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LM3915 Help...

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Ba!nesy

New Member
Hey guys, new to the forums, first post actually.

Recently i've been getting interested in LED's and the like, went on google one day, seeing how some people used LED's and frosted plastic to create lights... came away a few hours later with a list of things that I wanna do haha.

One of these things, include making a VU meter using a LM3915 IC. I didn't get around to buying the components for it, but my brother did for himself. He used a breadboard to try and make the VU meter exactly like its shown in the LM3915 circuit diagram... well not exactly.

1: There is not capacitor (says its needed if cables runing to LED's are more than 6")
2: he attempted this at night, and didn't have the correct resistors, so he used 8 x 1k resistors (he said as best he could tell thay were 1k I've made the mistake of not double checking them) to replace the 8.06k resistor. Also now just looking at it he's only got 1 1k resistor to replace the 2.26k resistor in the diagram. (I know its atleast a 2k resistor, but not 100% on its real figure according to the schematic)
3: input source... well I just don't know much about that.

I dont need the capacitor, but can the 8 single resistors replace the 1 8.06k resistor (please forgive my noobness relating to electronics) or is that just a bog no-no?
Is there anything wrong with the schematic as is? I've read some posts with people having problems with this LM3915.
Any help would be greatly appreciated.
Thanks
Ba!nesy
 

ericgibbs

Well-Known Member
Most Helpful Member
hi Ba!nesy
Please post the circuit diagram or a link to it.
 

audioguru

Well-Known Member
Most Helpful Member
The circuit is the first schematic on the datasheet. It is designed for an input source voltage that has peaks to 9.4V like the output of a power amplifier (5.5W into 8 ohms). Only 2 or 3 LEDs will light if it is fed from an MP3 player. Its resistors can be changed so most LEDs will light during loud sounds from an MP3 player.

Since your brother used the wrong value resistors, didn't bother measuring the input signal level and didn't bother calculating the required resistor values then it probably will not work.

The datasheet for the LM3915 tells exactly how to use it. People who have trouble with it didn't read the datasheet.
 
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