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Author Topic: 4 digits 7 segments with shift regitry ?  (Read 897 times)
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Hi Guys,
i know the forum is full of this kind of topic, but i couldn't find an answer.

I would like to drive a 4digits 7sergments and i found a 12pin display
Here there is what i wanna do:

http://ecotronics.ch.honorius.sui-inter.net/wordpress/2013/multiplexed-4-digit-7-segment-led-display-mit-arduino-ansteuern/

My question is can I add as 74HC595 shift registry to drive the 8 pins so i can use in total only 7 pins instead of 12 ?
The display will be blinking?

Many other display have a common anode: https://www.sparkfun.com/products/9483
Is it possible to use 74HC595 also for common anode ? Or how to do it ?

Thank you
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My question is can I add as 74HC595 shift registry to drive the 8 pins so i can use in total only 7 pins instead of 12 ?
Meaning: 4 for anode select and 3 for shift register control [data, clock, /OE] ?

The display will be blinking?
The anodes will have to be strobed

Many other display have a common anode:
Is it possible to use 74HC595 also for common anode ?
By sending LOWs/0s (as data) for ONs

Attached is the circuitry for a 2-digit display.
It's a lot less trouble to use 4 discrete 7-segment displays with a separate shift register for each ("daisy-chained") - you don't have to repeatedly tend to the strobing chore, you just shift out your data and go on with life.



* Seg7x2no5.jpg (39.99 KB, 596x393 - viewed 35 times.)
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So you suggest to user 4 shift registry one each 7segment display. In total i will be using 3+7 right ?
The display if i well understand has to be common catode ?

And if I have common anode which pin I have to send to ON the led ? This is not clear to me.

Thank you a lot!

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The display if i well understand has to be common catode ?
No you do not well understand.

It can be either a common anode or common cathode depending on if to choose to wire the segments up for current sourcing or current sinking.
If you have one shift register for each display then there is no need to multiplex them or strobe the common common component.
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Since i still have to buy components, in your opinion the best solution is.. ?
tnx!
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Best is hard to define with no context.

With a shift register for each display the segments are on all the time and it only consumes CPU time when you are changing what the display shows.

With one shift register an strobeing  anode / cathode requires constant refreshing from the arduino - but the hardware is cheaper and easier to wire up.
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Hi, I made some tests and things seems a bit more clear to me.
I'm planning to use 4x7 segmnet display, 4x74HC595 driven by 4 transistors + resistors. I should be able to use only 3+4=7 pins.
But now i have one doubt: at the same time it might happen that 32 leds are on, since i'm not multiplexing. Isn't it too much for arduino ? It's necessary to use external power supply ? (considering also that my final project needs 20x7 segmnent display)
Thank you a lot!
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Since i still have to buy components, in your opinion the best solution is.. ?


If you haven't already bought the components, I suggest you get a single common cathode 4x7 display and a 7221 driver. It really can't get any simpler, and all you need to know is here.

http://playground.arduino.cc//Main/MAX72XXHardware

here is some further info which may help

http://forum.arduino.cc//index.php?topic=172192.msg1279382#msg1279382
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Hi, I made some tests and things seems a bit more clear to me.
I'm planning to use 4x7 segmnet display, 4x74HC595 driven by 4 transistors + resistors. I should be able to use only 3+4=7 pins.
But now i have one doubt: at the same time it might happen that 32 leds are on, since i'm not multiplexing. Isn't it too much for arduino ? It's necessary to use external power supply ? (considering also that my final project needs 20x7 segmnent display)
Thank you a lot!

You don't need any transistors with 4 separate 7segs.
20 mA each is unnecessary, especially since there's no strobing, 10 mA each ought to be plenty.
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Hey, why not just buy one of these and figure out what to do with the extra digits?

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