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Topic: Best way to use 30 7-Segment Displays (Read 497 times) previous topic - next topic

Mazon

Jan 09, 2016, 10:26 pm Last Edit: Jan 09, 2016, 10:36 pm by Mazon
Hey everyone,
I'd like to control 30 7-Segment Displays with an Arduino board. You should know in advance that this is my first project of this kind. I newer drew an electric circuit before, never soldered anythink. Only thing I'm quite good at is programming :)

So a friend of mine had this idea to build a panel to control a flight simulator. (I know, this isn't new and you can buy stuff like this for little money, but we want to to it anyways to gain experience)

So we need to display 4 frequencies (6 digits each) and another 6 digits to display autopilot data. That makes 30 digits.

What we did so far:
Both of us know close to nothing about electric circuits, so we read alot tutorials and watched a few videos to make ourselfs more familar with this "kind of stuff".

We obviously want to use as less output pins as needed on our arduino. So far we like to use the Arduino Uno (not sure if that's possible though). In this configuration we'd need 12 pins to control the displays, which would only give us 2 for other inputs. So if we can't come up with a different solution we might go for the Arduino Due.

Some questions:
First of all, attached is a layout for an electric circuit, you may want to have a look at it since the questions basically base on it. (The displays we got are common cathode)

1) Will we get a "good" result when multiplexing 30 displays? Or will this lead to flickering and/or low brightness?

2) I looked for a shift register with more than 8 bits, which would make everything a bit less complicated, but I couldn't find anything specific.

3) I didn't put in any resistors yet, just because I'm not sure whether I need them or not, since we have 5V input, and our components all seem to handle 5V just fine.

Any other thoughts on this? For me it seems like there must be a simpler and more elegant solution to this.

Best wishes,
Mazon

Edit: Our displays are 10 3-Digit 7-Segment modules.

Paul__B



Wow!  Ugly!

You need to use MAX7219s.  Readily available on eBay and these seem to be generally reliable.

Don't even dream of using the horrible mash-up you describe above!

Mazon

#2
Jan 09, 2016, 11:34 pm Last Edit: Jan 09, 2016, 11:39 pm by Mazon
Well that's a way of motivating someone who's trying to get a grasp of something.

Thanks for the MAX7219 anyway.

I have to admit that I'm not aware of the possibilities some chips may offer, so I tried finding a way with the things I knew about.
Guess I'm asking straight away next time, without thinking about a solution myself...

Paul__B

#3
Jan 10, 2016, 08:29 am Last Edit: Jan 10, 2016, 09:00 am by Paul__B Reason: Bulk price amended
Well, you come here for experience, which might well include the complete solution!

When you consider that four MAX7219s plus only four resistors and eight capacitors will do the job for you, and you do not need to concern yourself with multiplexing and it only requires three port pins to control it, it's pretty much a slam-dunk.

Or maybe you just go buy five of these and ignore the extra two digits on each (you set the Scan Limit register in the MAX7219 to 7 and you only have a 6-way multiplex so you get superb brightness).

.

Mazon

#4
Jan 10, 2016, 08:57 am Last Edit: Jan 10, 2016, 02:06 pm by Mazon
Yes of course gaining experience might include getting the solution on a silver platter. But it doesn't have to include the words "ugly" and "horrible" to describe the work of someone who did the best they could with their knowledge at that point.
But anyways, the MAX7219 indeed solves all my problems, and therefor your answer was very useful.

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