# 5x10 vu meter

Posted on Feb 6, 2014

A nice schematic for an lm3915 VU meter. I have attempted to create a band pass filter in order to only input part of the audio frequency spectrum into the VU meter circuit, this is becuase I plan to have 5 of these circuits to make a spectrum analyser or w/e its called. I have not been able to work out the value for the capacitor marked C2 in the diagram because I

dont know what resistance the lm3915 circuit will produce and therefore I cannot use the formula of 1/(2piRC) = cuttoff frequency. Also note that I may well be in slightly over my head with this since I have not touched electronics since about two and a half years ago when I did electronics GCSE. I will attach the schematic of the spec analyzer I designed and built for my stereo. You can use the filter section values. Each one is a bandpass filter centered on the frequency listed by it. The filters are shown on the page 2 schematic below. I believe on page 1, I have the explanation and formulas for calculating the frequency for the bandpass center frequency (Fo). Also "Ao" is the midband gain of the filter. So if I wanted to split it into 5 bands i would just use filters with Fo of 62, 250, 1K, 4K and 16K. But how do I make the bands wider so that I am not missing chunks of the spectrum Or is that where the midband gain comes into it These are not unity gain filters, they have voltage gain. take the 1K Hz filter: midband gain means if you put a 10mV (1 KHz) sine wave into it, you will get out a 1Khz sine wave whose amplitude is larger by the midband gain. So if I wanted to split it into 5 bands i would just use filters with Fo of 62, 250, 1K, 4K and 16K. But how do I make the bands wider so that I am not missing chunks of the spectrum Or is that where the midband gain comes into it Well I dont really know the difference so...

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