7segment spi

misel0019 · Joined: 04 Oct 2010 Posts: 53 Location: Dhaka

hi,
i am again.
im stucked with a problem.

Problem:
i need to drive a large no. of (like 35) 7-segment by one controller.

how can i do that so easily.
by using 4-16 decoder for 7seg select and a bcd for generating number.

or

i can use 74HC595 for serial communication is it possible to control a large number of 7-seg without flickering.

which is the best way spi or using decoder??????

Regards
Misel

temtronic · Posted: Thu Nov 25, 2010 7:22 am

Using 3 pieces of 4:16 decoders would require 7 I/O pins plus 7 for the segments.
This matrix would be the fastest to update, minimal flicker. Did this eons ago using 8031 in asm, that was 'fun' but rewarding.

Using the 74HC595 serial might be easier to program,depending on skill level, but will have flicker, if the chain is long (35 displays). You could break up the chain into smaller sections (say 7 displays each), so you would need 5 sections(5 *7=35). I don't think flicker would be a problem.

POWER is though ! Be sure the power supply driving the LEDs is at least 2x the computed spec and well filtered, with good decoupling from the PIC power supply.

hisham.i · Joined: 22 Aug 2010 Posts: 43

Hello,

You can use max7219 to drive up tp 7 dig 7 seg display for each i max7219, and if you put 5 max7219 in cascade you can drive the 35 digits 7 seg display you want.
Max 7219 uses SPI for data comunication, and I advise you to download the datasheet of max7219 and read it carefully to know how to use it.
gd luck

pmuldoon · Joined: 26 Sep 2003 Posts: 218 Location: Northern Indiana

Another chip to look at is the MC14489.
It will drive 5 displays per chip via the spi bus, and can be daisychained.
http://www.freescale.com/files/timing_interconnect_access/doc/inactive/MC14489B.pdf

misel0019 · Joined: 04 Oct 2010 Posts: 53 Location: Dhaka

Thanks temtronic, hisham.i and pmuldoon for giving nice help to get rid of the problem. I'm trying with all.

Regards
Misel

alaa.a · Joined: 05 Dec 2010 Posts: 1 Location: Damascus, Syria

I'm on a project, I have fourteen 7 segment...
after reading previous posts I decided to use :

BCD to 7 segment "4511" for data, that takes 4 pins.
4:16 Decoder "74152" for controlling the segments (Common Cathode) and that takes 4 pins too.

Is it OK? or you have different suggestions?

another question :
If is it OK with that ICs, Is there any need to add "ULN2003" after "4511" to drive the load?

Regards
Alaa