Post on 14-Feb-2017
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07-ADC (Analog to Digital Converter).
By : Mohamed Fawzy
Programming AVR Microcontrollers
© Mohamed F.A.B 2015
Lecture Notes:
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o Set Your Phone To Vibration Mode.
o Ask any time.
o During labs, Feel Free To Check Any Materials or
Internet.
o Slides are self content.
o Feel Free To Share This Materials With Your Friends.
o Work Hard For Achieving Most Of This Course.
© Mohamed F.A.B 2015
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Don't Forget !!!!
© Mohamed F.A.B 2015
Any Expert Was Once A Beginner
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Lesson(12).
© Mohamed F.A.B 2015
Lesson (12):
Analogue to Digital Conversion.
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Lesson (12) Topics.
© Mohamed F.A.B 2015
► What and Why ADC.
► Characteristics of ADC.
► Interfacing LM35 temperature sensor.
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What & Why ADC?
© Mohamed F.A.B 2015
Digital Computers uses binary values, but in physical
world everything is analog.
Temperature, Pressure, humidity, and velocity are
examples of physical quantities.
A physical quantity is converted to electrical signals
(voltage or current) using device called sensor.
So, we need Analog-to-Digital Converter to translate
the analog signal to digital numbers so that micro-
controller can read and process them.
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Example.
© Mohamed F.A.B 2015
AnalogD
igita
l
0
1
1
0
0
0
0
1
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Characteristics of ADC.
© Mohamed F.A.B 2015
The resolution of ADC is the number of bits at which
converted data stored in such as 8, 10, 16 or even 24-bit.
Resolution
Vref
It is an input voltage used for voltage reference.
𝑠𝑡𝑒𝑝 𝑠𝑖𝑧𝑒 =[(𝑉𝑟𝑒𝑓+) − (𝑉𝑟𝑒𝑓−)]
2𝐵𝑖𝑡 𝑛𝑜
𝑠𝑡𝑒𝑝 𝑠𝑖𝑧𝑒 =[5 −0 ]
210=
5
1024=0.00488 V*1000=4.88 mv
Higher resolution ADCs means smaller step size and high accuracy.
Smaller Vref ADCs means smaller step size and high accuracy.
NOTES:
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Characteristics of ADC. Cont’
© Mohamed F.A.B 2015
Conversion Time:
Conversion time is the time it takes to convert the
single analogue sample to digital.
o Example.
Digital Output=𝑉_𝐼𝑛𝑝𝑢𝑡
𝑆𝑡𝑒𝑝_𝑆𝑖𝑧𝑒
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ADC Features of ATMEGA32.
© Mohamed F.A.B 2015
10 bit ADC.
It has 8 analog input channels.
Converted output binary data is held by two
registers ADCL and ADCH.
Three options for Vref (VCC or 2.56V or External
AREF pin).
Conversion time is defined by crystal frequency
connected to XTAL pins and ADPS0:2.
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ADC registers in ATMEGA32.
© Mohamed F.A.B 2015
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ADC registers in ATMEGA32. cont’
© Mohamed F.A.B 2015
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ADC registers in ATMEGA32. cont’
© Mohamed F.A.B 2015
• Bit 7 – ADEN : ADC Enable.
• Bit 6 – ADSC :ADC Start Conversion.
• Bit 5 – ADATE :ADC Auto Trigger Enable.
• Bit 4 – ADIF:ADC Interrupt Flag.
• Bit 3 – ADIE:ADC Interrupt Enable.
• Bit 2:0 – ADPS2:0: ADC Prescaler Select Bits.
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ADC conversion time.
© Mohamed F.A.B 2015
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ADC in ATMEGA32.
© Mohamed F.A.B 2015
We need to make digital voltmeter to measure 5 volt power supply.What about 12V or 24V
Exercise (1).
We need to make temperature controller using LM35
Temperature sensor.
Exercise (2).
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Questions:
© Mohamed F.A.B 2015
Thank You All
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mo7amed.fawzy33@gmail.com
01006032792
fawzy.fab@gmail.com
© Mohamed F.A.B 2015