07 Analogue to Digital Converter(ADC).2016

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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.


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Don't Forget !!!!


Any Expert Was Once A Beginner

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Lesson(12).


Lesson (12):

Analogue to Digital Conversion.

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Lesson (12) Topics.


► What and Why ADC.

► Characteristics of ADC.

► Interfacing LM35 temperature sensor.

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What & Why ADC?


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.


AnalogD

igita

l

0

1

1

0

0

0

0

1

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Characteristics of ADC.


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’


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.


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.


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ADC registers in ATMEGA32. cont’


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ADC registers in ATMEGA32. cont’


• 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.


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ADC in ATMEGA32.


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:


Thank You All

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07 Analogue to Digital Converter(ADC).2016

Engineering

Transcript of 07 Analogue to Digital Converter(ADC).2016