Daqarta
Data AcQuisition And Real-Time Analysis
Scope - Spectrum - Spectrogram - Signal Generator
Software for Windows
Science with your Sound Card!
The following is from the Daqarta Help system:

Features:

Oscilloscope

Spectrum Analyzer

8-Channel
Signal Generator

(Absolutely FREE!)

Spectrogram

Pitch Tracker

Pitch-to-MIDI

DaqMusiq Generator
(Free Music... Forever!)

Engine Simulator

LCR Meter

Remote Operation

DC Measurements

True RMS Voltmeter

Sound Level Meter

Frequency Counter
    Period
    Event
    Spectral Event

    Temperature
    Pressure
    MHz Frequencies

Data Logger

Waveform Averager

Histogram

Post-Stimulus Time
Histogram (PSTH)

THD Meter

IMD Meter

Precision Phase Meter

Pulse Meter

Macro System

Multi-Trace Arrays

Trigger Controls

Auto-Calibration

Spectral Peak Track

Spectrum Limit Testing

Direct-to-Disk Recording

Accessibility

Applications:

Frequency response

Distortion measurement

Speech and music

Microphone calibration

Loudspeaker test

Auditory phenomena

Musical instrument tuning

Animal sound

Evoked potentials

Rotating machinery

Automotive

Product test

Contact us about
your application!

Voltage Dividers

A simple 2-resistor voltage divider can function as a fixed attenuator to reduce a signal level that is too large.

Given the input voltage Vi and the two resistors R1 and R2, the output voltage Vo is:

Vo = Vi * R2 / (R1 + R2)


The fractional voltage reduction K is:

K = Vo / Vi = R2 / (R1 + R2)


To get a specified output voltage from a known input voltage, pick one of the resistor values and solve for the other:

R2 = Vo * R1 / (Vi - Vo)

R1 = R2 * (Vi - Vo) / Vo


Or, if you know the desired fraction K and want to find the resistors:

R2 = K * R1 / (1 - K)

R1 = R2 * (1 - K) / K


The ratio of the two resistors needed for a given reduction is:

R2/R1 = K / (1 - K)

R2/R1 = Vo / (Vi - Vo)


To determine the input voltage that produces a given output voltage from a known divider:

Vi = Vo * (R1 + R2) / R2


The reduction ratio K is normally used for range changes, such as 0.10 for a 10-to-1 reduction. However, for audio work you may want to obtain a specific reduction in dB. (See dB From Voltages and Working With dB.)

The dB corresponding to a given voltage ratio is:

dB = 20 * log10(Vo / Vi)

dB = 20 * log10(K)

where log is the base-10 (common) logarithm. For voltage dividers, note that K is always less than 1, so the dB value will always be negative.

To find the ratio K corresponding to a given dB value, use the following formula. Remember to use a negative value for dB:

K = 10^(dB/20)

Typical dB values and corresponding voltage ratios:

-1 = 0.891251
-2 = 0.794328
-3 = 0.707946
-6 = 0.501187
-10 = 0.316228
-20 = 0.100000
-30 = 0.031623
-40 = 0.010000
-60 = 0.001000
-80 = 0.000100
-100 = 0.000010
-120 = 0.000001
GO:

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