Help designing analog filter designs for an audio activated 8x8x8 LED cube
Help designing analog filter designs for an audio activated 8x8x8 LED cube
(OP)
I am working on designing a music visualization system using LEDs. I would like to create an analog design that uses op amps to filter, amplify, and add DC bias to an audio signal so it can be read into the A/D of a 5V microprocessor. The input signal is a +/- 1.5V volt audio signal coming from an MP3 player. From this signal I need to produce three output signals. This means that I need to design three filters (a lowpass, a bandpass, and a highpass). These filters also need to amplify and bias the input signal so it will be a 0 to 5V signal that can be read by the processor's A/D at the maximum resolution. So basically what I have pictured is to first bias the signal, then amplify it, then filter it:
MP3 Player Audio signal --> Bias --> Amplify --> Filter --> uP
I am familiar with building filters with amplification, but I am not sure about the correct way to go about adding a DC bias to the filters with amplification.
Lowpass (bass range): cutoff f @ ~500 Hz
Bandpass (mid range): center f @ ~2250 Hz
Highpass (high range): cutoff f @ ~4kHz
The parts I have available for use are: LT1632 dual op-amps, resistors, 100nF capacitors
Measuring the output signal from the iPhone: V(peak-to-peak): ~2.85V centered around 0V
Required Gain: ~1.75
Available Power supply units: +5V and +12V DC
I've tried designing these filters by hand, and using TI's FilterPro software, however I have not been able to achieve the DC bias affect. I have been simulating the filters using LTSpice. I have the design files for the three filters though if it would help in describing my current problem. Any help in this area would be greatly appreciated.
MP3 Player Audio signal --> Bias --> Amplify --> Filter --> uP
I am familiar with building filters with amplification, but I am not sure about the correct way to go about adding a DC bias to the filters with amplification.
Lowpass (bass range): cutoff f @ ~500 Hz
Bandpass (mid range): center f @ ~2250 Hz
Highpass (high range): cutoff f @ ~4kHz
The parts I have available for use are: LT1632 dual op-amps, resistors, 100nF capacitors
Measuring the output signal from the iPhone: V(peak-to-peak): ~2.85V centered around 0V
Required Gain: ~1.75
Available Power supply units: +5V and +12V DC
I've tried designing these filters by hand, and using TI's FilterPro software, however I have not been able to achieve the DC bias affect. I have been simulating the filters using LTSpice. I have the design files for the three filters though if it would help in describing my current problem. Any help in this area would be greatly appreciated.





RE: Help designing analog filter designs for an audio activated 8x8x8 LED cube
As for DC bias, that cannot come from a filter; you need a separate thing like a summing amp.
TTFN
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RE: Help designing analog filter designs for an audio activated 8x8x8 LED cube
Here is the schematic of my low-pass filter which is off-phase and not properly amplified. Also there is a little bit of noise:
Schematic
AC analysis
DC transient response
Any suggestions on how to get rid of the noise and bring the output in phase with the input signal?
RE: Help designing analog filter designs for an audio activated 8x8x8 LED cube
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Help designing analog filter designs for an audio activated 8x8x8 LED cube
RE: Help designing analog filter designs for an audio activated 8x8x8 LED cube
http://www.ti.com/lit/an/slod006b/slod006b.pdf
RE: Help designing analog filter designs for an audio activated 8x8x8 LED cube
RE: Help designing analog filter designs for an audio activated 8x8x8 LED cube
Other random hints:
You can often employ a little audio transformer if you need to increase voltage into an input with reasonably high input Z. But if your peak is only a single bit away from full scale, then don't bother. It's call headroom.
Biasing an input requires at most a capacitor and two resistors.
Assuming the processor has any processing horsepower at all, everything else can be done in software. Combined with the above hints, there's no need for any opamps at all... ...Not a good approach if this is in support of a class about opamps.
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