Analog to Digital Data Conversion

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Analog to Digital Data Conversion
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Analog vs. Digital

• Computers use digital information
• Signals are continuous analog waveforms
• Digital information can be encoded in the analog
  signal

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Modulation

• Digital information coded on a high frequency
  carrier signal
• AM -Amplitude Modulation
• FM Frequency Modulation
• PM Phase Modulation

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Digital Information

• BIT BINARY DIGIT
• either 1 or 0, high or low, yes or no
• Decimal Base of 10

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Base of 10
2543 1000 100 10 1 103 102
101 100 2 5 4 3
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Binary - Base of 2
41 32 16 8 4 2 1 25 24 23
22 21 20 1 0 1 0 0 1
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Bits Bytes

• Bit Binary Digit
• Byte 8 Bits, 28 or 256 combinations
• 1 Kilobyte (KB) 210 1024 bytes
• 1 Megabyte (MB) 220 1,048,576 bytes
• 1 Gigabyte (GB) 230 1,073,741,824 bytes
• 1 Terabyte (TB) 240 1,099,511,627,776 bytes

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Components for A/D Conversion

• Measurable Quantity
• Measurement Device
• Analog Signal
• Transducers
• transforms one form of energy to another form
• Electrodes
• sense biological signals

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Components for A/D Conversion

• Analog Conditioning
• Electronic circuitry to modify the signal before
  it enters the computer for digitization.
• amplification
• filtering
• integration

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Components for A/D Conversion

• A/D Conversion board software
• Necessary to digitize the analog signal
• Sample the analog signal at a set frequency and
  store it as binary information

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Functions of A/D Board

• Sampling
• Analog signal is sampled by switching at a set
  frequency
• Nyquist rule at least twice frequency of signal
  to avoid aliasing

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Signal Alias (sampling frequency too low)
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Functions of A/D Board
Quantitization Number of levels of voltage
determined by the number of bits in
conversion The number of bits used to represent
each conversion effects how many possible
different values can be resolved from the
converter... of Bits Possible of
Values 1 2 2 4 8 256 12 4
096 Encoding Assigning a digital code
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Resolution

• Resolution of an A/D converter
• A measure of the smallest amplitude value as a
  percent of full scale to which a quantity can be
  determined

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Voltage Range Common ranges are -10v to
10v, -1v to 1v, -100mv to 100mv
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Resolution Calculation 12 bit converter, -10v
to 10v -10v to 10v 20 v 12 bit resolution
4096 possible values 20v / 4096 0.00488v per
bit (4.88 mv per bit)
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A/D Software

• Require A/D board compatible control software
• LABVIEW
• LABoratory Virtual Instrument Engineering
  Workbench
• MATLAB