With a single IC L 7107, you can make a 4 digit voltmeter that can show 0-2000 voltsthrough seven segment display. The circuit is low component one and the reading is reliable and accurate. This circuit is used in digital panel meters to give alpha numerical display.
The whole circuit is built around a single 40 pin IC L 7107.It is an Analogue to Digital Converter (ADC) IC from Intersil. The whole circuits for converting analogue signals to digital signals and the seven segment display driver circuit are enclosed in the package of IC. The circuits inside the IC are AD converter, a comparator, a clock, a decoder and a display driver. The IC works in 5 volt dual power supply and consumes less than 200 mA current and shows an accuracy of 0.1 %. The IC is CMOS and is very sensitive to static electricity. It comes wrapped in aluminium foil to protect it from static discharges and it should be handled with great care to avoid damaging it. Try to avoid touching its pins and keep the circuit and the body at ground potential while inserting it in IC base.
The ADC is generally known as Dual Slope converter or Integrating Converter and is immune to noise. The ADC works in two stages:
1. Stage 1- During the stage 1, the input voltage given in the integrator which gives a voltage proportional to the input voltage. The integrator is fed with an internal reference voltage and the output of the circuit reduces until it reaches a zero reference voltage.
2. Stage 2 – This stage is the Negative Slope period which depends on the output from the integrator. As the duration of stage 1 is fixed, the length of the stage 2 is variable making possible to compare the input voltage with the fixed reference voltage. The result of this comparison is then coded and send to the decoder and then to the display driver.