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
• American Standard Code for Information
  Interchange (ASCII)
• eg A 01000001, 00100110
• 1 Kilobyte (KB) 210 1024 bytes
• 1 Megabyte (MB) 220 1,048,576 bytes
• 1 Gigabyte (GB) 230 1,073,741,824 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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Sample Hold Device

• Signal memory device that can store a voltage for
  periods of time ranging from microseconds to hours

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Components for A/D Conversion

• Analog Conditioning
• Electronic circuitry to modify the signal
• amplification
• filtering
• integration

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Components for A/D Conversion

• A/D Conversion board software

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Functions of A/D Board

• Sampling
• 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