This ppt deals with Digital meters,the digital components used in them,principle behind the working of Digital Voltmeter(DC) Digital Voltmeter(AC) and mechanism of Measurement of Current and Measurement of Resistance. Finally A complete DMM also the Measurement of hfe. A small project on constructing digital voltmeter and ohmmeter using Arduino.

1. Digital Voltmeter, Digital
Ammeter and Digital Multimeter
Done by,
C. Balaji 15E105
S. Deepak Arumugam 15E108
J. Karthickraja 15E117
S. Praveenkumar 15E137
Y. Elangovan 16E501
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2. Contents
 Advantages of Digital meters
 Digital Components
 Digital Voltmeter(DC)
 Digital Voltmeter(AC)
 Measurement of Current
 Measurement of Resistance
 A complete DMM
 Measurement of hfe
 A digital voltmeter and ohmmeter using
Arduino.
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3. Advantages of Digital meters
 Very high accuracy (5 to 0.05%)
 Has very input impedance (2MΩ)
which ensures less loading effect on
the input.
 The numeric display of digital meters
provide zero parallax error.
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4. Digital Components
 Crystal Oscillator
 Counter
 A/D Converter
 Voltage-Frequency Converter
 Phase Locked Loop
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5. Crystal Oscillator
 A piezoelectric crystal is used.
 Generally, a1MHz crystal is used
which produce a clock pulse of 1MHz.
 Used to provide the clock pulses.
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6. Counters
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7. A/D Converters
 Converts Analog data to Digital data
using a dual slope converter.
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8. Voltage-Frequency Converter
 Produces a frequency signal which is
proportional to the input voltage.
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9. Digital Voltmeter(DC)
 The voltage is first attenuated and
then converted into a digital word
which is displayed.
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10. Role of ADC
 The lines supplied by the ADC to the
display consists of
◦ The digital word
◦ A latch
◦ Start bit
◦ Polarity information
◦ Floating point information
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11. Features
 Polarity detection
 Auto ranging
 Auto zeroing
Polarity detection:
 The information is given by the ADC.
 When the voltage is +ve, the characteristic
curve of the converter is in first quadrant.
 The characteristic curve will be in the fourth
quadrant, if the voltage is –ve.
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12. Auto Ranging
 Two comparators are used.
 The typical ranges are,
◦ 0 to 100 mV
◦ 100 mV to 1 V
◦ 1 V to 100 V
◦ 100 V to 1000V
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13. Auto Zeroing
 Zero is displayed during the start of
conversion.
 This is achieved by discharging the
capacitance to the ground properly.
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14. DVM (AC)
 The AC is processed first i.e., phase
compensated attenuation with
rectification and filtering is done.
 The dc voltage obtained is converted
into a digital word, which is displayed.
 For high frequencies, a precision
diode with small reverse recovery time
is required.
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15. 15

16. DVM(Low voltage AC)
 For measurement of voltages in the
range between 1 nV and 10 nV, the
voltage is converted into a frequency
signal by a voltage-frequency
converter or phase locked loop.
 The frequency is measured by proper
networks.
 This reduces the effect of noise
through ADC.
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17. 17

18. Phase locked loop
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19. Measurement of current by DMM
 Typical ranges
◦ 0 to 10 mA
◦ 10 mA to 100 mA
◦ 100 mA to 1 A
◦ 1 A to 10 A
 Auto ranging is available.
 Auto zeroing is also available.
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20.  Two ways of measurement
◦ Measuring the voltage drop across a
resistance.
◦ Current frequency converter.
 In the first method, current is passed
through a constant resistance. The
voltage drop across it is measured
using a DVM.
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21.  In the second method, a current-
frequency converter is used.
 The output of comparator is a
frequency which is proportional to the
current.
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22. Measurement of Resistance using DMM
 A constant current is passed through
the unknown resistance and the drop
across it is measured by a DVM.
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23. Complete circuit of a DMM
The switches are coupled to each other.
The display is generally 3 digits (-1999 to 1999)
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24. Measuring hfe of a transistor
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25. Hfe measurement
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26. A small project: Digital Voltmeter
using ATMEGA328P
A0 GND
ATMEGA328P
Direct voltage measurement:
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27. RANGE EXTENDED VOLTMETER
A0 GND
ATMEGA328P
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28. CODE:
float voltage, previousvoltage=0;
void setup()
{
serial.begin(9600);
}
void loop()
{
voltage=analogRead(A0)*0.00488758553;
if(voltage!=previousvoltage)
{
Serial.println("the voltage is");
Serial.println(voltage);
previousvoltage=voltage;
}
delay(500);
}
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29. Ohmmeter using arduino
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30. Arduino code
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int analogPin= 0;
int a;
int Vin= 5;
float Vout= 0;
float R1= 1200;
float R2= 0;
float buffer= 0;
void setup()
{
Serial.begin(9600);
}
void loop()
{
a= analogRead(analogPin);
if(a)
{
buffer= a * Vin;
Serial.println(a);
delay(1000);
}
}

31. Challenges
 If you use a small value of known
resistance to measure a large value of
resistance the value gives up an error,
 So use known resistance which is
some what closer to the measuring
resistance to give an output with
greater accuracy.
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32. References
 Sawhney A K, “A Course in Electrical and
Electronic Measurement and Insrtumentation”,
Dhanapat Rai & Sons, New Delhi, 2011.
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33. Thank You!!
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