Digital Voltmeter using 8051 Microcontroller

Voltmeter is a measuring instrument, used to measure the voltage difference between two points in electrical network. Generally there are two types of voltmeters – one is analog voltmeter and the other one is digital voltmeter. In analog voltmeter a pointer moves on the scale to represent the voltage. Digital voltmeter directly displays the voltage in digits with the help of analog to digital converter. We have already seen the How to Design a Digital Voltmeter Circuit using ICL7107 in the earlier post. This article explains you how to design a digital voltmeter using 8051 microcontroller.This project measures the input voltage from 0V to 5V. Here, the input voltage should be DC voltage to get the accurate output on LCD. If you apply AC voltage as input, then will see the continuous running numbers on LCD as AC varies continuously.

Digital Voltmeter using 8051 Microcontroller Circuit Principle:

The major components in this project are 8051 microcontroller and ADC0804. In this project, we use analog to digital conversion process to display the voltage.

Also read the related post: How to Interface 16×2 LCD with 8051 Microcontroller?

Analog to Digital Conversion:

In real world, mostly we find analog data. To manipulate this data using digital systems, we need to convert analog data to digital, so that microprocessor or microcontroller is able understand and manipulate the data.

Interfacing of Physical Quantity to Digital System

1. Transducer: Transducer or sensor is used to convert the physical quantity to electrical energy. Light dependent resistor, temperature sensor, humidity sensor, gas sensor etc. are examples of transducers.
2. ADC (Analog to Digital Converter): ADC converts the input electrical voltage to Digital value.
3. Digital System: this system reads input digital data and displays the physical quantity on LCD for understanding purpose.

Here ADC IC generates the output digital value based on the input electrical voltage. The 8051 microcontroller reads this digital value and displays it on LCD.

Digital Voltmeter using 8051 Microcontroller Circuit Diagram:

Circuit Diagram of Digital Voltmeter using 8051 Microcontroller

Circuit Components:

• AT89C51 micro controller
• ADC0804 IC
• AT89C51 programming board
• Variable resistor
• adaptor or DC battery

  Digital Voltmeter Circuit Design using 8051 Microcontroller:

  In the above circuit, analog to digital converter IC data bits are connected to the PORT1 and control bits INTR, CS, WR, RD pins are connected to the P3.4, P3.5, P3.6, P3.7 respectively. LCD data pins are connected to the POTR2 of controller and control pins RS, RW, EN are connected to the P3.0, P3.1 and P3.2 respectively.
  ADC0804:  
  This is an 8 bit analog to digital converter. This IC uses successive approximation method to convert analog values to digital. It can take only one analog data as input. The step size of this IC is varied by varying the reference voltage at pin9. If this pin is not connected, VCC will be the reference voltage.
  For every 19.53mV, rise in input voltage the output is incremented by 1 value when the step size is at 5V. The conversion time of this IC depends on clock source.
  ADC Features:
  • 0 to 5V analog input voltage.
  • Built in clock generator.
  • Differential analog inputs.
  • Adjustable reference voltage.
  Below table shows the different step sizes for different reference voltages.
  In the above circuit diagram, pin9 (Vref/2) is left open so that input voltage span can be 0 to 5V.
  Step size = Vref/(2 pow(n))
  Where n is resolution. For ADC0804 the resolution n=8. The digital output can be calculated using the formulae
  Dout = Vin/stepsize.
  Vin – analog input voltage
   For example, let the analog input voltage is 4V, then the digital output is Dout=4/19.53mV=204.

  How Digital Voltmeter Circuit Works using 8051 Microcontroller?

  1. Initially burn the program to the at89c51 microcontroller.
  2. Now give the connections as per the circuit diagram.
  3. Connect variable resistor at the input of probes to vary the input analog input voltage.
  4. make sure that maximum analog input voltage should be less than 5V DC
  5. Connect a digital multi meter at the Pot to measure the input voltage.
  6. Now switch on the board supply.
  7. Now observe both LCD and digital multi meter, both displays the same voltage.
  8. Slowly increase the analog input voltage by varying the pot, now you can observe that both multimeter and LCD displays the same voltages so that we can say that voltmeter is working properly.
  9. Switch of the board supply.

  Digital Voltmeter Circuit Applications:

  • This system is used to measure the voltage in low voltage applications.
  • Used to measure the toy batteries.
  • We can measure the physical quantities like temperature, humidity, gas etc. using this system with a little modification.

  Digital Voltmeter Circuit Limitations:

  • The input analog voltage range should be 0 to 5V.
  • Using this system we can measure only one analog input value at a time.

  rd = 0;                                   //Make RD low
  adc = adc_port;              //Read ADC port
  rd = 1;