16-Channel Data Acquisition System(DACQ)

1) Introduction

Data acquisition systems, as the name of this system implies, are processes used to assemble information to paper or analyze some phenomenon. In the simplest form, a technician logging the temperature of an oven on a piece of paper is performing data acquisition. As technology has progressed, this type of process has been simplified and made more accurate, versatile, and reliable through electronic equipment. Equipment ranges from simple recorders to intricate computer systems. Data acquisition products serve as a focal point in a system, tying together a wide variety of products, such as sensors that are a sign of temperature, pressure, flow, or level, some common data acquisition terms are shown below.

Analog to digital converter (A/D) -this electronic device is used to converts analog signals to an equivalent digital form. The analog-to-digital converter is the heart of most data acquisition systems.

Digital-to-Analog Converter (D/A)-this electronic component found in many data acquisition devices that produce an analog output signal.

Digital Input/output (DIO)-this device Refers to a type of data acquisition signal. Digital I/O is discrete signals which are either one of two states. These states may be on/off, high/low, 1/0, etc. Digital I/O is also referred to as binary I/O.

Differential Input-Refers to the way a signal is wired to a data acquisition device. Differential inputs have a unique high and unique low connection for each channel. Data acquisition devices have either single-ended or differential inputs, many devices support both configurations.

RS232-A standard for serial communications found in many data acquisition systems. RS232 is the most common serial communication; however, it is somewhat limited in that it only supports communication to one device connected to the bus at a time.

Sample Rate -The speed at which this system collects data. The speed is normally expressed in samples per second. For multi-channel data acquisition devices the sample rate is typically given as the speed of the analog-to-digital converter (A/D). To obtain individual channel sample rate, need to divide the speed of the A/D by the number of channels being sampled.

1.1) Aim

This report presents the work out of how with the use of advanced pressure sensors qualify under production purpose o deal with the various tasks.

1.2) Overview of ADC0816, ADC0817

The ADC0816/ADC0817 data acquisition component is a Monolithic CMOS device with an 8-bit analog-to-digital converter, 16-channel multiplexer and microprocessor compatible control logic. These two devices are similar to ADC0808/ADC0809 except these have 16 analog input signals instead of 8.and the multiplexer output and A/D comparator inputs are externally available but in ADC0808/09 its connected internally. This feature is useful when connecting signal connecting circuitry to the A/D. ADC0816/17 also have an expansion control pin to allow the addition of more multiplexers. That’s why more input channels. The ADC0816 is identical to ADC0817 except accuracy point of view the ADC0816 having the more accuracy part with the total adjusted error of ±1/2 LSB and in the same way the ADC0817 have ±1 LSB. So in many applications where the slightly low accuracy is needed the ADC0817 represents a more economical solution.

Block diagram of Data acquisition system

Requirement Analysis

2) Requirement analysis

2.1) Problem description

Following were the procedures to be followed for designing the proposed circuit onto the printed circuit board:

Create the schematic diagram on by the use of ISIS software from circuit diagram

Converting the schematic diagram to PCB layout

Designing the PCB layout for the schematic capture

Get the fabrication done from PCB Lab,

Populating and soldering the components.

Write the program and transfer it to flash onto controller then

Test the functionality

2.2) Components required

The following components were required the finalized the design:

Software to draw the schematic diagram and to PCB Layout

Drilling machines

Fabricated board

Circuit components

Soldering tools

DC Power supply unit

Voltmeter

Pair of cords

Tektronix oscilloscope

3) Possible Solution

MEMS type Pressure sensor under the final validation

Figure shows the possible solution diagram to solve this problem that was needed for this task

Components Required

The major components that were used in this particular design are MEMS Pressure Sensors, Signal conditioning, ADC0816, 89C52 controller, LCD 20×4 display, MAX 232

MICROCONTROLLER- AT89C52:

The 8952 microcontroller is upgraded version of 8051 family of microcontrollers. The 8051 microcontroller was introduced by Intel Corporation in the year 1981. It is an 8-bit microcontroller with Harvard Architecture manufactured by advanced CMOS processes. It has 128 bytes of on chip RAM, 4k bytes of on chip ROM, two 16-bit timers/counters, four 8-bit ports of which one is a serial port, etc. There are 6 interrupt sources also. Since this is an 8-bit micro controller, the CPU can work on only 8 bits of data at a time. Data larger than 8 bits has to be broken down to 8 bit pieces. Though it has an addressing capability of 64 Kbytes, only 4k bytes have been provided on chip.

MAX-232

IC is used to convert the TTL/CMOS logic levels to RS232 logic levels during serial communication of microcontrollers with PC. The controller operates at TTL logic level (0-5V) whereas the serial communication in PC works on RS232 standards (-25 V to + 25V). This makes it difficult to establish a direct link between them to communicate with each other.

Micro-Electro-Mechanical Systems (MEMS)

Micro-Electro-Mechanical Systems or MEMS is a precision device technology that integrates mechanical elements, sensors, actuators, and electronics on a common silicon substrate through micro fabrication technology. MEMS are also referred to as MST (Microsystems Technology in Europe) and MM (Micro machines in Japan). MEMS with optics are called MOEMS- Micro-Opto-Electro-Mechanical-Systems).

Signal Conditioning Process

Signal conditioning process

Signal conditioning Means manipulating an analog signal in such a way that it meets the requirements of the next stage for further processing. Most common use is in analog-to-digital converters.

The process of signal conditioning

Signal conditioning process including Buffering, amplification, filtering converting, range matching etc.

Buffering

Is a process to buffer the input signal and keep this signal as usual for the next?

Filtering

This is the most common signal conditioning function, as usually not all the signal frequency spectrum contains valid data. The common example is 50Hz AC power lines, present in most environments, which will produce noise if amplified. So this step of signal conditioning removed the noise and other distortions from the input signals

Amplifying

Signal amplification performs two important functions: increases the resolution of the given input signal, and increases its signal-to-noise ratio. For example, the output of an electronic temperature sensor which is most likely in the mill volts range so possibly it is too low for an ADC to process directly. So in this case it is very necessary to bring the voltage level up to the level that is required by ADC.

Commonly used amplifiers on signal conditioning process include Sample and hold amplifiers, Peak Detectors, Log amplifiers, Antilog amplifiers, Instrumentation amplifiers or programmable gain amplifiers.

Isolation

This process of Signal isolation is required to use in order to pass the signal from the source to the measurement device without a physical connection. It is frequently used to isolate or separate possible sources of signal disorder. Also prominent is that’s it is important to separate the potentially expensive equipment after completing the process of conditioning.

Project Source Code

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#include<reg51.h>
sbit ale=P2^1;  //address latch enable
sbit oe=P2^0;  //output enable
sbit sc=P2^2;  //start conversion
sbit eoc=P2^7;  //end of conversion
sbit ADD_A=P1^1;  // Address pins for selecting input channels.
sbit ADD_B=P1^2;
sbit ADD_C=P1^3;
 
sfr addr_port=0x90;  //p1 por
sfr data_port=0x80;  //p0 port
 
unsigned char k, data_buffer;
 
void transmit();
void delay(unsigned int count);
        
void transmit()  //serial port transmission
{
            SBUF=k;
            while(TI==0);
            TI=0;
 
            SBUF=data_buffer;
            while(TI==0);
            TI=0;
}
 
void delay(unsigned int count)  // Function to provide time delay in msec.
{
            int i,j;
            for(i=0;i<count;i++)
            {  
                        for(j=0;j<1275;j++);
            }
}
 
void main()
{
            data_port=0xFF;
            delay(2);
            ale=0;
            oe=0;
            sc=0;
            TMOD=0x20;
            TH1=0xFD;  //timer1 setting for serial communication
            SCON=0x50;
            TR1=1;
 
            while(1)
            {
                        for(k=0; k<=15; k++)
                        {
                                    addr_port=k;
                                    delay(2);
                                    ale=1;
                                    delay(2);
                                    sc=1;
                                    delay(1);
                                    ale=0;
                                    delay(1);
                                    sc=0;
                                    while(eoc==1);
                                    while(eoc==0);
                                    oe=1;
                                    data_buffer=data_port;
                                    transmit();
                                    delay(2);
                                    oe=0; 
                        }
                        if (k==15)
                        {
                                    k=0;
                        }
            }
}
 
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