# ICL7106 / ICL7107 Digital Meter Design

The ICL7106 and ICL7107 are single chip digital meter solutions by the Intersil Corporation. This is an extremely useful integrated circuit (IC) used in education and industry. In education, it allows a student to build his or her own measuring instrument, whilst keeping the cost of the build to a reasonable level. This IC requires a display, and a handful of commonly available low-cost components to make a digital meter.

I love electronic measuring instruments, and am a collector of digital and analogue meters. With age creeping up, it is annoying to have to wear reading glasses just to read the meter. Therefore, I decided to build my own meter with a large LED display.

I chose the ICL7107 chip because it can directly drive a seven-segment LED display and my intention was to use the largest brightest display that I could find. The ICL7106 is an identical IC however; it drives a liquid crystal display (LCD) panel.

I did not want to simply construct a meter but also wanted to follow the design principles and some of the mathematics that are involved. I have made this article as simple as possible for anyone to follow to make his or her own meter.

This article will take you through some of the mathematics of choosing the component values, some of the design principles involved, as I understood them, and the design ideas to build a simple meter.

The meter design is in the “Schematic” section, as I decided to make it an interactive schematic so that when you click on the component, a link takes you to the relevant page where my reasons for choosing the component values are given. However, these component values are very much the optimum values recommended in the datasheet.

As it turned out, building a meter around this IC was simpler than I thought because all the optimum values for the components have been calculated for you for either a 200 mV or 2 V full-scale options. All you would need to do is to connect a selector switch and some resistors to make a multi-meter.

Originally, I wanted to build just the evaluation circuit that is described in the AN023 Application Note datasheet but I could not get anyone to sell me the kit at an affordable price, hence I decided to make it anyway by buying all the components separately. I was able to buy the IC for three pounds on eBay, which brought it within financial reach.

After studying the circuit, I realised it needed just a few more components to turn it into a multi-range voltmeter. We engineers always race forward with imagination, and before you know it, it will be inside a large box with switches and lights somewhat similar to the control panel on the USS Enterprise, measuring the phase variance of the warp coils of course.