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Author Topic: Bass activated LED's  (Read 7621 times)

linear

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Re: Bass activated LED's
« Reply #10 on: September 14, 2005, 09:35:41 AM »

That's probably the wisest approach. The impedance of the meter is reasonably high, but not high enough that I'd want it upstream from my amplifier in the signal chain. Make sure the trimmers you use at the input are rated for some reasonable power.
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trials_modder

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Re: Bass activated LED's
« Reply #11 on: February 13, 2006, 03:18:17 PM »

I didnt quite understand the instructions to make a low-pass filter from those links. Can anyone clarify/draw a breadboard diagram (like the Stereo VU meter's instructions)? Thanks.
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viridius

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Re: Bass activated LED's
« Reply #12 on: February 13, 2006, 04:06:29 PM »

Ok, well take a look at Linear's link, specifically the "active low pass filter" part.  There are two parts to the circuit: an RC filter and an opamp buffer stage.  If you feed a signal with different frequencies into the RC filter, it will pass low frequencies up to the frequency determined by R and C at which point the output will begin to drop as frequency increases.  Now, if you were to feed the output of the RC filter directly into the chip itself, you'd find that the rolloff frequency would be affected.  That's where the opamp comes in.  The input impedance of the opamp is too high to significantly affect the rolloff frequency of the RC filter, so you get the desired performance.  If you want, you can set the opamp to increase the amplitude of the signal with resistors R1 and R2 or if you don't want gain, you can omit them altogether and connect the output of the opamp straight back to the inverting input (the - sign on the opamp).  The output of the opamp can now drive the chip.
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trials_modder

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Re: Bass activated LED's
« Reply #13 on: February 13, 2006, 05:05:34 PM »

Wow, thanks for the great explanation, but I am still confused as to build one of these. I'd ideally like the output strength to be the same as the input strength, just with more bass and less of everything else.
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viridius

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Re: Bass activated LED's
« Reply #14 on: February 13, 2006, 07:53:22 PM »


R1 and C1 you should choose for yourself according to the equation f = 1/(2*pi*R*C) with f in Hz, R in ohms, and C in farads.  The filter has a gain of 0dB at 0Hz, decreases to -3dB at frequency f, and rolls off at -20dB/decade after that.  Leave pins 1, 5, and 8 unconnected  You'll only get half the output signal because you're running off of a single ended supply, but I doubt you'll notice anything.
« Last Edit: February 13, 2006, 08:03:14 PM by viridius »
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trials_modder

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Re: Bass activated LED's
« Reply #15 on: February 14, 2006, 02:44:44 AM »

Right, it is starting to make more sense, except that there is only one line for each input/output when the wires from a mono headphone jack have two. I'm guessing the easiest way for that  f = 1/(2*pi*R*C) equation is to set f to say 30, then put in 10 microfarads for C as i have that capacitor readily available, then find the necessary R to put in.
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viridius

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Re: Bass activated LED's
« Reply #16 on: February 14, 2006, 03:13:04 AM »

30 Hz is a little low.  I suggest a 1uF capacitor with an 820 ohm resistor for a cutoff frequency of 194 Hz.  And yes, you will need to make two circuits, one for each channel.  You could look into the 1458, which has two 741 opamps in the same 8-DIP package.
« Last Edit: February 14, 2006, 03:15:37 AM by viridius »
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trials_modder

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Re: Bass activated LED's
« Reply #17 on: February 14, 2006, 12:19:12 PM »

How would the schematic for that look??
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glassx

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Re: Bass activated LED's
« Reply #18 on: February 14, 2006, 12:28:57 PM »

Oh wow i knew i made this thread for a reson! It took 5 months but I'm gunna do it! w00t. Getting materials tonight.
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viridius

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Re: Bass activated LED's
« Reply #19 on: February 14, 2006, 02:47:14 PM »

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