Interfacing 7-segment display using 7447 decoder

Monday, August 17th, 2009

The Light Emitting Diode (LED), finds its place in many applications in this modern electronic fields. One of them is the Seven Segment Display. Seven-segment displays contains the arrangement of the LEDs in “Eight” (8) passion, and a Dot (.) with a common electrode, lead (Anode or Cathode). The purpose of arranging it in that passion is that we can make any number out of that by switching ON and OFF the particular LED’s. Here is the block diagram of the Seven Segment LED arrangement.

Pin configuration of a seven segment display:
7 segment pin configuration

LED’s are basically of two types:

  1. Common Cathode (CC)
    All the 8 anode legs uses only one cathode, which is common.
  2. Common Anode (CA)
    The common leg for all the cathode is of Anode type.

For the discussion purpose, we use CC LED, where by just reversing the logical voltages we can implement the same for CA LED also.

In a CC LED, all the 8 legs (‘a’ through ‘h’) are of anode type and the common cathode will be connected to the GND of the supply. By energizing any of the legs with +5 Volts will lead to switch the correspondent segment ON. In the microprocessor binary system, 0Volts will be considered as Binary 0, and 5Volts will be considered as Binary1. Considering these two condition, we can make an arrangement as the microcontroller gives OUT the 0s and 1s through its ports, which is connected to the 8 legs of the LED. Of course, we can control the Port Output; implicitly we can Switch-ON required legs of the display.

There 2 methods of interfacing LED with the Microcontroller Intel 8051/8951.

  1. Using lookup table. This uses 7 output pins of microcontroller
  2. Using 7447 decoder. This method uses 4 output pins of microcontroller

The difference between the two main methods is simple and clear. In both the cases, microcontroller communicates with external world through its ports. But, in the 1st case, we connect all the 8 pins of the port directly to the LED and control the voltage through the ports manually to display the desired number. But, in the second case, we send the BCD of the number that we wanted to display to a middleware IC 7447, the BCD to LED code converter, which by itself gives out the correspondent 7 segment codes to the LED.

Here we explain using lookup table. Click here for the method “using 7447 decoder”

Using 7447 decoder:

The IC7447 is a BCD to 7-segment pattern converter. This setup is the advanced form of the <previous> setup where we entered the patterns manually to display the desired character. Here in this case, the IC7447 takes the Binary Coded Decimal (BCD) as the input and outputs the relevant 7 segment code. We connect first four pins of the microcontroller Port 2  to the 7447 and the Output 8 pins of 7447 to the 8 legs of the LED as shown in the figure. Te circuit diagrams are shown below, the first figure is interfacing the CA LED where as the second is of CC LED. The number required to display is sent as the lower nibble of the Port 2 of the Microcontroller. The 7447 converts the four input bits (BCD) to their corresponding 7-segment codes. The outputs of the 7447 are connected to the 7-segment display.

Circuit diagram for interfacing Common Anode 7-Segment Display

Circuit diagram for interfacing Common Anode 7-Segment Display

Circuit diagram for Common Cathode 7-Segment Display

Circuit diagram for Common Cathode 7-Segment Display


This program displays characters 0 through 9 on seven-segment display 
using IC 7447 as the middle wear.
  again: mov a,#00h                  ; Start form zero
     up:  mov p2, a                  ; Move to Port 2
          mov r3,#255                ; Delay
     D1:  mov r1,#255
      D:  djnz r1,D
          djnz r3,D1
          inc a
          cjne a,#0ah,up
          sjmp again

Author Name :

Total : 50 Comments

50 Responses to “Interfacing 7-segment display using 7447 decoder”

  1. manaquitos says:

    how about the config of ic 555 in 7 segment diagram?????

  2. Gray says:

    Are all 7 segment displays pinned out this way, the same LEDs to the same pins?

  3. syasya says:

    why was 330ohm resistor included ??

  4. Ranajeet says:

    I requied to Implement SSD with IC 7448.How do I?

  5. Tariq says:

    if i use two 7447 ic’s having 2 common cathode and also apply 3 simple switches functions of switches are up,down and on/off …. then what’s the procedure of coding ? i want interface it with parallel port ….

    i need it in urgent , do help me !!

  6. Tintumon says:

    Whether it works with out using controller, I jut want it to
    work by simply supplying power through driver. wht to do?

  7. I want to know more about making led seven segment using c .

  8. abhishek says:

    Can 7447 drive Common Cathode display also as shown above.
    I think 7448 is used.Please clarify.

  9. amar says:

    in case of common cathode display only difference being that coommn cathode terminal is connected to ground through 330 ohms bleeder and remaining circuit remains the same…

  10. Genuinely truly excellent web site submit which has obtained me considering. I in no way looked at this from the stage of look at.

  11. sujeet singh HRIT ghaziabad says:

    why we use 8951 micro controller if we are using only one segment of
    display.we can easily give 1 or 0 to input of Binary to seven segment decoder ic can also given by switches which toggle from 0 to 1 or 1 to 0.
    simple why we make circuit complicated .Engineers means design the best circuit
    in cheapest price and user friendly.

    if you know anything else contact me my email
    id is
    i am from HRIT ghaziabad uttar pradesh India

  12. milan says:

    in the 7447 RBI and RBO, what indicate???

  13. sneha says:

    why we use 8951 micro controller if we are using only one segment of
    display.we can easily give 1 or 0 to input of Binary to seven segment decoder ic can also given by switches which toggle from 0 to 1 or 1 to 0.
    and i think we can use ic 7448….pls clarify
    my id is

  14. sundresh says:

    how to configure 7 seg dip. by using 74147 and 7447

  15. pankaj says:

    how to make it?

  16. ^_^ says:

    if i were to use an external gate to make some changes in the display,where should i put it???is it on the input??or output???

  17. yag1 says:

    Im new to this 7-segment display i want to ask some questions..
    how to interface a micro-controller to a multiple seven segment display?
    say 10 7-segment display? do i have to use latches and decoder/multiplexer
    for this? hoping for your king reply…

  18. raksha singh says:

    can any one help me with what kind of seven segment display i use which is compatible with msp430f2122 can mail me on

  19. jonna tiglao says:

    can you help me of seven segment

  20. taufikatyn says:

    can change 7447 to 7448??

  21. Soundar Pandian says:

    Using 7 output how can configure the seven segment display with 24VDC to PLC.

  22. safer says:

    Please give m a circuit for football substitute board using 89c51&7447

  23. ezeldeen says:

    how can I use decoder with display

  24. banish gupta says:

    thanx bro.. Ur info help me a lot.. Plz send me request on fb. i want to get more knowledge from u..:-)

  25. Pradeep says:

    How to recognise7-Segment Display is common cathode or common anode.

  26. eiram lee says:

    Hello there, do you have codes or program aside from the one given above?…specifically using c++

  27. Gaurav says:

    Hello there, I want to make an circuit with using Opam to perform addtion of two voltage signal….which should be displayed on double seven segment display… between these..i used simply encoder and Bcd but im unable to display the result as per according to my circuit…………please help me………or send me a corect circuit for it……. that’s my email id…………please send me that correct circuit…

  28. Gaurav says:

    Im in final year………so, please suggest me an advance project for my final year which should be based on micro controller…………………that’s my email id…………..

  29. sumeet says:

    i want to make a digital clock with 3 displays of hours minutes and seconds using 8051 uc & 7 segment displays….so can u please tell me how to interface six seven segments with the microcontroller for this purpose?

  30. furqan says:

    should resistor be connect tn pin 3 and 8?

  31. soldeerridder says:

    common cathode (second circuit) does not work.
    In the first circuit a 0 turns a segment on, where in the second circuit a 1 causes the segment to lid.

  32. Abhishek thakur says:

    hey i wanna make a pass key controlled interactive parking system….please help me by suggesting thge code…..

    only authorised people can park the car,means they have a password to open the gate and on the gate itself the LCD is showing the number of places epmty for parking.

  33. Abhishek thakur says:

    reply soon

  34. jey says:

    can i ask if how i can display 1 and 2 using push buttons,seven segment common anode,74ls47 and 74ls190.thank you.hope i can have a reply as much as possible

  35. jey says:

    mga puta kau bket hindi nyo nlagay ung leter ng 7 segment

  36. jyoti says:

    hello…am a 2nd year student so can u answer me 1 question and my question is:-

    So plz give me answer in detail………
    my email id is :-

  37. aldwin says:

    we have a project in our subject, and it was based on the elevator. when you input 1, it requires to light up the LED #1, and display 1 in 7-segment. Using this materials, 7 segment, 8 LED, 7447, and a parallel port. can anyone help me? ps. using .asm file?

  38. parth arora says:

    hey do u knw how to interface 7 segment common cathode to pic 18f4520 using ic 7447
    if anyone knw plss mail me that
    my id is
    plss send that

  39. kumar deep says:

    i want to interface 7 segment with 89c51 using single loop and without any middle ic

  40. Priya says:

    shall i use 8051???????

  41. Amar Singh says:

    from where can I got the internal circuit diagram of BCD decoder? Plz help me.

  42. christopher Akugbe Umweni says:

    Please kindly give me the circuit diagram of the Digital substitution board with LCD display of two digit on one side or two sided for a football substitution.

  43. christopher Akugbe Umweni says:

    Please kindly give me the circuit diagram of the Digital substitution board with LCD display of two digit on one side or two sided for a football substitution OR direct me where to get the design and construction of this substitution board.

  44. nini kahn says:

    i m new here..can anyone tell me how to design a decoder to display binary numbers using 7-segment display

  45. vahid says:

    تفاوت تراشه 7447 و 7446؟

  46. Sandilya (sandy) says:

    hey i m 12th grade student and want to know how does one make a decoder which shows the digit’s from 1 to 5 one who knows can please mail me at my ID

  47. Franklyne says:

    That’s wonderful. Could please send a circuit for 2 x 7 segment LEDs or two digit display with 7447 and 74148? Thanks

  48. ash says:

    kindly check the circuits b4 putting them online!!! pls do not give wrong info in the excitement of posting something!! the second circuit is such a blunder…. it doesnt work at all!!

  49. VIVEKANAND says:

    i want’s to give input to 7447 from the basic gates. is it possible to get bcd equivalent on 7 segment display.
    2) required 7 segment display is common cathod or common anode

  50. RAJASEKAR says:

    is ic7447 works with common cathode circuit please help me…..!
    my email id is

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