This document describes the design of a mixed signal system on chip (SoC) for temperature compensated pH measurement. The SoC uses a PSoC5 microcontroller from Cypress Semiconductor with analog and digital programmable blocks. Sensors measure the pH and temperature of a solution. The pH value is corrected using the Nernst equation based on the measured temperature. Experimental results show the SoC pH measurements match a standard pH meter and temperature sensor calibration. The SoC provides an accurate and reliable solution for integrated pH measurement.

2. MIXED SIGNAL VLSI TECHNOLOGY BASED SoC
DESIGN FOR TEMPERATURE COMPENSATED
pH MEASUREMENT
S. K. Tilekar1, A. S. Powar1 and B. P. Ladgaonkar1
1- VLSI Design & Research Centre
Post Graduate Department of Electronics
Shankarrao Mohite Mahavidyalaya, Akluj, Dist. Solapur (MS)
t_shivaprasad@rediffmail.com, bladgaonkar@yahoo.com

3. Abstract
An innovative field of embedded system exhibit wide
spectrum of applications particularly in the field of
instrumentation [1]. The VLSI devices like FPGA and CPLD
provide the reconfigurability for digital design only. Therefore,
for analog parts, the designers have to rely on off chip
hardware. This exhibits constraints in instrumentation [2]. The
emergence of the innovative technology called mixed signal
based VLSI design provides unique solution to above problem
[3]. Cypress semiconductor is performing pioneering job in the
field of mixed signal based programmable system on chip and
vendoring the PSoC5 device with remarkable features [4].
Deploying the features of PSoC5, a system on chip is designed
for temperature compensated pH measurement of the solution.
Keyword: Mixed Signal PSoC5, ADC, Programmable Gain
Amplifier, pH measurement.

4. Op
amp
LP
filter A/D Microcontroller
Op
ampD/A
Sensor
Digital Outputs
LEDs
Competitive Solutions

5. Op
amp
LP
filter A/D Microcontroller D/A
Sensor
Digital Outputs
LEDs
PSoC Microcontrollers

6.  Soft as well as hard IP Cores
 FPGA platform
 Core of the computing device
 Specific IDE for system development
SoB to SoC

7. Static as well as Dynamic configurability IP Cores
FPGA platform
Advanced microcontroller Core (ARM Core)
Specific IDE for system development
P rogrammable
S ystem
o n
C hip

8. – Hardware programmability
 Programmable analog blocks
 Programmable digital blocks
 Programmable interconnect
 Programmable I/Os
 Programmable clocks
 Selectable power supply
– Integration as an SoC

9.  32-bit ARM Cortex-M3 CPU core
 DC to 80 MHz operation
 Flash program memory, up to 256 KB, 100,000 write cycles, 20-year retention, and
multiple security features
 Up to 64 KB SRAM memory
 2-KB electrically erasable programmable read-only memory (EEPROM) memory, 1
million cycles, and 20 years retention
 Low voltage, ultra low power
 Wide operating voltage range: 0.5 V to 5.5 V
 Low power modes including: 2-μA sleep mode
 Versatile I/O system
 28 to 72 I/Os (62 GPIOs, 8 SIOs, 2 USBIOs)
 LCD direct drive from any GPIO, up to 46×16 segments
 All GPIOs configurable as open drain high/low, pull-up/pull-down, High-Z, or strong output
 Configurable GPIO pin state at power-on reset (POR)
 Digital peripherals
 20 to 24 programmable logic device (PLD) based universal digital blocks (UDBs)
 Full-Speed (FS) USB 2.0 12 Mbps using internal oscillator
 Four 16-bit configurable timers, counters, and PWM blocks
 Library of standard peripherals
 Library of advanced peripherals

10.  Analog peripherals
 1.024 V ±0.1% internal voltage reference across –40°C to +85°C (14 ppm/°C)
 Configurable delta-sigma ADC with 8- to 20-bit resolution
 Two SAR ADCs, each 12-bit at 1 Msps[2]
 80-MHz, 24-bit fixed point digital filter block (DFB) to implement finite impulse
response (FIR) and infinite impulse response (IIR) filters
 Four 8-bit 8 Msps current IDACs or 1-Msps voltage VDACs
 Four comparators with 95-ns response time
 Four uncommitted opamps with 25-mA drive capability
 Four configurable multifunction analog blocks. Example configurations are
programmable gain amplifier (PGA), transimpedance amplifier (TIA), mixer, and
Sample and Hold
 Programming, debug, and trace
 Precision, programmable clocking

13.  Voltage output ranges: 1.020-V and 4.080-V full scale
 Software- or clock-driven output strobe
 Data source can be CPU, DMA, or Digital components

14.  Gain steps from 1 to 50
 High input impedance
 Selectable input reference
 Adjustable power settings

15.  Single or differential connections
 Adjustable between 2 and 32 connections
 Software controlled
 Connections may be pins or internal sources
 No simultaneous connections
 Bidirectional (passive)

16.  Selectable resolutions, 8 to 20 bits (device dependent)
 Eleven input ranges for each resolution
 Sample rate 10 sps to 384 ksps
 Operational modes:
 Single sample
 Multi-sample
 Continuous mode
 Multi-sample (Turbo)
 High input impedance input buffer
 Selectable input buffer gain (1, 2, 4, 8) or input buffer
bypass
 Multiple internal or external reference options
 Automatic power configuration
 Up to four run-time ADC configurations

18.  Implements the industry-standard Hitachi HD44780 LCD display Driver
chip protocol
 Requires only seven I/O pins on one I/O port
 Contains built-in character editor to create user-defined
Custom characters
 Supports horizontal and vertical bar graphs

19.  Linear current output: 1 μA/K
 Wide temperature range: −55°C to +150°C
 2-terminal device: voltage in/current out
 Laser trimmed to ±0.5°C calibration accuracy (AD590M)
 Excellent linearity: ±0.3°C over full range (AD590M)
 Wide power supply range: 4 V to 30 V
 Sensor isolation from case
 Low cost

20. 1) The visual method
2) The photometric method
3) The potentiometric method

21. E = Eo – K Tk pH
Nernst Factor
K = 0.19841 (273.15+T oC)

22. Execute boot program:
--initialise general purpose resources;
--configure application specific modules;
--initialise run time environment;
--disable interrupt;
call main application routine;
Void main()
{
Start system timers;
Initialise application specific modules;
Initialise global variables;
Initialise application specific channels;
Enable interrupts;
While(1)
{
Wait for events(Enabled interrupts);
Read values from input channels;
Execute control procedure & compute
actuation data;
output actuation data to output
channels;
}
}
B) Application programme routine
A) Boot programme algorithm
STRUCTURE OF FIRMWARE

23. #include <device.h>
#include <stdio.h>
float pH_Input_Signal();
float Temp_Input_Signal();
void soft_delay(unsigned int count);
int i=1,j=1;
float result=0,pH_Result,Average_pH,pH_value,pH_Temp_Copensated,pH_valueDirect;
float Temp_Result,Temp_value,Average_Temp,Temp_Calibrated;

24. void main()
{
char pH_Str[5]={'0'};
PGA_1_Start(); PGA_2_Start(); VDAC8_1_Start(); LCD_Char_1_Start();
ADC_DelSig_1_Start(); char Temp_Str[4]={'0'}; AMuxSeq_1_Start();
while(1)
{
AMuxSeq_1_Next(); LCD_Char_1_Position(0,0); LCD_Char_1_PrintString("T:");
Temp_Result=Temp_Input_Signal(); Temp_value = Temp_Result-273;
Temp_Calibrated=(Temp_value+0.7503)/1.0377;
LCD_Char_1_Position(0,2); sprintf(Temp_Str,"%4.2f",Temp_Calibrated);
LCD_Char_1_PrintString(Temp_Str);
MuxSeq_1_Next();
LCD_Char_1_Position(1,0); LCD_Char_1_PrintString("pH:");
pH_Result=pH_Input_Signal();
pH_value = (pH_Result)/(0.19841*(273.15+Temp_Calibrated)); //Nernst equation
LCD_Char_1_Position(1,3); sprintf(pH_Str,"%5.2f",pH_value);
LCD_Char_1_PrintString(pH_Str);
pH_valueDirect = ((pH_Result-24)/59.16); LCD_Char_1_Position(0,9);
sprintf(pH_Str,"%5.2f",pH_valueDirect); LCD_Char_1_PrintString(pH_Str);
} }

25. float pH_Input_Signal()
{
float total=0,Sampling_Rate=1000;
for(i=1;i<=Sampling_Rate;i++)
{
ADC_DelSig_1_StartConvert();
ADC_DelSig_1_IsEndConversion(ADC_DelSig_1_WAIT_FOR_RESULT);
total=total+ADC_DelSig_1_GetResult16();
soft_delay(1000);
}
Average_pH=((total/Sampling_Rate)*3);
return(Average_pH);
}

26. float Temp_Input_Signal()
{
float total=0,Sampling_Rate=750;
for(j=1;j<=Sampling_Rate;j++)
{
ADC_DelSig_1_StartConvert();
ADC_DelSig_1_IsEndConversion(ADC_DelSig_1_WAIT_FOR_RESULT);
total=total+ADC_DelSig_1_GetResult16();
soft_delay(2000);
}
Average_Temp=((total/Sampling_Rate)*4);
return(Average_Temp);
}

28. y = 1.0515x - 3.22
R² = 0.9989
0
20
40
60
80
100
120
0 50 100 150
Temperature in oC from Thermometer
TemperatureinoCfromSystem

29. Temp Measured
(Thermometer)
Temp Measured
(PSoC)
40 39.94
45 44.94
50 49.97
55 54.93
60 59.95
65 64.95
70 69.91
75 75.01
80 80.01
85 85.02
90 90.41
95 95.52
100 100.56

30. Temp Measured in o
C
(Thermometer)
Temp dependent
NERNST volt in mV
From system (PSoC)
Temp dependent
NERNST volt in mV
From datasheet
20 58.18 58.16
25 59.17 59.16
30 60.16 60.15
35 61.13 61.14
40 62.13 62.13
45 63.14 63.12
50 64.13 64.12
55 65.12 65.11
60 66.12 66.10
65 67.11 67.09
70 68.09 68.08
75 69.10 69.08
80 70.09 70.07

31. The system is calibrated to pH scale and
implemented for measurement of temperature compensated
pH of the solution. The pH value shown by the system under
investigation are identical to that of measured by standard
pH meter. Thus SoC designed to measure pH of the solution
is more reliable and accurate.

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33. Research Activities
MRP : 01 Completed
Publications
: International Journals 01
: International Journals (Communicated) 01
: National Journals 01
: National Journals (Communicated) 01
: Proceedings International 02
: Proceedings National 42
Papers presented in conferences
: International 01
: International (Abroad) 01
: National 12