How many Arduino pins can you dedicate to driving the display?
Driving (9x 4digit) 7-segment displays. (12x3 digits)
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5th December 2011 03:23 AM #1Panici
Driving (9x 4digit) 7-segment displays. (12x3 digits)
Bear with me, this my first project.
Please include details that are assumed knowledge to an experienced person.
I'm planning to build an external display for PC racing simulators (ie. rFactor)
Mock up:
The plan is to build on breadboard then transfer to perfboard at a later date.
I'm going to use 9x red 4-digit modules (0.56") from here [12 pin version]:
http://www.kingbrightusa.com/categor...+0.56in&Page=1
Should I get Common Cathode, or Common Anode?
My main concerns right now are:
1. Power - How to physically wire power to all of the displays. (using a 5v bench supply most likely)
2. Data Transfer - How to get the data from the arduino onto the displays. (multiplexing? hardware/pin wiring?)
3. Fast display refresh rate/speed - I've seen displays lag with only four 7-segment displays, so i'd rather use extra pins on the Arduino then daisy chain.
4. Special characters. - In addition to (0-9,A,B,C,E,F) Ideally I want to be able to use the segments to form whatever other letters I can. (n, r, o, d, b, etc)
Oh and also, while talking about speed, I plan on also driving two (possibly 3) of these using the (TM1638) library.
http://www.dealextreme.com/p/8x-digi...d-module-81873
Let's leave the TM1638 based modules out of the equation for now, unless we need to somehow wire them together with these displays, in order to not have display lag???
I obviously cannot drive (9x12) pins right off of the arduino, so what is my best option?
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5th December 2011 01:08 PM #2alec_t
0My circuit designs should be regarded as experimental. Although they work in simulation, their component values may need altering or additional components may occasionally be necessary when the circuit is built. Due safety precautions should be taken with any circuit involving mains voltage or electrostatic-sensitive components.
Alec's First Law:-
Every problem has a solution (given the right information and resources).
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5th December 2011 04:29 PM Thread Starter #3Panici
I'm using an Arduino Mega, which has 54 digital IO pins.
I'd say using 40-45 for the display is reasonable.0
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20th June 2012 08:04 PM #4windozeuser
Shift registers would be useful here
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30th June 2012 03:38 PM #5elfcurry
Let me recommend a MAX7219 chip if you go for common cathode displays. Each chip can drive eight digits and handles the multiplexing timing autonomously, so you'd need six of them (two per display row) to keep it tidy. I'd been wondering what using them to control a whole bank of 7-seg displays would be like (eg an Apollo flight computer display) and this is it!
I bought some on ebay and they're cheap and easy to use. You clock the data into them serially and each digit is one internal RAM byte. You can use the internal seven segment decoders or choose to override any digit with a segment pattern of your own. It contains current drivers and uses one resistor per chip to set the segment current but you also have digital brightness control. You can also use them for dot displays up to 8x8 and I have done so with success.0Last edited by elfcurry; 30th June 2012 at 03:44 PM.
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30th June 2012 03:54 PM #6ronsimpson
There are many 7-segment LED drivers, Here are 3 of them.
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30th June 2012 06:52 PM #7elfcurry
Yep, I'm sure there's a lot of choice. Out of those three I'd still go with my low-parts-count (six chip), low-cost MAX7219 suggestion over those other much older single digit driver (ie high-parts-count: 36 chip) alternatives providing he's happy to use common cathode displays and go for a multiplexed design.
0Last edited by elfcurry; 30th June 2012 at 06:57 PM.
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30th June 2012 08:38 PM #8ronsimpson
How big a display do you want?
http://www.sparkfun.com/products/8799
Here is a 4"x5" LCD display (graphic) that can do the job. You will not have to constantly scan the LEDs.0
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30th June 2012 10:29 PM #9elfcurry
Yes that's a nice alternative - if he hasn't got his mind set on 7-seg display.
.... same with the MAX7219 which does it for you as I said, unlike those 4511 and 7447 single digit drivers."You will not have to constantly scan the LEDs"
Anyway, the OP asked the question six months ago so he probably decided by now.0Last edited by elfcurry; 30th June 2012 at 10:32 PM.
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30th June 2012 11:37 PM #10ronsimpson
Or he has not started yet. (like me)
Originally Posted by elfcurry
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