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Lm3915 Help

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cLuBsTa

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Hey everyone, my 1st post.

Im trying to make a led vu meter using the lm3915 IC. ive built 2 of them using circuits from 2 different websites. They work, but not as good as i hoped they would. I have nothing connected to pin 9 yet all the leds seem to light up, I.E. like it is in bar mode (not Dot mode). also it is not very responsive to the music, usualy all leds up to around 7 and 8 turn on. I have tryed using audio from my xbox, discman and my PC.

So the problem is - Bar mode when it should be in dot mode and is also not very responsive to music. Have tried rock, rap and techno.

Anyone know what might be wrong with it ?
 
With pin 9 not connected (floating),it should be in dot mode
Can you post your circuit or a link to one that you built.
 
Difficult to say without seeing the circuit, but consider:

The dot mode problem is strange, the data sheet for the LM3915 just says leave pin 9 o/c for dot mode, you have done that and yet you get bar mode.
You have built two different circuits, and had similar results both times I assume?
Could it be that there is something wrong with your power supply, construction technique, faulty component(s)?

As far as the top 2/3 leds not illuminating, what output are you using to drive this circuit, are you sure there is enough output the drive all the leds?

I dont think that the circuit can distinguish between different kinds on music. :D

JimB
 
Post the circuit! Then we cod tell you what to change.

Try to lower the input AC filter cap
Make shure the powersuply isent noisy (put an 1000uF cap in paralel whith the power suply)


If its on a breedbord try to put an pulldown resistor on the 9 pin (its a problem whith the reset pin on 555 timers too wen there on a breadbord)
 
LED VU Meters also work Considerably better if you Rectify the Signal with a Peak detector, Before putting it into the LM3915.

If you have More than One LED Lighting in the DOT Mode, You have Parastatic Oscillations. You may need a better Layout or A Supply Bypass Capacitor. Ground Loops can be a Problem Also. All grounds on the LM3915 should come to a Single Point Ground. Not A Common Bus Ground.

Need more help, Email Me.
 
Thanks for all the replys. I got my circuit diagram from www.gideontech.com. The other circuit i have no idea where it is from, i dont have a picture of it on my computer as i printed it out and deleted it.

I dont beleive it is my power supply as i have tried the 12 volt from my pc, and a 12 volt Transformer.

Yes Pin 9 is disconnected from everything and yet it displays in bar graph. Sometimes the top Led's will light up, but instead of the display moving heaps. it just sits around leds 6,7,8. It dosnt look very nice, I thought this IC would have the all leds moving heaps.

If Anyone else has done this circuit could you please post a photo of it.

Edit: Resized Picture.
 

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:shock: That poor IC.

with chemelec's advice, you'd want to connect the ground of the resistor (grey wire on left of pic) to pin 2 of the IC, so you only have one ground coming off of the IC.

Do you have any sort of cap. on the audio input?

this is the schematic that I use
**broken link removed**
works great too.

oh yeah, you have to be sure not to get the IC too hot when you are soldering to it, I'm not sure of the exact soldering time, but you cant keep the soldering iron on there for very long.
 
Ok i will try that now. I have played around with using a capisitor but no luck. I also read that the maximum time that you can apply the soldering iron for is under 2 seconds i think.
 
wow it works, very responsive now. But It is still displaying in bar mode with nothing conected to Pin 9. Anyone have any ideas?

Also thanks everyone for the quick replys and helpful information.
 
I've always had a problem getting the dot mode to work. I think it was very hard to see the dot.
 
cLuBsTa said:
wow it works, very responsive now. But It is still displaying in bar mode with nothing conected to Pin 9. Anyone have any ideas?

Also thanks everyone for the quick replys and helpful information.

If you've got it wired as the picture above I would have thought it's got a good chance of being unstable, it could well be oscillating - you should'nt wire things with long wires!.
 
I think the circuit is now working as expected.
You are feeding it with an AC signal, the instantaneous voltage will be constantly varying which is why your eyes see a bar display, if your eyes were fast enough you would see a dot display.
As chemelec suggested, you need to rectify the signal before applying it to the LM3915.
Have a look at the LM3915 data sheet. (Google LM3915).

JimB
 
Ok i guess this is how it is suppose to be then. Not very dotty but oh well lol. I have put positive power on pin 9 and it makes the led's glow more brightly.

Thanks Everyone for your help
 
I have to more lm3915 left. Could someone please give me some tips on making it work the 1st time.

I have included a rough image of what i might transfer to a pcb.

Can anyone see anything wrong with this circuit.
 

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For such a simple circuit, I'd recommend just using some perforated board (has a grid of holes drilled 0.1" apart, the same spacing as the pins on the IC). Then just solder wires to the leads.

Unless you are planning on getting into making various circuit boards, then I'd suggest going the printed circuit board route. Materials can get kinda costly.
 
I would suspect your getting Leakage to Pin 9 from the adjoining pins, possibly through the Solder Flux.

Put a 1K Resistor between pin 9 and Ground Pin 2. This should give you a Good Moving Dot Mode.
 
The LM3915's datasheet says that with audio applied directly to its input, many LEDs will respond to instantaneous levels of the audio and each one will be very dim. It also shows a simple low-threshold voltage peak detector circuit that uses a capacitor to briefly hold the level so that a dot stays lighted long enough to see it.
 

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jrz126 said:
:shock: That poor IC.

with chemelec's advice, you'd want to connect the ground of the resistor (grey wire on left of pic) to pin 2 of the IC, so you only have one ground coming off of the IC.

Do you have any sort of cap. on the audio input?

this is the schematic that I use
**broken link removed**
works great too.

oh yeah, you have to be sure not to get the IC too hot when you are soldering to it, I'm not sure of the exact soldering time, but you cant keep the soldering iron on there for very long.
I don't see the need for the PNP in order to drive several LEDs in series, unless you want more current than the LM3915 can deliver.
 
Ok back with a pcb proto type board, fits the IC nicely. Could someone do up a quick schematic using the diagram below for a vu meter.

Were there is white lines, that is where traces are on the opposite side.

I will be running wire to leds so dont put leds on the board.
 

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Here Is what i did real quick in paint. The Green dots indicate a connection.
 

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