Objective
To get familiar with Digital to Analog conversion
Tools
Proteus, MPLAB Compiler.
Theory
In digital systems data can be processed only if it’s represented in Digital format (0,1)
while the majority of real world applications requires Analog signals. This leads to the
need for conversion between analog and digital formats. For example, most modern audio
signals are stored in digital form (for example MP3s and CDs) and in order to be heard
through speakers they must be converted into an analog signal. Digital to Analog
Converters are therefore found in CD players, digital music players, and PC sound cards.
Digital to Analog Converter
In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a
digital (usually binary) code to an analog signal (current, voltage or electric charge).
Digital-to-analog converters are interfaces between the abstract digital world and analog
real life. Usually, DACs are used to convert 8-bit digital data into analog signal. If a
greater precision is needed, chips with 12 bit, 14 bit, or 16 bit data convertibility are
available.
Almost all the DACs enable the user of the chip to define the high and low references of
the analog output provided that these references fall within a fixed range defined for that
chip.
Let’s assume that we have a 3-bit DAC that has three digital lines (D2, D1, D0) and has
one output analog line. Assume that we assign the references of the analog output to:
Vref-=0 V and Vref+=1 V, then the input/output relation will be as shown in the table
From the table we can derive the following points:
The 3-bit DAC has 23=8 possible combinations. If a converter has n input lines it can
have 2n input combinations.
If the low and high references of the analog output is V1 to V2 , then the change in the
output corresponding to each increment of the (n-bit) digital input is
This value is defined as a resolution. In our example the resolution is (1-0)/23=1/8 V
When the MSB (D2) is 1 and the other bits are zeros, the output analog is half of the
full scale. In our example, the input (100) leads to ½ V analog output.
For the maximum input (all ones), the output is equal to the value of the full scale
minus the value of the resolution. In our example, the maximum digital input (111) leads
to the output: 7/8.
DAC0800 Chip
DAC0800 is a simple 8-bit Digital to Analog converter with no buffering of inputs. It has
the following features:
Fast conversion time (100 ns)
High output compliance(-10 V to +18 V)
Complementary current outputs
Wide power supply range
Interface directly with TTL, CMOS, PMOS and others
Wide power supply range ( ±4.5V to ±18V )
Low power consumption
Low cost
Lab 10
Lab Exercises
Part1
Connect the circuit as shown in the figure.
Notice that we drive the Chip with a power of 5V so we've connected V+ to +5 and V- to
-5. However you can drive the chip with any voltage within the range (±4.5V to ±18V).
Change the state of the input switches to find the corresponding voltage by taking the
voltmeter reading.
Notice that we connect Vref- to 0 and Vref+ to 5V this means the range for the analog
output will be within the range 0V to +5V
Analyze the results.
Lab 10
Part 2
Connect the circuit shown in the Figure below on Proteus ISIS program.
Write an assembly program for the PIC18F4550 chip that changes the digital value on
PORTD periodically and observe how the speed of rotation of the DC Motor will vary
accordingly.
Part 3
Write a basic program that do the same as program in part2