Devuhm:
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] ?
Devuhm:
The display will be blinking?
The anodes will have to be strobed
Devuhm:
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.
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.
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.
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!
Devuhm:
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.
Devuhm:
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.
