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Topic: 4 x 7 segment display question (Read 2890 times) previous topic - next topic


Feb 04, 2013, 01:07 am Last Edit: Feb 04, 2013, 01:13 am by jtw11 Reason: 1
Evening all,

I want to drive four 7-segment displays to display a number with the format xx.xx, so instead of using four separate 7-segment displays, I thought it must be possible to purchase a unit with four digits in one.

I've just found these on SparkFun - four displays in one, however - the pinout bemuses me, there are 12 pins - 4 of which are common anodes, okay. However, the other 8.... well, it seems to me you can only control all four digits at the same time, i.e. only display the same number four times, on each digit? As the same segment section has a common cathode connection to one of the pins?


A single digit display has typically 10 pins yes, 7 for the segments, one for the decimal place, and two for a common anode/cathode - so I was expecting 32 pins just for the segments, not including commons?

So, am I missing the point well and truly - or with that SparkFun display, can I only have the same digit four times over? One of the images seems to show otherwise?

EDIT - It seems all combined displays are like this - http://www.farnell.com/datasheets/677505.pdf

Surely these arn't only for displaying the same digit x 4?

Although, here's a 36 pin version - http://www.farnell.com/datasheets/1519763.pdf but the question still stands about the other ones?


You can display any combination of segments and one anode at a time, If you display them in order fast enough they will appear to be continuously  due to the eyes "Persistance Of Vision". Google POV.

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Ahah! I was thinking the latter, but thought I was potentially going somewhat insane...

I'll use a full pinned version in a first attempt, then move on to the low pin count displays - I'd imagine the code for these is somewhat more complex.

On another note, I'm thinking how to drive so many pins - it seems there would be lots of different ways; port expanders, multiplexed latching etc...

EDIT - Saying that, that's just a lazy excuse because it's late at night... I could save loads on hardware and just do it in software using the low pin count displays.


Yes, lots ways. Here's a few.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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