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Sallen Key Low Pass Filter, bandpass filter

Maglatron

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I'm a total novice when it comes to this, I'm designing a Spectrum Analiser 20 columns wide and 30 rows up and have worked out a small portion with the use of LM3914 to represent a column, I need to know how to activate the band thats lighting up and how to filter from the left 32Hz to the right side of 16000kHz evenly spaced along the 20 columns I need bandpass filters op amps and peak detectors and have been put onto the sallen key filter to help with part of it. I,m uploading the first column as an .asc file! thanks for looking.
 

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  • lm3914 column.asc
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Maglatron

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So I've come up with an Idea, if someone can tell me how to make a filter for say the 32Hz band and make it step by step, so that I can follow it like instructions or a template, then I can do the same process for the other 19 bands!
 

Harald Kapp

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You may try this filter design wizard.
Besides that one you can easily find heaps of materila on how to design analog filters on the internet.
 

Maglatron

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Thank you hararld kapp. Should I be looking at high pass filters or low pass filters or even bandpass filter? that site seems incredible by the way
Ok I'm going bandpass!
 
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Maglatron

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ok is anybody available to talk me through the process on the site for example 32Hz range please?
 

Maglatron

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ok I've followed a video and I get to this point I don't understand what the graph shows, what dB is or why at 20kHz it's equal to 1dB from 4dB I need a bit of a nudge and a clear explaination of whats going on here I understand that this is a low pass filter
 

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  • first low pass.jpg
    first low pass.jpg
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bertus

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Hello,

Have a look at the attached PDF's for filter design.

Bertus
 

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  • sloa049b_Active Low-Pass Filter Design.pdf
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  • sloa093_Filter Design in Thirty Seconds.pdf
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Maglatron

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thanks I'm uploading what I have done today, the low pass filter when it reaches 20kHz the decibels go to 1 dB and the high pass filter when it reaches 20Hz the decibels go to one again, I think this is significant why do we try to aim for 1 dB
 

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  • LOW PASS plus HIGH PASS FILTER2.asc
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Maglatron

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ok so from the filter design in thirty seconds I think what I need is the "Figure 3. Narrow (Single Frequency) Band Pass" confirm if correct
 

Maglatron

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Ok so I now want to know what does E-12, E24, E96 mean from the filter design in thirty seconds pdf because it says "(pick a standard value from Appendix A)." in section 4 Narrow (Single Frequency) Band Pass Filter, many thanks
 

Maglatron

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cool, is it a question of precision? fro what I understand E96 has 1% tolerance and are for precision electronics, is this true?
 
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Maglatron

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What is a decade? "This process is followed through for all the values in a decade," and also, just to make sure, are the capacitor standard values the same digits as the resistors
 

Maglatron

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E-24 Resistor / Capacitor Values
1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5,
8.2, and 9.1; multiplied by the decade value.
Might sound silly but I have to check what is meant by "multiplied by the decade value."?
can you do me a couple of examples please?
 

Maglatron

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Next question what qualifies for low frequency and high frequency? cheers!
 

Maglatron

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Ok back to basics how do gain in decibels relate the the Narrow (Single Frequency) Band Pass. how do I decide how many dB (how much gain) or change in amplitude and why? Say I picked an arbitrary number, change amplitude by 10, the gain in dB is equal to 20dB, I bought an online electronics course and it derived the all the numbers so I understand how to reach them through formula but I shall rely on the dB-power-amplitude ratio chart, So now the question is that say the frequency is filtered and the dB gain of 20 how do I link it to the LM3914 and the LED's and how steeply would the how tight would the frequency filter tolerance's be?
 

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  • decibel power amplitude ratio.jpg
    decibel power amplitude ratio.jpg
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Maglatron

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so I have a question if:
p1 = 10dBm
p2 = 5dBm can you talk me through how to add them please!?
 
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