E-626-A Real-Time Embedded Systems (RTES) …bu.edu.eg/portal/uploads/Engineering, Shoubra/Electrical...Lecture #8 Data acquisition and manipulation ADC & DAC Instructor: Dr. Ahmad

Lecture #8 Data acquisition and manipulation ADC & DAC Instructor: Dr. Ahmad El-Banna

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E-626-A Real-Time Embedded Systems (RTES)

Integrated Technical Education Cluster At AlAmeeria‎

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Agenda

Digital, Analog signals & Acquisition

ADC

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Analog and digital quantities

• Most transducers produce output signals that are an analog of the quantity they represent.

• For example: Temperature sensors & microphones.

• Analog signals are fine things, but they suffer from a number of big disadvantages.

• Digital signals, on the other hand, perform better on most counts and with today’s technology are easier to work with.

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Some properties of analog and digital quantities

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The data acquisition system

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• Elements of a (four-channel) data acquisition system

ADC ch/s

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• The ideal analog-to-digital converter input/output characteristic

• Sample & Hold Circuit

Typical timing requirement of one analog-to-digital conversion

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The PIC 16F87XA ADC module

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Controlling the ADC

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• The ADC is controlled by two SFRs, ADCON0 and ADCON1). • The result of the conversion is placed in two further SFRs,

ADRESH and ADRESL.

The ADCON0 register (address 1F H )

The ADCON1 register (address 9F H )

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Formatting the analog-to-digital converter conversion result

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• Calculating acquisition time

DAC

• The reverse function of ADC.

• Needs external interface circuit.

• Convert digital values into continuous analogue signal

• Decoding digital value to an analogue value at discrete moments in time based on value within register

Where E0 is output voltage; Eref is reference voltage; Bn is status of successive bits in the binary register

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Examples of DAC Circuits

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• Scaling Adder as a four-digit DAC

• An R/2R ladder DAC

I0=+V/8R I1=+V/4R I2=+V/2R I3=+V/R

Vout(D0)=-Rf I0

Vout(D1)=-Rf I1

Vout(D2)=-Rf I2

Vout(D3)=-Rf I3

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Sample Project

• Design and implement a digital voltmeter.

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• For more details, refer to:

• Chapter 11, T. Wilmishurst, Designing Embedded Systems with PIC Microcontrollers, 2010.

• The lecture is available online at:

• http://bu.edu.eg/staff/ahmad.elbanna-courses/12134

• For inquires, send to:

• [email protected]

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