The document describes a data acquisition system using an AT89C51 microcontroller. It consists of the following: 1) Sensors measure physical quantities like temperature which are converted to analog signals. 2) A DAQ device with an ADC0808 analog to digital converter converts the analog signals to digital signals for processing by the microcontroller. 3) A MAX232 chip converts the voltage levels for communication between the microcontroller and a computer via an RS-232 serial interface. 4) An AT89C51 microcontroller samples the sensor signals using control signals to the ADC and transmits the digital readings to a computer to analyze and store the acquired data.

1. DATA ACQUISITION SYSTEM
USING AT89C51
PREM KUMAR
M-TECH (PED)
REG NO-1611110018

2. INTRODUCTION
The main objective of this project is to develop
the data acquisition system. In this project AT89c51 is
used to develop the data acquisition system

3. WHAT IS DAQ?
 Data acquisition (DAQ) is the process of
measuring an electrical or physical phenomenon such
as voltage, current, temperature, pressure, or sound
with a computer.
 DAQ systems either measure a physical
parameter or take a specific action (sound an alarm,
turn on a light, etc.) based on the data received.

4. DAQ SYSTEM
A DAQ system consists of sensors, DAQ
measurement hardware, and a computer with
programmable software
sensor DAQ DEVICE COMPUTER
DRIVER

5. BLOCK EXPLANATION
 First the sensor measures the physical quantity or
electrical quantity like
temperature, pressure, voltage or current.
 DAQ device which converts measured analog
signal into digital signal. And it is also interfaced
with PC.
 We can control the driver circuit by computer
through data acquisition system.

6. INTERFACING DIAGRAM

7. PIN DESCRIPTION
CONNECTED
TO ADC TO
SELECT
SENSOR
CONNECTED
TO DRIVER
CIRCUIT
CONNECTED
TO MAX 232
CONNECTED
TO ADC

8. ANALOG TO DIGITAL CONVERTER
ADC 0808 is 8 bit analog to digital converter, which
uses successive approximation type conversion.
Key specifications:
 Resolution 8 Bits
 Total Unadjusted Error ±½ LSB and ±1 LSB
 Single Supply 5 VDC
 Conversion Time 100 μs

9. MAX 232
 The RS232 is not compatible with 89c51,we
need a voltage converter to convert the RS232’s
signals to TTL voltage levels that will be acceptable
to the 89c51’s TxD and RxD pins.
 The MAX232 converts from RS232 voltage
levels to TTL voltage levels, and vice versa.one
advantage of the MAX232 chip is that we can use
same power supply(+5V) for controller and
MAX232.

10. PROGRAM
 Start : MOV P1,#00H
LCALL initserial
LCALL latch
LCALL start_conv
LCALL wait
LCALL get
MOV A,P2
MOV R6,A
LCALL send_read
SJMP Start

11. PROGRAM CONT….
delay :MOV R4,#80H
here : MOV R5,#30H
again : DJNZ R5,again
DJNZ R4,here
RET
initserial : MOV TMOD,#20H
MOV TH1,#FDH
MOV SCON,#50H
SETB TR1
SETB EA
SETB ES
RET

12. PROGRAM CONT….
start_conv : LCALL delay
CLR P3.3
LCALL delay
SETB P3.3
RET
wait : JB P3.4,wait
RET
get : LCALL delay
CLR P3.5
LCALL delay
SETB P3.5
RET

13. PROGRAM CONT….
send_char : MOV SBUF,R6
next : JNB TI,next
CLR TI
RET
send_read : LCALL send_char
MOV A,# “,”
LCALL send_char
RET
latch : CLR P3.6
LCALL delay
SETB P3.6
RET

14. CONCLUSION
Thus, the data acquisition system using
ATMEL89c51 microcontroller and ADC0808 is
designed. Also, proved it is more flexible as program
can be changed according to requirement repeatedly.