How To Drive A 7-segment Display - The Learning Circuit

Summary

In this educational video, the host teaches viewers how to drive a seven-segment display using a BCD to seven-segment decoder. The tutorial covers the basics of seven-segment displays, including common anode and cathode configurations, and the use of a BCD decoder to translate binary to control LED segments. The practical demonstration involves connecting the decoder to switches for input and LEDs for indicator lights, with a focus on understanding the decoder's pin functions and wiring the circuit correctly. The video encourages learning about electronic components and invites viewers to share their projects on the element14 community.

Takeaways

• 😀 The video is about driving a seven-segment display using a BCD to seven-segment decoder.
• 🔢 Seven-segment displays are commonly used in technology to display numbers and consist of seven LED segments that can be lit up in various combinations.
• 🌐 The script mentions element14.com as a community for engineers to connect and collaborate.
• 🔌 There are two types of seven-segment displays: common anode, where all anodes are connected together, and common cathode, where all cathodes are connected.
• 🛠️ The LS447 is a seven-segment decoder used in the video to convert four-digit binary (BCD) into signals for the display segments.
• 📚 Understanding the decoder's logic can be achieved by reviewing the datasheet and logic diagram, which are complex and not detailed in the video.
• 🔩 The decoder chip has 16 pins with specific functions, including BCD inputs (A, B, C, D) and segment outputs (a-g).
• 🔑 The video demonstrates building a circuit with switches and LEDs to manually input BCD numbers and visualize them on the display.
• 💡 The display has an extra pin for the decimal point, which is also an LED and requires a current-limiting resistor.
• 🔌 Additional pins on the decoder, such as LT (Lamp Test), RBI (Ripple Blink Input), and BI (Blinking Input), have specific functions that are explained in the video.
• 🔄 The video concludes with a call to action for viewers to share projects involving multiplexers, demultiplexers, encoders, and decoders on the element14 community.

Q & A

What is the purpose of the element14 electronics community?

The element14 electronics community is a platform where top engineers from around the world can connect and collaborate.

What type of display is being discussed in the video?

The video discusses a seven-segment display.

Where might you have seen a seven-segment display before?

You may have seen a seven-segment display in alarm clocks, radios, or other pieces of technology that display numbers.

How are the segments of a seven-segment display controlled?

Each LED-lit segment of a seven-segment display is controlled by a separate pin.

What is the function of the extra pin labeled 'DP' on the seven-segment display?

The 'DP' pin controls the decimal point on the display.

What are the two types of seven-segment displays mentioned, and how are they different?

The two types of seven-segment displays are common anode and common cathode. In common anode displays, all the anodes are connected together, while in common cathode displays, all the cathodes are connected together.

What type of decoder is used in the video to drive the seven-segment display?

The video uses a BCD to seven-segment decoder, specifically the 74LS47 decoder.

What does BCD stand for, and what does it represent?

BCD stands for Binary Coded Decimal, which is a four-digit version of binary that represents decimal numbers.

How does the decoder translate BCD to control the seven-segment display?

The decoder translates four-digit binary input (BCD) into seven output signals that control the LED segments of the display.

How are the inputs and outputs of the 74LS47 decoder connected in the circuit?

The inputs (A, B, C, D) are connected to switches to manually input the BCD number. The outputs (a, b, c, d, e, f, g) are connected to the corresponding pins on the seven-segment display.

What additional components are used in the circuit to ensure proper operation of the LEDs?

Current limiting resistors are added to each LED segment to prevent excessive current and protect the LEDs.

What are the functions of pins 3, 4, and 5 on the 74LS47 decoder?

Pin 3 (LT) is for lamp test, pin 4 (BI/RBO) is for blanking input and ripple-blanking output, and pin 5 (RBI) is for ripple-blanking input.

How are the active low pins on the decoder handled in the circuit?

The active low pins (LT, BI/RBO, RBI) are connected to the supply voltage using a 1 kilo ohm resistor to keep them inactive.

What are the power supply connections for the seven-segment display and the 74LS47 decoder?

The common anode display's pins 3 and 8 are connected to the supply voltage, while the decoder's pin 16 is connected to the positive supply voltage and pin 8 to ground.

How can you test the functionality of the seven-segment display?

You can use the lamp test (LT) pin, which when pulled low, will turn on all segments of the display.

What might be a more common method to send input signals to the seven-segment display in practical applications?

In practical applications, a microcontroller is often used to send input signals instead of manual switches.

Where can viewers share their projects that incorporate the discussed ICs?

Viewers can share their projects on the element14 community at element14.com/thelearningcircuit.

Outlines

00:00

😀 Introduction to Seven Segment Display with BCD Decoder

This paragraph introduces the topic of driving a seven segment display using a BCD to seven-segment decoder. It explains the purpose of the seven segment display, which is commonly found in devices like alarm clocks and radios to display numbers. The display consists of seven individual LED segments that can be controlled by separate pins. The script also discusses the difference between common anode and common cathode displays, and the choice of using a common anode display with a BCD decoder. The decoder's function is to translate four-digit binary (BCD) into signals that control the LED segments, with a brief mention of the complexity of the logic diagram and the need to refer to the datasheet for a deeper understanding.

05:00

🛠️ Circuit Assembly and Pin Configuration for BCD Decoder

This paragraph delves into the practical aspects of assembling the circuit for the BCD to seven-segment decoder. It describes the pin configuration of the decoder chip, including the input pins for the BCD digits (A, B, C, D) and the output pins for the seven segments (a through g). The script outlines the process of connecting switches and LEDs to input the BCD numbers, with the inclusion of current-limiting resistors for safety. It also explains the need to connect the remaining pins of the display and decoder to avoid floating pins, such as connecting the decimal point LED to ground and the anodes to the supply voltage. Additionally, the paragraph covers the functions of the LT (Lamp Test), RBI (Ripple Blinking Input), and BI (Blinking Input) pins, and how to keep them inactive using pull-up resistors.

Keywords

💡Seven Segment Display

A seven segment display is an electronic display device used to show decimal numerals and, in some cases, letters. It consists of seven LEDs or other light sources arranged in a specific pattern to represent the digits 0-9. In the video, the concept is central as the tutorial focuses on how to drive such a display using a BCD to seven-segment decoder, with examples of how different segments light up to form numbers.

💡BCD to Seven-Segment Decoder

BCD stands for Binary Coded Decimal, a system used to represent decimal digits in a binary form. The BCD to Seven-Segment Decoder is an integrated circuit that translates the BCD input into signals that control the lighting of the segments in a seven segment display. The script explains that this decoder is essential for converting the binary representation of numbers into a visual display on the seven segment display.

💡Common Anode

In the context of the video, a common anode display refers to a type of seven segment display where all the anodes of the LEDs are connected together. This configuration requires the use of a decoder that can drive the anodes with a common connection, as opposed to a common cathode display where the cathodes are connected together. The script mentions choosing a common anode display for the tutorial.

💡LED

LED stands for Light Emitting Diode, a semiconductor device that emits light when an electric current passes through it. In the script, LEDs are the light sources used in the seven segment display, with each segment being an individual LED that can be controlled to display different numbers.

💡Anode

The anode in electronics is the electrode through which conventional current enters a polarized electrical device. In the context of the seven segment display, the anode is the positive terminal of the LED that needs to be connected to the power supply to light up the segment.

💡Cathode

The cathode is the electrode from which conventional current leaves a polarized electrical device. In the script, it is mentioned in the context of common cathode seven segment displays, where all the cathodes are connected together and controlled separately from the anodes.

💡BCD Input

BCD Input refers to the input of a four-digit binary number that represents a decimal digit. The script explains that the decoder requires this input to function properly and display the correct number on the seven segment display.

💡Pin Configuration

Pin configuration in the script refers to the specific arrangement and function of the pins on the BCD to seven-segment decoder chip. The video describes the purpose of each pin, such as the BCD input pins labeled A, B, C, and D, and the output pins labeled a through g for the seven segments of the display.

💡Current Limiting Resistors

Current limiting resistors are used in circuits to limit the amount of current that flows through a component, in this case, the LEDs in the seven segment display. The script mentions the importance of including these resistors to prevent damage to the LEDs and ensure they operate correctly.

💡Lamp Test (LT) Pin

The Lamp Test (LT) pin on the decoder is used to test the functionality of the seven segment display. When this pin is low, all segments of the display will light up. The script explains that this feature is useful for checking if the display and decoder are working correctly.

💡Ripple Blinking

Ripple blinking is a feature that allows the LEDs in the seven segment display to blink in a sequential manner. The script describes the use of a specific pin on the decoder to enable this feature, creating a visual effect that can be used for various applications.

Highlights

Introduction to driving a seven-segment display using a BCD to seven-segment decoder.

Explanation of what a seven-segment display is and its common applications.

Description of the individual LED segments in a seven-segment display and how they are controlled.

Differentiation between common anode and common cathode seven-segment displays.

Introduction of the LS447 BCD to seven-segment decoder as the driving chip.

Explanation of how BCD (binary coded decimal) is converted to control seven-segment displays.

Pinout details of the LS447 decoder, including input and output pins.

Use of switches to manually input BCD numbers for the demonstration.

Inclusion of indicator LEDs with switches to visualize BCD inputs.

Importance of current-limiting resistors for LED safety.

Connection details for the seven segment pins to the display.

Handling of the decimal point LED on the seven-segment display.

Connection of supply voltage to anodes for a common anode display.

Details on the additional pins of the decoder, including LT, RBI, and their functions.

Use of 1 kilo ohm resistors to keep certain decoder pins inactive.

Assembly of the electronic circuit with the described components.

Suggestion to use a microcontroller for more advanced applications.

Invitation to share projects involving multiplexers, demultiplexers, encoders, and decoders on the element14 community.

Transcripts

the following program is brought to you

by element14 the electronics community

where you can connect and collaborate

with top engineers from around the world

join now at element14.com slash presents

hi and welcome back to the learning

circuit today we're going to learn how

to drive a seven segment display using a

BCD to seven-segment decoder this is a

seven segment display you may have seen

one in an alarm clock a radio or some

other piece of technology that's been

around for a while that needs to display

numbers seven segment displays contain

leds that light up seven individual

segments numbers can be displayed by

changing which segments are on and which

are off each LED lit segment is

controlled by a separate pin you may

notice this display has an extra eight

pin labeled D P that control is the

decimal point in this display all the

anodes are connected together making

this a common anode display there are

also common cathode seven segment

displays where the LEDs are flipped with

the cathodes all connected and the

anodes going to the individual segment

pins I chose to use a common anode seven

segment display so I'm using a seven for

LS four seven decoder as a driver in the

last episode we discussed how BCD is

converted to seven segments BCD is

binary coded decimal a four digit

version of binary so this type of

decoder translates four digit binary to

seven signals that control the LED

segments of the display so if we want to

display a two we input a four digit

binary two into the decoder and an

output signals that turn on the

appropriate segments to display a two if

you want to try to understand how the

decoder works more in-depth take a look

at the datasheet and try to decipher the

logic diagram it's pretty complex so I'm

not going to take the time to get into

it right now so we know our chip needs

at least four signal inputs the

four-digit BCD number and at least seven

outputs one for each of the LED lit

segments let's take a look at the pin

out for our decoder to find them our

chip has 16 pins

we're used to seeing VCC our supply

voltage and ground on the left you can

see pins seven one two and six are

labeled a b c and d those are for the b

c d input one pin for each of the four

digits on the right you can see that

pins 9 through 15 are labeled lowercase

a through g these are the seven outputs

one for each segment of our display well

getting two pins three four and five

later for our circuit

we'll use four switches to manually

input the BCD number if we look at the

function table for our decoder we can

see that the inputs need to go high to

send a signal you can see that when a is

high and B C and D are low it sends a

decimal number one so we want the supply

voltage going through our switches to

those input pins for funsies

we'll add an LED to each switch as an

indicator light so we know when it's on

and to help visualize our BCD numbers

and we'll be sure to throw in some

current limiting resistors to keep our

LEDs happy the LED anodes connect to the

supply voltage through the switches and

to ground through the resistors we'll

connect each switch LED combo up to the

correct input pin on the decoder ABCD

going right to left so we can input our

BCD numbers on the output side of our

decoder

we'll need each of the seven segment

pins to connect to the corresponding pin

on the display as we know our display is

made with LEDs so once again we'll add

current limiting resistors one for each

LED lit segment okay

our main signal inputs and outputs are

taken care of let's take a look at the

rest of the pins to see what we still

need to do our display still has three

pins open 3 5 and 8 this display has an

extra led for the decimal place pin 5

you don't ever want to leave pins

floating meaning unconnected so we'll

connect it to ground so it's always on

and since it's also an LED we'll use

another current limiting resistor we're

using a common anode display and as

usual anodes are connected to power

positive so pins 3 & 8 need to be

connected to the supply voltage okay

that's it for our display now back to

our decoder pin 16 is VCC

see so we'll connect that to positive on

our power supply and pin eight is ground

so we'll connect that to ground

that leaves pins three four and five pin

three LT is a lamp or light test it lets

you test the display if this pin is low

all segments LEDs will turn on pin five

is a ripple blinking input if this pin

plus the four inputs are low while LT is

high all segments are off pin four has

two functions the first blinking input

is active low so when this pin is low

all segments are off no matter the

status of the inputs the second function

ripple blinking output is to provide a

low level if inputs a through D and RBI

are at low level while LT is at high

level all of these pins are active low

so we want to pull them high to keep

them inactive so we'll connect them to

the supply voltage using a 1 kilo ohm

resistor ok that's everything let's put

this thing together electronics assemble

[Music]

now more commonly with this circuit you

would probably use a microcontroller to

send your input signals in place of the

four switches now I did this project to

show how a decoder works because in the

last episode I talked about multiplexers

demultiplexers encoders and decoders now

if you've got a project that

incorporates one of those four ICS I

would love to see it please post about

them on the element14 community on

element14.com board / the learning

circuit and happy learning

[Music]