Microprocessor Based Temperature Controller

1. PROCESS CONTROL IN WET TANNERY
 The block diagram of the process can be interpreted as:
.
Get Input Converting the Interfacing the
Signal signal with
Signal from signal to
Conditioning 8085
Sensor digital form
microprocesor
Load Interfacing Programming the
Circuit. Microprocessor
4

2. INPUT FROM SENSOR
 For temperature sensing LM35 Temperature
sensor is used.
 The output voltage of this 3 pin temperature sensor
is directly proportional to the ambient temperature
and is given by the formula:
Vout = K x T
Where,
K = 10mV/oC (Sensor Constant),
T= Ambient Temperature.
 For a temperature range of 0-100oC, the output
voltage varies from 0-1V in steps of 10mV. 2

3.  For pH sensing, PHE-45P pH sensor is used.
 The PHE-45P is an electrode type sensor, which
develops a voltage(potential) directly proportional to
the concentration of H+ ions.
 For a pH range of 0-14, the output voltage of the
sensor varies from -0.41V to +0.41V.
3

4.  The output voltage from the pH sensor follows Nernst
equation of equilibrium reduction potential.
Where,
E = reduction potential(voltage generated)
R = Universal gas constant( R=8.314 J/K-mol)
T = absolute temperature(T = 298K)
F = Faraday constant(F = 96485.33C/mol)
z = number of ions involved in the reaction.
4

5.  On substituting the values of constants, we get:
E = 0.4142 – 0.059pH.
Hence, for a pH of 7, the potential would be 0,
for a pH of 0 (pure acidic), E = 0.41V
for a pH of 14(pure alkaline), E = -0.41V.
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6. SIGNAL CONDITIONING
 The signal conditioning is done so as to interface
the sensor’s output with the Analog to digital
converter.
 The main aim of this module is to convert the output
of sensors i.e., 0-1V from temperature sensor and -
0.41V to +0.41V from pH sensor to 0-5V which is
the acceptable working range for an analog to
digital converter.
6

7.  For temperature sensor, we use a simple non
inverting amplifier circuit, given below:
Voltage Gain(A) = 5v/v.
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8.  For pH sensor, we use an adder circuit coupled with
an inverting amplifier:
The output voltage is 0-5V.
8

9. CONVERTING TO DIGITAL FORM
 ADC0809 is used for analog to digital conversion.
The analog signal which we get from the sensors is
amplified to 0-5V and is given to the ADC 0809.
 The analog input from the temperature sensor is
given at IN0 port of ADC.
 The input port selection is done through the input
selection lines(ADD A, ADDB, ADD C) which are
connected to the programmable peripheral interface.
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10.  The conversion starts when SOC(Start of
Conversion) is given HIGH from the microprocessor
through 8255.
 When the analog input is converted to digital form,
the EOC(End of Conversion) port goes HIGH,
informing the microprocessor that the conversion is
done.
 The clock to the ADC is given from the
microprocessor clock output.
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11. ADC 0809 PIN CONNECTION
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12. INTERFACING WITH MICROPROCESSOR
 The digital output from the ADC is interfaced with
the microprocessor through a programmable
peripheral interface (PPI 8255).
 PPI 8255 is a 40 pin IC which consists of three 8-
bit I/O ports, a 8-bit Bi-directional data transfer port
and a control logic buffer.
 The block diagram of 8255 is as follows:
12

13. .
13

14. • Data Bus Buffer: It is an 8 bit data buffer used to
interface 8255 with 8085. It is connected to D0-D7 bits
of 8255.
• Read/write control logic : It consists of inputs
RD¯,WR¯,A0,A1,CS¯ .
• RD¯,WR¯ are used for reading and writing on to 8255
and are connected to MEMR¯,MEMW¯ of 8085
respectively.
• A0,A1 are Port select signals used to select the
particular port .
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• CS ¯ is used to select the 8255 device .

15. A1 A0 Selected port
0 0 Port - A
0 1 Port –B
1 0 Port – C
1 1 Control Register
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16. The 8255 PPI is initialized as below:
 Port A - Assigned as Input
 Port B - Assigned as output
 Port CL - Assigned as Input
 Port CU - Assigned as output
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17.  The Port A takes input from the digital output pins of
ADC.
 The Port B gives signal to SOC, ALE and Input
Select of ADC.
 The Port CL takes input from EOC.
 The Port CU gives the control signal.
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18.  Control Word:
 The control word for the PPI is – 1 0 0 1 0 0 0 1 i.e.,
91H.
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19. 19

20. MICROPROCESSOR 8085
The features of INTEL 8085 are :
 It is an 8 bit processor.
 It is a single chip N-MOS device with 40 pins.
 It has multiplexed address and data bus.(AD0-AD7).
 It works on 5 Volt dc power supply.
 The maximum clock frequency is 3 MHz while
minimum frequency is 500kHz.
 It provides 74 instructions with 5 different addressing
modes.
 It provides Acc ,one flag register ,6 general purpose
registers and two special purpose registers(SP,PC). 20

21. PIN LAYOUT.
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22. INTERNAL ARCHITECTURE:
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23. INSTRUCTION SET CLASSIFICATION
The entire group of instructions can be classified into five
categories:
1. Data Transfer Operations. E.g. MOV, MVI, LDA,STA.
2. Arithmetic Operations. E.g. ADD, SUB, INR, DCR.
3. Logical Operations. E.g. ANA, ORA, XRA, CMP.
4. Branching Operations. E.g. JMP, CALL, RET, JZ.
5. Machine Control Operations. E.g. IN, OUT, PUSH, POP.
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24. . PROGRAMMING LOGIC:
.
• Configure 8255 I/O ports
• 8085 sends SOC command to ADC
• 8085 waits for EOC signal from ADC
• 8085 reads 8-bit temperature value from
port A
• 8085 compares the value with set point
value
• 8085 generates the control signal to
control load. 24

25. FLOW CHART
 .
. START
.
Initialize 8255
CALL CONVERSION
Is
Temp
>
SETPP
T
25
Turn heater off

26. 26

27. PROGRAM:
MVI A, 91H
OUT CR
BEGIN: CALL CONVERSATION
CPI 41H
JC NEXT
MVI A, 0EH
OUT PC
JMP BEGIN
NEXT: MVI A, 0FH
OUT PC 27
JMP BEGIN

28. CONVERSION SUBROUTINE:
CONVERSION:
MVI A,00H
OUT PB ; Send address to select IN0
MVI A,08H ;Latch address by giving ALE High
OUT PB
BACK: MVI A,18H
OUT PB ; Make SOC High
MVI A,08H
OUT PB ; Make SOC Low
MVI A,00H
OUT PB ; Make ALE Low
LOOP: IN PC
ANI 01H
JZ LOOP; Wait for EOC
IN PA
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RET ; Return value and store Accumulator

29. INTERFACING CIRCUIT
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30.  The load, in this case a heater, is a device which
operates under 230V ac.
 The control signal from the microprocessor through
the peripheral interface is of 5V magnitude.
 A solid state relay device is used to interface the
control signal with the load.
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