Microcontroller and 7 segment display question.

[sommes]

I would like to ask Is 7 segment decoder/driver necessary to connect 7
segment display with Atmel 90S8535 microcontoller.

 

[John Fields]

I would like to ask Is 7 segment decoder/driver necessary to connect 7
segment display with Atmel 90S8535 microcontoller.

 

[sommes]

Thanks for quick reply...
What if i want to use a 4 digi 7 segment display to represent 10bits output
from ADC.
Do I need a mutliplexer?

Thank you very much.

 

[Rene Tschaggelar]

I would like to ask Is 7 segment decoder/driver necessary to connect 7
segment display with Atmel 90S8535 microcontoller.

You can multiplex the anodes and cathodes yourself.
That depends what other stuff the 8535 does at the
same time.

Rene

 

[[email protected]]

I would like to ask Is 7 segment decoder/driver necessary to connect 7
segment display with Atmel 90S8535 microcontoller.

If you have 7 + number of digits output bits with sufficient current
handling (usually not a problem) you can do the segment decoding via a
lookup table in software, and the digit multiplexing with a fairly slow
interrupt service routine.

With an external decoder (74hct138, etc) you can only need log2(number
of digits) plus the 7 segments. A decimal point will cost you an 8th.

 

[John Fields]

Thanks for quick reply...
What if i want to use a 4 digi 7 segment display to represent 10bits output
from ADC.
Do I need a mutliplexer?

---
No. My favorite trick is to use something like an Allegro A6276.

Basically a shift register with constant current outputs which can
drive the segments directly, and with only _one_ resistor needed to
set the segment currents.

At the µC you only need three IO's to drive the chip's serial data,
clock, and latch enable outputs.

Here's a link:

http://www.allegromicro.com/datafile/6276.pdf

If you don't mind using current-limiting resistors and you use
high-efficiency displays, you could use plain ol' vanilla CMOS
HC594's or HC595's to do the job.

 

[sommes]

Thank you Rene,

Would you mind to give me some more details.

 

[sommes]

Thank you John.

Thank you for your useful information.

 

[Spehro Pefhany]

Thanks for quick reply...
What if i want to use a 4 digi 7 segment display to represent 10bits output
from ADC.
Do I need a mutliplexer?

Thank you very much.

Eight port pins and one or two passives is about the minimum circuit
cost/complexity.


Best regards,
Spehro Pefhany

 

[Jonathan Kirwan]

For hobbyists doing one-offs, too bad Digikey doesn't offer the DIP
(EA) form in 1's and Mouser doesn't even carry Allegro. Still, I'm
glad to know about it, now.

Jon

 

[John Fields]

For hobbyists doing one-offs, too bad Digikey doesn't offer the DIP
(EA) form in 1's

---


Always leave 'em laughing!

Seriously, though, that part (the 6276) saved a project once, when a
client decided to go to LED from LCD and I had a

 

[Don Lancaster]

Thanks for quick reply...
What if i want to use a 4 digi 7 segment display to represent 10bits output
from ADC.
Do I need a mutliplexer?

Thank you very much.

A hardware or a software multiplexer dramatically reduces the number of
leads going to the LED display.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[John Fields]

A hardware or a software multiplexer dramatically reduces the number of
leads going to the LED display.

 

[petrus bitbyter]

I would like to ask Is 7 segment decoder/driver necessary to connect 7
segment display with Atmel 90S8535 microcontoller.

As so often it depends... And there are almost always more ways to skin a
cat. It takes twelve pins, twelve resistors, four transistors, enough time
and some software to make the micro do it on its own. If you can fullfill
these requirements, you don't need a decoder. You can even save a pin and a
resistor if you don't need the decimal point.

As an alternative you can try to find displays with build in
decoders/latches, like TIL311. Still requires eight pins or more if you need
the decimal points. Can be reduced to three pins if you feed them via shift
registers like the old LS164. (You will need two of them for the digits plus
one for the decimal points.)

You can even consider to use (four) shift registers to drive the seven
segment displays directly. But as the LS can only handle limited current
(8mA if memory serves) you may need either buffers or use high efficiency
LED displays.

petrus bitbyter