Introduction

In any electronics workshop, being able to measure voltage accurately is crucial for diagnosing and debugging circuits. One of the essential tools in this regard is a digital voltmeter, which allows you to measure the voltage in a circuit with precision. In this project, we’ll build a simple but effective digital voltmeter using the 391077-01, a common seven-segment display driver IC.

The 391077-01 is a component that helps drive seven-segment displays, which are widely used for displaying numerical values in digital form. By combining the 391077-01 with a few additional components, such as an analog-to-digital converter (ADC), microcontroller, and a seven-segment display, we will create a voltmeter that can measure and display DC voltages in real-time.

This project will provide hands-on experience in working with digital displays, ADCs, and basic microcontroller interfacing. By the end of this tutorial, you'll have a fully functional digital voltmeter to use in your own electronics projects, with clear numerical readings of the voltage in your circuits.

Materials Needed

To build this digital voltmeter, you'll need the following components:

● 391077-01 Seven-Segment Display Driver IC

● Seven-Segment Displays (at least two, for a two-digit voltmeter)

● Microcontroller (such as an Arduino, ESP32, or any other microcontroller with ADC capability)

● Analog-to-Digital Converter (ADC) (if using a microcontroller without an integrated ADC)

● Resistors (for current-limiting on the seven-segment displays)

● Capacitors (for noise reduction and voltage stabilization)

● Voltage Reference Source (to ensure accurate measurements)

● Breadboard and Jumper Wires (for easy circuit assembly)

● External Power Supply (for the microcontroller and the voltmeter)

Step 1: Understanding the 391077-01

The 391077-01 is an integrated circuit designed specifically to drive seven-segment displays. Seven-segment displays are a popular way to show numerical values in digital form, and the 391077-01 provides an easy way to interface with them.

Here’s how the 391077-01 works:

● It is a BCD (Binary Coded Decimal) to seven-segment display driver, meaning it takes a 4-bit binary input (representing digits 0-9) and converts that into the necessary signals to light up the appropriate segments of the seven-segment display.

● The IC drives the segments of the display through its output pins. Each output pin corresponds to one of the segments (A to G) of the seven-segment display. By providing the right combination of HIGH and LOW signals to these pins, the IC lights up the necessary segments to form numbers 0 through 9.

● The 391077-01 is designed to work with common anode or common cathode seven-segment displays and can drive two digits simultaneously (for a two-digit voltmeter).

In this project, we will use the 391077-01 to drive the seven-segment displays and will send the numerical voltage readings from the microcontroller to the IC, which will display the voltage on the displays.

Step 2: Circuit Design

Now that we understand the key component, let’s break down the circuit for our digital voltmeter.

1. Powering the Circuit

● The microcontroller will be powered by a 5V supply, which can come from a regulated USB power source or a dedicated power adapter. The 391077-01 and the seven-segment displays will also be powered by this 5V supply.

● Make sure that all components share a common ground to ensure proper operation and signal integrity.

2. Microcontroller and ADC Setup

To measure voltage, we will need an analog-to-digital converter (ADC). The microcontroller (e.g., Arduino) typically has a built-in ADC that allows you to read analog voltages from an input pin.

● Choose an analog input pin on the microcontroller (e.g., A0 on Arduino) and connect it to the input voltage you wish to measure. The voltage range should be within the ADC’s range (typically 0-5V for Arduino).

● Use a voltage divider if necessary to scale down the input voltage to fit within the ADC range. For example, if you're measuring voltages above 5V, you may need to divide the voltage using resistors to bring it down to a measurable range.

3. Connecting the 391077-01 Driver IC

The 391077-01 has four input pins (B, C, D, and E) that accept a 4-bit binary value (BCD) corresponding to the digits 0-9. The IC then controls the segments of the connected seven-segment display based on the BCD value.

● BCD Inputs (Pins B, C, D, and E): These will be connected to four output pins from the microcontroller. The microcontroller will send the digit (0-9) to the 391077-01 as a binary value, and the IC will convert this to the appropriate segments of the seven-segment displays.

● Output Pins (Segments A to G): These will be connected to the seven-segment display. Each pin corresponds to one of the segments (A to G) that light up to display the numbers.

● Common Pin: Depending on whether you're using a common anode or common cathode display, you will either connect the common pin to ground or positive voltage.

4. Seven-Segment Displays

● You will need at least two seven-segment displays for a two-digit voltmeter.

● Connect the segment pins (A to G) from the 391077-01 to the corresponding pins on the displays.

● Use resistors (typically 330Ω to 1kΩ) in series with the segment pins to limit the current and protect the displays from excessive current.

Step 3: Assembly of the Circuit

Once we have the design, we can proceed with building the circuit.

1. Place Components on a Breadboard

Start by placing the microcontroller (e.g., Arduino) on the breadboard, ensuring that it is powered properly. Next, place the 391077-01 IC and the seven-segment displays on the breadboard. Make sure there’s enough space for the wiring and the connections.

2. Connect Power Rails

● Connect the 5V rail to the Vcc pins of the microcontroller, the 391077-01, and the seven-segment displays.

● Connect the ground rail to the GND pins of all components.

3. Wiring the BCD Inputs

● Connect four pins from the microcontroller to the BCD input pins (Pins B, C, D, and E) on the 391077-01 IC. These pins will send the 4-bit binary values representing the digits to be displayed on the seven-segment displays.

4. Connecting the Seven-Segment Displays

● Connect the segment pins (A to G) of the 391077-01 to the corresponding pins of the seven-segment displays. Use current-limiting resistors to protect the LEDs in the displays.

5. Voltage Measurement Input

● Connect the analog input pin (e.g., A0 on Arduino) to the voltage source you want to measure.

● Use a voltage divider if necessary to ensure the input voltage is within the ADC’s measurable range.

Step 4: Programming the Microcontroller

Once the circuit is assembled, it’s time to write the program that will control the voltmeter.

1. Reading the Voltage

The microcontroller will continuously read the input voltage using the ADC. It will convert the analog voltage into a digital value corresponding to the measured voltage.

● For example, if you are using an Arduino, you can use the analogRead() function to read the voltage on the input pin.

2. Converting the ADC Value to a Displayable Format

The ADC value (which ranges from 0 to 1023 for a 10-bit ADC) will be proportional to the input voltage. You will need to scale this value to display the voltage in a human-readable format on the seven-segment displays.

3. Sending the Data to the 391077-01

Once the voltage is calculated, the microcontroller will split the value into tens and ones digits and send the appropriate binary data to the BCD inputs of the 391077-01. The 391077-01 will then display the corresponding digits on the two seven-segment displays.

Step 5: Testing and Calibration

After programming the microcontroller, power on the circuit and test the digital voltmeter by applying known voltages to the input. Ensure that the voltage is correctly displayed on the seven-segment displays.

● Use a known voltage reference source for calibration, ensuring that the voltage readings are accurate. Adjust the program if necessary to match the correct voltage readings.

Conclusion

Building a digital voltmeter using the 391077-01 driver IC is a fun and educational project that teaches you how to work with seven-segment displays, analog-to-digital conversion, and microcontroller programming. This project provides a hands-on way to measure and display voltages in real-time, making it a useful tool for your electronics bench.

By following the steps in this project, you’ve learned how to interface with the 391077-01, how to use the ADC to measure voltages, and how to display numerical values using a seven-segment display. You can further expand this project by adding more features, such as voltage range selection or even using it to measure AC voltages with the proper circuitry.

This simple voltmeter can now serve as a practical tool in your electronics toolkit, providing you with accurate voltage measurements for various projects and applications.