how to latch 7 segment display??

[soohino]

I have a question here. If i wanted to make my output data in 3 digits with 2 decimal points (Example: 2.98V , 3.27V ...... the range is from 0.00V - 5.00 V). So after processed by the microcontroller, how can i connect them(i have 3 7 segment displays)?how can i latch those 7 segment displays in a single port? is it a latch IC is needed for one 7 segment display?? by using latch, what have to be considered when writing assembly code?

p/s: anyone know what kind of latch IC is easily get in market??

Urgent! expert plz help~~ thanks~~~~~~~

 

[Nigel Goodwin]

You don't need a latch, you can do it totally in software by multiplexing the display digits. You need one output pin per segment (so seven in total, or eight with the decimal point), plus one per display - so three more for your three displays.

 

[JimB]

As Nigel said, you dont NEED a latch, however have a look at Nationa Semiconductors MM5450.
It has 35 output latches and is serial loaded, minimising the number of output pins you need to use on your micro/PIC.

JimB

 

[checkmate]

Nigel's method is called LED multiplexing, no additional hardware required. Essentially, you output to the 3 LEDs sequentially, so each LED will be on 33% of the time. But because the output is done at a high enough frequency, the human eye would not see any visible flashing.

 

[soohino]

thanks nigel!!

im not understand your last sentence. can you further explain here??
according to u, there is no need to use a latch chip, just involve the software part only. then meaning 3 digits would be shown at the same time or not?

do you have any sample source code for this for my reference?


to checkmate:
thanks for your help as well.

and can u explain this more :

But because the output is done at a high enough frequency, the human eye would not see any visible flashing.

do you mean we cant see the output properly? then got any solution or not?

 

[Nigel Goodwin]

thanks nigel!!

im not understand your last sentence. can you further explain here??
according to u, there is no need to use a latch chip, just involve the software part only. then meaning 3 digits would be shown at the same time or not?

do you have any sample source code for this for my reference?

You don't mention what processor you're using, but for a PIC example consult my tutorials - where I multiplex two seven segment LED displays.

Multiplexing shows each digit in turn, but it's speed makes them appear together - see below for why!.

to checkmate:
thanks for your help as well.

and can u explain this more :

But because the output is done at a high enough frequency, the human eye would not see any visible flashing.

do you mean we cant see the output properly? then got any solution or not?

It's an effect called 'persistance of vision', if you sequence the digits fast enough you can't see them flashing - a television works in a similar way, showing 25 (or 30) still pictures per second, your eyes don't notice the pictures changing, but give the impression of a moving picture.

Because you are only displaying each digit for 1/3 of the time, you need three times the drive current to give the same brightness.

Almost everything you see with multidigit displays (either LED or LCD) is very likely to be multiplexed, it gives so many advantages to a design.