Ppt

1. ADVANCED ELECTRONICS
ADC and DAC interfacing with 8051
Presentation
By
SATISH KUMAR
Department of Physics
INDIAN INSTITUTE OF TECHNOLOGY MADRAS, CHENNAI 600036

2. INTERFACING TO ADC AND SENSORS
 ADCs (analog-to-digital converters) are among the most
widely used devices for data acquisition
 A physical quantity, like temperature, pressure, humidity, and
velocity, etc., is converted to electrical (voltage, current)
signals using a device called a transducer, or sensor
 We need an analog-to-digital converter to translate the analog
signals to digital numbers, so microcontroller can read them

3. ADC804 IC is an analog-to-digital converter
• It works with +5 volts and has a resolution of 8 bits
• Conversion time is another major factor in judging an
ADC
 Conversion time is defined as the time it takes the
ADC to convert the analog input to a digital (binary)
number
 In ADC804 conversion time varies depending on
the clocking signals applied to CLK R and CLK IN pins,
but it cannot be faster than 110 ms

4. Testing ADC0804

5. Resolution:
The resolution of an ADC is how accurately it will sample
(convert) the analog signals into digital values (i.e. 0s and
1s). Higher is the resolution then greater will be the
accuracy.
Step size:
It is the minimum voltage change that measures by the
ADC. In other words you can say that the step size is the
voltage difference between one digital level (i.e. 0001) and
the next digital level (i.e. 0010 or 0000). For example, If a
4bit ADC has the step size 1 volt then if we will give the 1
volt as input the output will be 0001.
CS: Chip Select
It is an active low pin and is used to activate ADC0804

6. RD: Read Pin
It is an input pin and active at low. ADC stores the result in an
internal register after the conversion of analog data. This pin helps to
get the data out of the ADC0804. When CS=0, high to low pulse is
given to RD pin, then digital output comes on the pins D0-D7
WR: Write Pin
It is an input pin and is active low which is used to initiate the ADC
to start the conversion process.
When CS=0, WR makes a low to high transition, then ADC starts the
conversion process.
INTR: Interrupt
This is an output pin and is active low. When the conversion is over,
this pin goes low.
Vin+: Analog Input
Analog input to ADC.
Vin-: Analog Input.
Analog input connected to the ground.

7.  CLK IN and CLK R
CLK IN is an input pin connected to an external clock
source
To use the internal clock generator (also called self-
clocking), CLK IN and CLK R pins are connected to a
capacitor and a resistor, and the clock frequency is
determined by
 f = 1/1.1RC
 Typical values are R = 10K ohms and C = 150 pF
 We get f = 606 kHz and the conversion time is 110 us

8. Vref/2
It is used for the reference voltage
If this pin is open (not connected), the analog input voltage is in
the range of 0 to 5 volts (the same as the Vcc pin)
If the analog input range needs to be 0 to 4 volts, Vref/2 is
connected to 2 volts

9. D0-D7
The digital data output pins
These are tri-state buffered
The converted data is accessed only when CS = 0 and RD is forced
low
To calculate the output voltage, use the following
formula
Dout = Vin / Step Size
Dout = digital data output (in decimal),
Vin = analog voltage, and
step size (resolution) is the smallest change

10. Conversion Steps of ADC0804
1. Make CS = 0.
2. Send a low-to-high pulse to pin WR to start the
conversion.
3. Monitor the INTR pin. If INTR is low, the conversion is
finished but if the INTR is high, keep polling until it goes
low.
4. After the INTR has become low, we make CS = 0 and
send a high-to-low pulse to the RD pin to get the data out of
the ADC804.

13. DAC Interfacing with 8051
 Microcontroller are used in wide variety of applications like for
measuring and control of physical quantity like temperature,
pressure, speed, distance, etc.
 In these systems microcontroller generates output which is in digital
form but the controlling system requires analog signal as they don't
accept digital data thus making it necessary to use DAC which
converts digital data into equivalent analog voltage.
 In the figure shown, we use 8-bit DAC 0808. This IC converts digital
data into equivalent analog Current. Hence we require an I to V
converter to convert this current into equivalent voltage.

14. DAC Interfacing

15. MC1408 DAC (or DAC0808)
In this chip the digital inputs are converted to current.
The output current is known as Iout by connecting a resistor
to the output to convert into voltage.
The total current provided by the Iout pin is basically a
function of the binary numbers at the input pins D0 - D7
(D0 is the LSB and D7 is the MSB) of DAC0808 and the
reference current Iref.
The following formula is showing the function of Iout
The I ref is the input current. This must be provided into the pin 14.
Generally 2.0mA is used as I ref

16. GeneratingSine wave using DAC and 8051
DAC input values = 5v*25.6 =128

17. Source Code
Output