1.0 Introduction
An AC voltmeter with microprocessor seven segments display is an instrument that measures AC voltage and output the measured voltage digitally through the help of the seven segment display unit and it can be said to be a digital voltmeter because it is designed around a special type of analog-to-digital converter called an integrating converter.
The voltmeter accuracy is affected by many factors; including temperature and supply voltage variations. To ensure that a digital voltmeter reading is within the manufacturer's specified tolerances it should be periodically calibrated against a voltage standard such as the Weston cell.
This project has five stages as shown in the block diagram below (You will get the diagram in the complete work at i will give you at the end of this page)
Fig 1.1 Block Diagram of an AC Volt meter using Microprocessor with seven segment display.
1.1.0 Power Supply:
This section of the circuit has to do with the power available for utilization in the circuit and will be further broken down into the following stages.
1.1.1 Transformation Stage:
To measure the voltage available from an ac source. The probes of the instrument will have to be inserted or connected to the neutral and life terminals respective. Considering the fact that voltage between a line and neutral should be between 220 to 240 volts ideally, a step down transformer (240/12VAC) was employed in the design to step down the 240v to 12v as the case may be.
1.1.2 Rectification Stage:
Because sensitive and delicate electronic devices like ICs (integrated circuits) are not powered using AC but DC, the 12v AC supply was rectified using a diode D1. a diode is sometimes called a rectifier because of its application in changing AC to DC. But the output of a rectifier circuit consists of a DC component and an AC component (also known as ripples). The AC component is undesired and accounts for pulsations in the rectified output.
1.1.3 Filtration:
Because of the presence of AC components in the rectifier output which of course is undesirable because a rectifier is required to produce DC supply for using at various places in the electronic circuit, the filter circuit is employed to filter the AC component. A filter circuit is a device which removes AC component of rectifier output but allows the DC component to reach the load.
1.1.4 Voltage Regulation Stage:
The output from diode D1 is still 12v which goes to the 7805 regulator. The 7805 is a regulator which regulates the input 12v and gives output of 5v because the ADC and PIC 16f 84A requires 5v for its powering.
1.15 Analog To Digital Converter (Adc):
IC1 is an ADC which converts the input analog to digital through the reference point. This measures the average value of the input voltage over a fixed integrated period. The basic idea of this device is to a pulse width proportional to the analog input voltage by making the time comparison between two integration.
The first integration is the unknown input analog signal, it proceeds for a fixed interval of time equal to the maximum number of counts times the clock period. The input is then switch to a known reference voltage. R1 is a variable resistor which varies the voltage into the ADC.
1.16 Micro Processor:
IC2 is a micro processor which decodes the out coming data from ADC and processes the incoming data so as to give an output to BCD 7 segment decoder.
1.17 Seven Segment Bcd Decoder:
The BCD 7 segment decoder decodes the binary coded decimal to from the processor to give an output to the display unit. It receives its input from the processor via the 4 pins labeled ABCD and give a corresponding output from 7 pins; 0A, OB, OC, OD, OE, of and OG which tarries with the 7 segment of the display.
1.18 Seven Segment Display:
The seven segment display unit. One common requirement for many digital devices is a visual numeric display and this is used in this project to display the numeric value of the measured voltage.
1.2 Objectives
The objective of this project work is to construct a voltmeter that can be used to measure AC voltages and can be mounted on panel to monitor generator output voltage and other fixed apparatus
1.2 Definition of Terms
1.2.1 Voltmeter:
An instrument for the measuring the electric potential difference between two point in a circuit. Digital voltmeter gives a numerical display of voltage by use of an analog to digital converter.
1.2.2 Microcontroller:
A microcontroller (also microcontroller unit, MCU or µC) is a small computer on a single integrated circuit consisting of a relatively simple CPU combined with support functions such as a crystal oscillator, timers, watchdog, serial and analog I/O etc. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a, typically small, read/write memory.
The first single chip microprocessor was the 4 bit Intel 4004 released in 1971, with other more capable processors available over the next several years. These however all required external chip(s) to implement a working system, raising total system cost, and making it impossible to economically computerise appliances.
1.2.3 Analog-To-Digital Converter:
The ADC0803 family is a series of three CMOS 8-bit successive approximation A/D converters using a resistive ladder and capacitive array together with an auto-zero comparator. These converters are designed to operate with microprocessor-controlled buses using a minimum of external circuitry. The 3-State output data lines can be connected directly to the data bus.
The differential analog voltage input allows for increased common-mode rejection and provides a means to adjust the zero-scale offset. Additionally, the voltage reference input provides a means of encoding small analog voltages to the full 8 bits of resolution.
1.2.4 Seven (7) Segment Display:
The 7-segment displays are very common components of digital devices, it is good to be familiar with the “driving” circuits behind them, and the 4511 is a good example of a typical driver IC. Its operating principle is to input a four-bit BCD (Binary-Coded Decimal) value, and energize the proper output lines to form the corresponding decimal digit on the 7-segment LED display.
The BCD inputs are designated A, B, C, and D in order from least-significant to most-significant. Outputs are labeled a, b, c, d, e, f, and g, each letter corresponding to a standardized segment designation for 7-segment displays. Of course, since each LED segment requires its own dropping resistor, we must use seven 470 O resistors placed in series between the 4511's output terminals and the corresponding terminals of the display unit.
The project work has four sections which are;
- The power supply section powers the ADC with a rectified and regulated voltage of 5v and also the voltage is used to power the whole circuit.
- The ADC translates the analog data to binary code required for data processing and transmission in control system.
- The microcontroller processes the data received from the ADC and sends it to the decoder.
- The decoder decodes the processed signal from the microprocessor and displays it on the seven segment display unit as an output voltage.
This project work can not be easily carried out as digital voltmeter through any other means or process except as analog voltmeter.
1.2.5 Transformer:
A transformer is a static (or stationary) piece of apparatus by means of which electric power in one circuit is transformed into electric power of the same frequency in another circuit. It can raise or lower the voltage in a circuit but with a corresponding decrease or increase in current.
The physical basis of a transformer is mutual induction between two circuit linked by a common magnetic flux. In its simplest form, it consists of two inductive coils which are electrically separated but magnetically linked through a path of low reluctance as shown below.
The material contains electrical diagrams, circuits, illustrations and more (Very detailed)
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