Summary of Digital voltmeter using ICL7107
This article describes a digital voltmeter using the ICL7107 3.5-digit ADC. It features high accuracy, low power consumption, and stable LED displays. The circuit converts analog voltage to digital via dual-slope integration, decodes it for seven-segment display, and allows range adjustment through resistor R4.
Parts used in the Digital Voltmeter using ICL7107:
- ICL7107 IC
- Resistor R2
- Capacitor C1
- Capacitor C2
- Resistor R4
- Seven segment displays
Description.
The circuit given here is of a very useful and accurate digital voltmeter with LED display using the ICL7107 from Intersil. The ICL7107 is a high performance, low power, 3.5 digit analog to digital converter. The IC includes internal circuitry for seven segment decoders, display drivers, reference voltage source and a clock. The power dissipation is less than 10mW and the display stability is very high.
The working of this electronic circuit is very simple. The voltage to be measured is converted into a digital equivalent by the ADC inside the IC and then this digital equivalent is decoded to the seven segment format and then displayed. The ADC used in ICL7107 is dual slope type ADC. The process taking place inside our ADC can be stated as follows. For a fixed period of time the voltage to be measured is integrated to obtain a ramp at the output of the integrator. Then a known reference voltage of opposite polarity is applied to the input of the integrator and allowed to ramp until the output of integrator becomes zero. The time taken for the negative slope to reach zero is measured in terms of the IC’s clock cycle and it will be proportional to the voltage under measurement. In simple words, the input voltage is compared to an internal reference voltage and the result is converted in a digital format.
The resistor R2 and C1 are used to set the frequency of IC’s internal clock. Capacitor C2 neutralizes the fluctuations in the internal reference voltage and increases the stability of the display.R4 controls the range of the voltmeter. Right most three displays are connected so that they can display all digits. The left most display is so connected that it can display only “1” and “-“.The pin5(representing the dot) is connected to ground only for the third display and its position needs to be changed when you change the range of the volt meter by altering R4. (R4=1.2K gives 0-20V range, R4=12K gives 0-200V range ).
For more detail: Digital voltmeter using ICL7107
- What is the function of the ICL7107 in this project?
The ICL7107 acts as a high-performance, low-power 3.5-digit analog-to-digital converter that includes internal decoders, drivers, and reference voltage. - How does the ADC process the input voltage?
The dual-slope ADC integrates the input voltage over a fixed time, then ramps down with a known reference voltage until zero, measuring the time against the clock cycle. - Can the voltmeter range be changed?
Yes, the range is controlled by altering resistor R4, such as using 1.2K for 0-20V or 12K for 0-200V. - What is the purpose of capacitor C2?
Capacitor C2 neutralizes fluctuations in the internal reference voltage to increase display stability. - Which pins are connected for the decimal point on the third display?
Pin 5, representing the dot, is connected to ground only for the third display. - What digits can the leftmost display show?
The leftmost display is configured to show only the digit "1" and the negative sign "-". - Does the decimal point position need adjustment?
Yes, the position of the decimal point must be changed when the voltmeter range is altered by changing R4. - What is the maximum power dissipation of the ICL7107?
The power dissipation is less than 10mW.
