►Seven-Segment Display Example

The segments in a 7-segment display are arranged to form a single digit from 0 to F. We can display a multi-digit number by connecting additional displays. Even though LCD displays are more comfortable to work with, 7-segment displays are still standard in the industry. This is due to their temperature robustness, visibility and wide viewing angle. Segments are marked with non-capital letters: a, b, c, d, e, f, g and dp, where dp is the decimal point. The 8 LEDs inside each display can be arranged with a common cathode or common anode. With a common cathode display, the common cathode must be connected to the 0V rail and the LEDs are turned on with a logic one. Common anode displays must have the common anode connected to the +5V rail. The segments are turned on with a logic zero. The size of a display is measured in millimeters, the height of the digit itself (not the housing, but the digit!). Displays are available with a digit height of 7,10, 13.5, 20, or 25 millimeters. They come in different colors, including: red, orange, and green.


The simplest way to drive a display is via a display driver. These are available for up to 4 displays. Alternatively displays can be driven by a microcontroller and if more than one display is required, the method of driving them is called "multiplexing."


The main difference between the two methods is the number of "drive lines." A special driver may need only a single "clock" line and the driver chip will access all the segments and increment the display. If a single display is to be driven from a microcontroller, 7 lines will be needed plus one for the decimal point. For each additional display, only one extra line is needed. To produce a 4, 5 or 6 digit display, all the 7-segment displays are connected in parallel. The common line (the common-cathode line) is taken out separately and this line is taken low for a short period of time to turn on the display. Each display is turned on at a rate above 100 times per second, and it will appear that all the displays are turned on at the same time. As each display is turned on, the appropriate information must be delivered to it so that it will give the correct reading. Up to 6 displays can be accessed like this without the brightness of each display being affected. Each display is turned on very hard for one-sixth the time and the POV (persistence of vision) of our eye thinks the display is turned on the whole time. Therefore, the program has to ensure the proper timing, else the unpleasant blinking of display will occur.



Connecting a microcontroller to 7- segment displays in multiplex mode


Program "7seg.asm" displays decimal value of a number stored in variable D.
Example:
movlw .21 	 
movlw D 	; number 21 will be printed on 7seg display


Displaying digits is carried out in multiplex mode which means that the microcontroller alternately prints ones digit and tens digit. TMR0 interrupt serves for generating a time period, so that the program enters the interrupt routine every 5ms and performs multiplexing. In the interrupt routine, first step is deciding which segment should be turned on. In case that the tens digit was previously on, it should be turned off, set the mask for printing the ones digit on 7seg display which lasts 5ms, i.e. until the next interrupt.


For extracting the ones digit and the tens digit, macro digbyte is used. It stores the hundreds digit, the tens digit, and the ones digit into variables Dig1, Dig2, and Dig3. In our case, upon macro execution, Dig1 will equal 0, Dig2 will equal 2, and Dig3 will equal 1.


The following example shows the use of the macro in a program. Program prints a specified 2-digit number on a 7seg display in multiplex mode.




◄ Previous Page  |  Next Page ►

Back To Index

Conversation

hareeshchamiyar
Thu Mar 29 2018, 10:47 AM
please help me for the configuration bits for dspic30f2010
hareeshchamiyar
Thu Mar 29 2018, 10:45 AM
can any one using dspic30f2010.
Thu Mar 29 2018, 06:03 AM
Neena
can anybody give solar tracking in 8051 using proteus and keil to mail [email protected]
ExperimenterUK
Mon Mar 19 2018, 07:33 PM
sorry bedo.. maybe next time
Sun Mar 18 2018, 07:48 AM
Mourya Manojkumar
Please send me circuit diagram and PCB diagram
Thu Mar 01 2018, 05:49 AM
Felixc
May you please help me with a code for programmable load shedding controlling 4 loads
Sun Feb 25 2018, 08:29 PM
ezeoke.charles
i need of it
Sat Feb 24 2018, 03:35 AM
Aaquib
I want help for digital ic tester
ExperimenterUK
Tue Feb 20 2018, 04:01 PM
Join up.. and post your problem
Mon Feb 19 2018, 11:17 AM
ashishkumar
i needs help for my project

Downloads

Comments

Pater
Fri Apr 20 2018, 02:38 PM
jamiel
Sat Apr 14 2018, 12:47 AM
akrepkral76
Wed Apr 04 2018, 07:51 PM
samanthaeaves
Mon Apr 02 2018, 06:27 AM
rana2056
Sat Mar 31 2018, 02:11 PM
Darshanparabbnb
Mon Mar 26 2018, 07:17 AM
marttinsmarcio
Sat Mar 24 2018, 12:31 PM
LAMBO
Tue Mar 20 2018, 09:51 AM

Online

Guests: 28, Members: 0 ...

most ever online: 182184
(Members: , Guests: 182184) on 06 Aug 2010: 05:37 AM

Members: 37994
Newest member: Pater
Forum Activity
Pater Avatar
Posted By Pater
Fri Apr 20 2018, 02:40 PM
Actually I want to transmit 3 bits serially using ...
ExperimenterUK Avatar
Posted By ExperimenterUK
Mon Apr 16 2018, 08:49 PM
On the diagram, a diode feeds a rectified sine wav...
LAMBO Avatar
Posted By LAMBO
Mon Apr 16 2018, 06:39 AM
Hi sir i haven't connected any serial connec...
ExperimenterUK Avatar
Posted By ExperimenterUK
Fri Apr 13 2018, 02:09 AM
I assume you are doing this project.http://www.805...
LAMBO Avatar
Posted By LAMBO
Thu Apr 12 2018, 06:51 PM
hii sir,I am working on ac motor controller .I hav...
ExperimenterUK Avatar
Posted By ExperimenterUK
Tue Apr 10 2018, 06:12 PM
The lpc214x has a 32-bit prescaler , so I would ...
Praneeth1299 Avatar
Posted By Praneeth1299
Tue Apr 10 2018, 09:16 AM
Hi,I'm generating constant frequency of 1hz and va...
akrepkral76 Avatar
Posted By akrepkral76
Sat Apr 07 2018, 01:57 PM
I have used diptrace.I think ı have recevied from ...
ExperimenterUK Avatar
Posted By ExperimenterUK
Sat Apr 07 2018, 01:45 AM
You will need to say which software you are using,...
akrepkral76 Avatar
Posted By akrepkral76
Fri Apr 06 2018, 12:22 PM
I have drawed many PCB board. But it is still not ...