip hop and the occasional techno would play. When i tried my really basic attempt to doing this. All i did was connect the LED directly onto the speaker and it flashed to the beat, but very dimmly. So if it was really dim with only two LEDs, powering 50+ would be really hard through that method. That being said I looked at a color organ schematic and thought it would be possible connecting three low band pass filters and instead of having low-mid-high that way i can connect 20 or so LEDs to each channel?

Yes, that should work, although I'm unclear on why you want 3 low channels instead of of just one low channel or 3 separate channels for the lows, mids, and highs.

How hard would it be to try to get a spectrum analyzer going. I heard that the IC i would need would be a lm3914 or a lm3915. I have a electrical engineering professor who would help me, but i would have to do most of this research and all i have to do is show him the circuit that i would be building and he would lend me a hand when he had time. The only thing is that i have to put most of it together before i show him.

A colour organ is essentially a very simple spectrum analyzer with 3 or 4 channels instead of 10 or more, and with a simple on/off for each channel instead of a level indication. That said, here is a link to a schematic for a very simple LED VU meter which could easily be modified to drive power transistors which would in turn drive your LEDs: **broken link removed**

And another link, this one for a simple spectrum display. I haven't looked closely at the schematic and the write-up looks like it was automatically translated from Greek or something: **broken link removed**

Do you have links to any of the circuits you have considered which you could post?


Torben
 
Yes, that should work, although I'm unclear on why you want 3 low channels instead of of just one low channel or 3 separate channels for the lows, mids, and highs.



A colour organ is essentially a very simple spectrum analyzer with 3 or 4 channels instead of 10 or more, and with a simple on/off for each channel instead of a level indication. That said, here is a link to a schematic for a very simple LED VU meter which could easily be modified to drive power transistors which would in turn drive your LEDs: **broken link removed**

And another link, this one for a simple spectrum display. I haven't looked closely at the schematic and the write-up looks like it was automatically translated from Greek or something: **broken link removed**

Do you have links to any of the circuits you have considered which you could post?


Torben


I just figured that you needed the three low channels, but if one will work then that is way better. The LED Vu meter would be awesome. It would look a lot cooler than having it just pulse on and off. Now you say i can just use a power transister to power the excess amount of LEDs? What type of original power supply would i need? The VU meter link (the first one) is the one i am planning on building. I have to buy a few lm3915s, but my questions is that since one lm3915 is only capable of handling 10 leds at a time, would i be able to cascade other lm3915s in order to get the amount of LED's i would need to get the effect. I would have to cascade them so that all the LEDs fall into one meter rather than having 5 seperate vu meters(50 Leds, 10 Leds per chip). Also i think the rating on those LEDs were about 11Ma. If thats the case just with 10 Leds i am at 1 Amp. So what kind of DC power supply would i need to power this monster. Would it be easy to expand in LEDs also. 50 might be not enough for what i am going for.
 
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I just figured that you needed the three low channels, but if one will work then that is way better. The LED Vu meter would be awesome. It would look a lot cooler than having it just pulse on and off. Now you say i can just use a power transister to power the excess amount of LEDs? What type of original power supply would i need? I see that you shouldnt use ac, so would i need a transformer to power a 50+ Leds?

Nope--transformers work on AC, not DC. (Well, there will probably be a transformer in whatever power supply you use for the thing, but you should be able to ignore that since it'll probably be inside a wall wart).

When you string LEDs together in series, you have to add their forward voltage drops together to determine what voltage you need to drive them. Their current ratings, however, do not add together when in series. For instance, 20 LEDs rated for 1.7V and 20mA each would require 34 volts and 20mA to drive. Parallel is the opposite: if you put those same 20 LEDs in parallel, you only need 1.7V to drive them all, but the current draw will be 400mA. You'll probably want to split the difference and for each group of 20 LEDs, split them up into a few strings of LEDs. How you split them up will depend on the power supply you have.

The transistors or MOSFETs you use to control the LED strings will also depend on how much power you wind up needing for the LEDs. For this project you won't need anything too beefy.


Torben
 
ok cool, now looking at the IC chips, is it possible to power more than 10 LEDs per one lm3915? I will be drawing up a diagram of the table and where the leds are going to go, as well as a link to a video of something similar as to what i want to accomplish.
 
ok cool, now looking at the IC chips, is it possible to power more than 10 LEDs per one lm3915? I will be drawing up a diagram of the table and where the leds are going to go, as well as a link to a video of something similar as to what i want to accomplish.

There are two things you might mean here--and I think you might actually mean both. ;)

You can drive multiple LEDs per LM3915 output by using transistors to switch them.

You can also create, say, a 20-segment output by daisy-chaining two LM3915s. Check the datasheet: **broken link removed** (scroll down to "Datasheet" and click on the PDF icon labelled "Download"). Hint for future reference: I found this by Googling "lm3915 datasheet"; that works for a lot of components.

The datasheet will tell you more than you ever wanted to know about lm3915s. This datasheet is actually pretty well written to boot and has lots of examples, including several examples of how to daisy-chain multiple LM3915s. Check out the Application Hints starting on page 9.

The diagram of what you hope to build will be very useful. :)


Hope this helps,

Torben
 
Wow that chart is amazing thanks a lot Torben! After reading it does this mean say i have 400 LEDs would i need 40 chips? Because all the schematics show the chips hooked up to ten LEDs each. But your saying with a transistor i could hook up more than 10 leds per chip?
 
Wow that chart is amazing thanks a lot Torben! After reading it does this mean say i have 400 LEDs would i need 40 chips? Because all the schematics show the chips hooked up to ten LEDs each. But your saying with a transistor i could hook up more than 10 leds per chip?

No, you wouldn't need 40 chips. No worries there.

Let's call the outputs OUT1 through OUT10, and I'm also going to assume we're using the bar graph mode and not the dot mode.

With a little signal, the LED on OUT1 lights up. With a little more signal, the LEDs on OUT1 and OUT2 light up. And so on. At full volume, all 10 LEDs light up.

Now, you can either make the display longer (have outputs OUT1 through OUT20, say) by daisy-chaining two LM3915s so you'd have 20 volume levels displayed instead of just 10. Or, you could make the display wider, by using transistors to hang, say, 10 LEDs off OUT1, 10 LEDs off OUT2, etc. Or you could combine the two methods for a "long and wide" display. From what the datasheet says though I'd stick with daisy-chaining two LM3915s at most--the more you daisy-chain them the more sensitive it'll be at the lower end of the range and the more care you'll need to take to make the lower end accurate (if I'm reading the datasheet correctly).

So say you wanted to drive 400 LEDs on one LM3915. You could drive a transistor off of each output to drive 40 LEDs per output. If you're running the LM3915 at 20V and you're using 20mA 1.7V LEDs, you could hook up the 40 LEDs as 4 strings of 10 LEDs and put a 150Ω resistor on each string. I think a 2N2222A transistor would suffice to drive the array. Then repeat that for each LM3915 output. Now, for each signal level you'd see 40 LEDs simultaneously light up instead of just 1.

Note that I'm not an expert on this (hobbyist here) and I have to go out for a few hours but I'll see about working out my assumptions later tonight if someone else doesn't beat me to it first.


Torben
 
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OK, so that looks like they are using eight rows of LEDs with 20 LEDs per row. You can certainly do that with just two LM3915s, as far as I can see. So that's only 160 LEDs for the VU meters. I'll assume a 18VDC supply and 1.7V/11mA regular red LEDs.

Also, my original comments on the transistors was wrong: you'd want PNP transistors such as 2N2907s instead of 2N2222 NPNs.

For this you'd run lines from the LM3915 outputs to the bases of the 2N2907s and connect the 2N2907s' emitters to ground. Each 2N2907 would have a string of 8 LEDs connected to its collector, with their anodes pointing toward the transistor and their cathodes toward ground. The last LED in each string is connected to ground via a 470Ω resistor. If you have, say, 20mA LEDs, use 220Ω resistors instead.

The LM3915's outputs are current regulated, so you want to pick a good drive current for the transistors. You should check out page 9 on the datasheet, as well as Figure 8 in Application Hints.

I have to sleep now but that should get you started. I know you won't need much current on the transistor bases to get the LEDs to light but I'm too tired to work out the values right now. :)


Good luck,

Torben
 
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You'll need to rework some values in what I posted above in order to use these LEDs, but that shouldn't be hard.

Do you have plans for the 340 LEDs not needed by the VU meters?

What is your available choice of power supplies?


Torben
 
I will be keeping the extra leds just incase something happens. I havnt decided on what my choice of power supplies are. I am open to pretty much anything. I am not sure exactly how much power i would need.
 
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I will be keeping the extra leds just incase something happens. I havnt decided on what my choice of power supplies are. I am open to pretty much anything. I am not sure exactly how much power i would need.

OK, well first you need to draw out a diagram and write up a list of what you ultimately want the table to do. Will you have only the VU meters or will there be other lights (logos, washing cups, etc)?


Torben
 
As for the diagram i am still working on it. A list of ultimately what i want the table to do (electronic wise) is just have the VU meter. There will be a couple of other led strips, but i have that under control and those just always stay on. S othe only think i want is the VU meter. Just to clarify, when you say diagram you mean schematic right?
 
As for the diagram i am still working on it. A list of ultimately what i want the table to do (electronic wise) is just have the VU meter. There will be a couple of other led strips, but i have that under control and those just always stay on. S othe only think i want is the VU meter. Just to clarify, when you say diagram you mean schematic right?

Actually, no: I meant like a layout of how everything on the table would look. You'd just pretty much described that. :)


Torben
 
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