-SS Murthy Tumuluri
Srinath D Prem Chand K Naveen Kumar
A voltmeter finds its importance wherever voltage is to be measured. A voltmeter is an instrument used for measuring the electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit. General purpose analog voltmeters may have an accuracy of a few per cent of full scale, and are used with voltages from a fraction of a volt to several thousand volts. Digital voltmeters give a numerical display of voltage by use of analog to digital converter. Digital meters can be made with high accuracy, typically better than 1%. Specially calibrated test instruments have higher accuracies, with laboratory instruments capable of measuring to accuracies of a few parts per million. Meters using amplifiers can measure tiny voltages of micro-volts or less. Digital voltmeters (DVMs) are usually designed around a special type of analog-to-digital converter called an integrating converter. Voltmeter accuracy is affected by many factors, including temperature and supply voltage variations. To ensure that a digital voltmeter's reading is within the manufacturer's specified tolerances, they should be periodically calibrated. Digital voltmeters necessarily have input amplifiers, and, like vacuum tube voltmeters, generally have a constant input resistance of 10 mega-ohms regardless of set measurement range. This project aims at building a Digital Voltmeter using an 8051 microcontroller. All the data accessed and processed by the microcontroller is the digital data. And thus, the usage of an analog-to-digital converter finds its necessity here. A standard analog-to-digital converter ADC0804 is used in the current project. The input voltage (which is the analog input) is restricted to be in the range of 0-15V. The processed data in the 8051 is used to drive a display output on a LCD display unit. The display is in the form of digits and is accurate to a value of one decimal. The input voltage is desired to be that of a DC voltage for steady observations of the voltage value on the LCD panel. Rather, if an AC input voltage is given at the input terminals, the output varies indefinitely as is the nature of AC voltage. Thus, the instantaneous value of the AC voltage is not steadily shown on the LCD panel.
Following is the entire set of the components used to build the Digital Voltmeter: 1.Microcontroller, AT89S52
2.Analog-to-Digital Converter, ADC0804
4.Oscillator circuit for the microcontroller
4.112MHz Crystal Capacitor
5.Voltage divider circuit/ Input terminals
5.1200k, 100k Resistors
6.ADC Clock Circuit
7.100k Potentiometer (to adjust the back-light of the LCD)
The AT89S51 is a low-power, high-performance CMOS 8-bit microcontroller with 4K bytes of In-System Programmable Flash memory. The device is manufactured using Atmel’s high-density non-volatile memory technology and is compatible with the industry-standard 80C51 instruction set and pin-out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional non-volatile memory programmer. By combining a versatile 8-bit CPU with In-System Programmable Flash on a monolithic chip, the Atmel AT89S51 is a powerful microcontroller which provides a highly-flexible and cost-effective solution to many embedded control applications. The AT89S51 provides the following standard features: 4K bytes of Flash, 128 bytes of RAM, 32 I/O lines, Watchdog...