ICL7106 Analog-to-Digital Converter with Meter Circuit

One of the most important tools in electronics is an accurate and reliable meter. Nowadays, we use digital meters because they are precise, easy to use, and relatively inexpensive. So today, we will learn about the ICL7106 3½ digit A/D converter with LCD Driver and use it to build a digital meter.

The ICL7106 is designed as an integrated circuit for digital meter applications. We will be using it to build a digital voltmeter and ammeter with two starting measurement ranges: 0 to 200mV, which is enough to replace the analog millivolt and milliamp meter that we have been using.

A few examples of usages for the ICL7106 include replacing the analog meter in circuits such as a frequency meter, temperature reader, moisture meter, light meter, and many more.

Even though precision may be lower than that of a store-bought multimeter, this circuit will still be much more precise than an analog meter. It would also have an LCD reading and a very high input impedance within its measurement ranges.

The ICL7106 3½ A/D Converter with LCD Driver

The ICL7106 is a low-power 3½-digit analog-to-digital converter together with an integrated display driver, a clock, and a reference. It can be connected directly and drive an LCD measurement reading display. The ICL7106 is often the choice for a single-chip digital meter solution.

Features

• Maximum zero drift of 1μV per °C
• Zero reading for 0V input within 10pV
• Noise level lower than 15μVp-p
• Usual input current of 1pA
• Power dissipation of less than 10mW
• Differential input and reference
• Can directly drive an LCD
• Integrated clock and reference
• Typical meter applications require only basic components

Pinouts

Pinouts of the ICL7106 A/D Converter

Digital Meter Circuit using the ICL7106

Our plan for this ICL7106 digital meter circuit is to use it to replace an analog display in circuits such as this frequency meter and moisture meter. Because, as mentioned above, it will have higher precision than the analog solutions. 

Therefore, this circuit will only measure in the 0-200mV range. However, you could make a few changes to this circuit and increase the range to 0-2V as well. We will also show you other ways to widen the measurement range and increase the number of them.

Using this Circuit

We built this prototype of the ICL7106 digital meter circuit, and after testing, it worked very well. We have tried replacing the analog meter with it; the reading is more accurate, and the number range displayed on the LCD is 0-199. This circuit helps improve the readability of a temperature or moisture meter by displaying the exact values on the LCD.

In this prototype circuit, we set the range to 0-200mV. So we use VR1 to set the reference voltage—read from REF HI and ground—to exactly 100mV.

Increasing the Measurement Ranges

To increase the measurement ranges, we would need to add resistors across the input of the circuit (Vin+ and Vin-). There are two ways of doing it, depending on the applications.

• Increasing Voltage Ranges
• Convert to Digital Ammeter 

Conclusion

From our testing, the ICL7106 is quite effective and precise, similar to the ICL7107. It uses just a single 9V battery as a power source. The circuit also consumes very little power overall due to the LCD. The ICL7106 error rate is about 2-3% compared to the analog meter at around 10%, and its low input impedance allows it to measure very low currents. Anyhow, in our opinion, this chip is still quite expensive. In the future, we will find a better alternative for this chip.

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