3KHz
LOW PASS FILTER PLUS AUDIO AMP
This circuit uses a switched capacitor filter IC from National
Semiconductor to filter signals with frequencies higher than the 3KHz
needed for voice audio. The schematic includes an audio amplifier that
is designed to drive a standard audio head phone. The circuit is
described in more detail in the receiver section
of Dave Johnson's
Handbook of
Optical Through the Air Communications.
(this link is off-site) |
AUDIO
AMP + 3KHz FILTER
This circuit is the audio amp section for a complete optical
transmitter. The circuit amplifies and filters the voice audio signals
from an electrets microphone. The circuit is described in more detail in
the transmitter circuit section of Dave
Johnson's
Handbook of Optical Through the Air Communications. (this
link is off-site) |
ELECTRIC FIELD DISTURBANCE MONITOR
This schematic is the power supply and front-end sections of the field
monitor that is discussed in more detail at
Electric
Field Disturbance Monitor. The system can detect human and animal
motion by the electric fields they disturb. |
LOW PASS
ACTIVE FILTER DESIGN COLLECTION
This is a collection of inverting and non-inverting active low pass
filter circuits. I included one, two, three, four and six pole filter
circuits. You can change the component value ratios shown, to achieve
any frequency cut-off you may need. The circuit does not specify an
operational amplifier. The circuits should be used to select the needed
resistor and capacitor components for a particular frequency knee and
roll-off slope. |
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Active 2nd Order Filters: |
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Active Filter has Wideband Tuning Range: EDN-Design Ideas
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Adjustable Filter Provides Lowpass Response: EDN-Design Ideas PDF
contains multiple circuits - scroll to find the one of interest |
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Basic
Introduction to Filters: application notes on active, passive and
switched capacitor filters, document in PDF format |
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Butterworth Filters: |
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Chebyshe
Volt / Butterworth Filters: |
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Chebyshe Volt Bandpass Filter: |
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DC
Accurate, Active RC Lowpass Filter: |
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Low Pass Active Filter: |
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Lowpass filter discriminates step input from noise : EDN-Design
Ideas / Numerous applications exist in industry, particularly with
control systems, in which it is desirable to remove all but the lowest
frequency components from a signal to effectively yield a dc voltage.
This voltage may, for example, serve as a setpoint to a PID controller
in a process-control or an HVAC application, in which the cable that is
carrying the analog signal is exposed to a wide spectr......
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Lowpass filter uses only two values: EDN - Design Ideas / In recent
years, image-parameter design of LC filters has received new
consideration (references 1 and 2). The composite lowpass filter uses
interior constant-k full sections terminated by m-derived half-sections.
For best passband response, you usually select m to equal 0.6. However,
m=0.5 can still give useful filter performance while reducing the number
of component values.. |
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Single resistor tunes lowpass filter : EDN-Design Ideas / Any
tunable, second-order, active RC-filter section requires at least two
thoroughly matched variable resistors. But the lowpass implementation in
Figure 1 provides for wide-range cutoff-frequency control using only a
single variable resistor, R. In addition to the resistor, this filter
comprises an operational amplifier, IC2, which serves as a unity-gain
buffer; two capacitors, C1 and C2; ...... |
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Single Supply Twin T Butterworth Low Pass Filter:
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