单片机英文资料.doc

50
AN EMBEDDED SINGLE CHIPTEMPERATURE
CONTROLLER DESIGN
J. Jayapandian and Usha Rani Ravi
Design Development & Services Section, Materials Science Division
Indira Gandhi Centre for Atomic Research, Kalpakkam – 603 102. Tamil Nadu. India
ABSTRACT
This paper describes a single chip embedded temperature controller design programmed
in a single Programmable System on Chip (PSoC); a mixed array logic consists of analog,
digital and digital communication blocks within in it. The virtual instrument control
program written in LabVIEW ver.7.1, a graphical language, provides user friendly menu
driven window based control panel, interacts with the single PSoC chip design for sensing
and controlling the temperature. This simple cost effective embedded design finds
potential application in laboratory as well as in industries. This deign can also be made
as a standalone system without PC by programming LED/ LCD display and key pad
attachment modules in same PSoC chip.
1. INTRODUCTION
The advent of intelligent programmable embedded silicon designs provides the ability to
implement any required hardware programmatically for the design automation in industries
and laboratories. Recent trend in laboratory as well as in industrial automation designs uses
minimal hardware and maximum support of software. The programmable embedded
components and application software available in the market enables the designer for userfriendly
cost effective design solution for any system automation. Temperature controllers
are playing vital role in industries and laboratories. To accurately control process temperature
without extensive operator involvement, a temperature control system relies upon a controller,
which accepts a temperature sensor such as a thermocouple or RTD as input. It compares
the actual temperature to the desired control temperature, or set point, and provides an output
to a control element. The controller is one of the major parts of the entire control system,
and the whole system should be analyzed in selecting the proper controller. This paper
describes a novel single chip temperature controller design with Cypress Microsystems
Programmable System on Chip (PSoC). Virtual instrument control program written in LabVIEW
ver.7.1 interacts with the embedded PSoC design and senses and controls the temperature of
furnace / load.
J. Instrum. Soc India 38(1) 50-54
51
2. PROGRAMMABLE SYSTEM ON CHIP (PSoC)
While selecting a microcontroller, it must have an easy and inexpensive interface to
sensors, communication interfaces, and more. Cypress’ Programmable System-On-Chip (PSoC)
architecture offers a flexible, economical solution for a wide variety of applications. This paper
describes the design of a temperature controller on a single CY8C27143, 8 pin PSoC chip. As
shown in fig.1, it features four main areas: PSoC core, digital system, analog system, and
system resources including in/out ports. This architecture allows the user to create customized
peripheral configurations that match the requirements of each individual application. The UART
interface, coupled with configurable analog and digital peripherals makes the CY8C27143 truly
universal in its connections to the external world. The PSoC core includes: an M8C
microcontroller; 32 Kbytes of program flash memory; 2 Kbyte of data RAM; internal 24 MHz
oscillator; sleep and watchdog timer; general-purpose input/ output pins (GPIO) allowing any
pin to be used as digital input or output, and most pins to be used as analog inputs or outputs.
Every pin can be used as a digital or analog interrupt. The digital system is made up of 8
digital PSoC blocks. Each block is an 8-bit resource that can be used alone or combined with
other blocks to form peripherals. Possible peripherals include: PWMs (8- to 32-bit); PWMs
with dead band (8- to 24-bit); counters (8- to 32-bit); UART 8-bit with selectable parity; SPI
master and slave; cyclical redundancy checker/generator (8- to 32-bit); pseudo random
sequence generators (8- to 32-bit). These digital blocks can be connected to any of the GPIO
through a series of global buses. These buses also allow for signal multiplexing and performing
logic operations. The analog system is made up of 12 configurable blocks, each comprising
an op amp circuit allowing the creation of complex analog signal flows. Analog peripherals
Fig. 1 : Block diagram of Programmable System on Chip (PSoC) internal blocks
An embedded single chip temperature controller design
52
are very flexible and can be customized to support specific application requirements. Some
of the more common PSoC analog functions are: filters (2- and 4- pole band-pass, low-pass,
and notch); amplifiers (up to 2, with selectable gain to 48x); instrumentation amplifiers (1
with selectable gain to 93x); comparators (up to 2, with 16 selectable thresholds); DACs (up
to 2, with 6- to 10-bit resolution); and SAR ADCs (up to two, with 6-bit resolution). In
combination with the digital blocks, additional functions can be created, including: incremental
ADCs (up to 2, with 6- to 14-bit resolution); delta sigma ADC (1,with 8-bit resolution at
62.5ksps). The additional system resources provide additional capability useful for the complete
system design.
3. VIRTUAL INSTRUMENT PROGRAM
Virtual instrument (VI) is an application of general purpose digital PCs for the measurement
and control of various physical variables. The VI program mimics the control processes, which
are in a remote area, on the PC screen. On-going process control automation can be visualized
by the experimentalist through PC screen. VI program provides inexpensive and yet a powerful
platform for the control and data acquisition of process variables. These programs are easy
to implement with graphic languages (G-language). The “G” language implements the data
flow technique. The usage of “G” language VIs provides easy interfacing with PCs under the
Windows environment [2]. The “G” language provides built-in function libraries for a variety
of application requirements as graphic palettes, which in turn supports the required DLLs for
the functions to run under windows environment. Usually the “G” language VI programs consist
of two frames viz., panel diagram and functional diagram. In the panel diagram,
programmers can assign various controls and indicators (i.e., input and output variables) as
per their requirements and in the functional diagram, the designers can implement the required
J. Jayapandian and Usha Rani Ravi
Fig. 2 : PSoC designer screen for single chip temperature controller
53
functions available as a function library in LabVIEW. National Instruments LabVIEW version
7.1 incorporates all the necessary functions as ‘icons’ in its package.
4. PSoC SINGLE CHIP TEMPERATURE CONTROLLER DESIGN
Fig.2 shows the PSoC designer screen for the embedded single chip (8 pin PSoC chip
CY827143) temperature controller design project [1]. Left side of the screen shows the settings
of global resource and user module parameters along with pin connectivity configuration. Middle
portion of the screen shows the analog and digital blocks user module placement. Top portion
of the screen shows the selected user modules for this project. Right side of the screen
describes the pin connectivity configured in the design. In this novel single chip design,
thermocouple (TC) signal has been amplified by a programmable gain amplifier (PGA) placed
in the PSoC’s analog block. The amplified TC signal has been fed in to a 12 bit Analog-todigital
(ADC) user module programmed in the PSoC chip, which includes both analog and
digital blocks for its functionality by PSoC designer programming. The converted digital data
of the amplified TC signal has been fed to the UART user module for serial communication
with Personal Computer. The UART user module placed in the PSoC chip, automatically gets
placed in two digital blocks of PSoC chip, transmitter (TxD) and receiver (RxD) for PCs serial
communication. A pulse width modulator (PWM), placed in the PSoC digital block, sets a
serial pulse width modulated TTL pulses in response to the PID control function for the
deviation in set and measured temperature. This will in turn controls the optically coupled
solid state relay (SSR) driving the AC line power connected to the load/furnace [3,4]. The
menu driven window based virtual instrument control program senses the temperature, via,
thermocouple, TC amplifier, 12-bit ADC and UART communication block of PSoC chip and
evaluate the control functions like P,I,D, linear heating, on-sweep and sets the pulse width of
PWM in a PSoC chip via UART block in a serial communication.
An embedded single chip temperature controller design
Fig. 3 : Single PSoC chip Temperature controller design
54
Fig.3. shows the connectivity of a single PSoC chip design with solid state relay (SSR)
and USB port via, serial-to-USB converter cable for communication with PC. The SSR, acts
as AC power controller for controlling the furnace power, has been activated by the PWM
pulses from PSoC chip. The menu driven virtual instrument control program works in window
environment interacts with the embedded design for sensing, controlling and acquiring the
temperature data. On-line plotting of acquired temperature data also carried out by the VI
program.
5. CONCLUSION
A simple and cost effective embedded temperature controller has been designed, fabricated
and tested successfully for its functionality. This compact designs permits the user to select
any type of control function through its virtual instrument program, written in LabVIEW
7.1, and works under window environment. This design can be directly connected to PCs
‘com’ port or USB port via USB-to-serial converter cable, the SSR power controller module
can be connected on the furnace stand. The optically isolated power controller provides safe
operation without damaging the interfacing intelligent controller.
6. REFERENCES
1. J. Jayapandian. Current Science, Vol 90. No.6. 25th March 2006. p.765-770.
2. National Instrument’s LabVIEW user manual.
3. J. Jayapandian. Design Briefs. Electronic Design Magazine. A Penton Publication.New Jersey,
USA.
ED Online ID #5687. September 15, 2003.
4. J. Jayapandian et.al. J. Instrum. Soc. India 33 (2) 75 – 80 (2003).
J. Jayapandian and Usha Rani Ravi