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.
Features
- 3 ½ bit (0-1999) ADC module with 4-digit 7-segemnt display driver
- Supply Voltage: Single Supply 0-6V
- Dual Supply -15 to +15V
- 3 ½ ADC module
- Analog input voltage is equal to supply voltage
- Internal Oscillator is available
- Typical operating frequency : 48kHz
- Digital output value : 0 – 1999
- Can drive four 7-segment display
- Available in 40-pin PDIP, and MQFP
Where to use a ICL7107
The ICL7107 is an ADC module with a resolution of 3 ½ bit, meaning it can display digital value from 0-1999. The ADC used here is a dual slop ADC, so the applied voltage is compared with a reference voltage and then is approximated to find the applied voltage. The speciality of this IC is that it has an in-built 4-digit 7-segment display driver inside it. So to display the measured voltage, we simply have to hook up 7-segment display to the output of the IC and everything is ready. IT eliminates the need for MCU/MPU or programming.
The IC can measure voltages of maximum from -15V to +15V which is equal to the supply voltage. The digital output can vary from 0-1999 where each digit is displayed on a single 7-segment display. So if you are trying to measure voltage and display them on a 7-segment display without the use of MCU or programming, then this IC might be the right choice for you.
How to use ICL7107
Using ICL7107 is pretty straight forward, we just have to provide the reference voltage and set the internal clock for the ADC conversion to take place and we are all set. A basic sample circuit to measure voltage upto 200mV is shown below.
The IC has an internal clock which can be set using the pins 38, 39 and 40 by using a Resistor capacitor network. The formulae to calculate the set oscillator frequency is shown below; typically the value is set to 48 kHz
FOSC = 0.45/RC
Once the clock is set we have to provide the reference voltage for the ADC conversion to take place. The value of the measured analog voltage will then be displayed on the 7-segment display the increment of count can be calculated using the following formulae
The accuracy and the range of the measured voltage can be measured by using external circuits involving potential divider or op-amps but as always there is a trade off between the accuracy and range. You can refer the datasheet at the end of this page to know more technical details.
Applications
- Digital Voltmeter
- Digital Ammeter
- Instrument panel display
- Non-programmable applications
2D Model and Dimensions
