Gayan Soyza

I built a 10x7 led signboard using PIC16f84a.just to get some experience in making moving signs.It consist of count down,scaning from left & right,hold on display,elevator method,adding letters......etc.

Unfortunately I coudn't find any led matrix so I used normal 5mm led's.no mo memory space in the pic to add more patterns only 2 lines left in program memory.

see the attachment for a small video.

Attached Images

10x7 Signboard.JPG (285.4 KB, 526 views)

Attached Files

10x7 Display.zip (554.4 KB, 519 views)

Nigel Goodwin

So why use a prehistoric PIC?, simply changing it for it's 'modern' replacement the 16F628 doubles your program memory.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

Mike, K8LH

Bravo Gayan! A very impressive demo' and effort.

Happy Holidays. Michael

tdg8934

I have built a similar one using a Parallax Basic Stamp II and also ported it over to a Parallax SX-28 microcontroller. Both are written in their version of BASIC and use 4017 chips and transistor/chip buffers to drive the LEDs across. I have built a custom 20 x 7 and want to build a larger one sometime. It only scrolls (lettters, symbols or whatever) from right to left. Do you have a schematic of yours. I am not a PIC programmer but would like to see how you did it. I spent a lot of time learning this as there wasn't too much available on the web about this. Any schematics and code would be nice too.

Thanks,

Tim

Nigel Goodwin

Check my PIC tutorials, the latest one implements an 8x8 matrix of LED's, with full alphanumeric fonts and four way scrolling - there's also a couple of videos of it working.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

House0Fwax

Judging by a diagram Gayan Soyza posted a while back, I think it's based on this design : http://users.tpg.com.au/users/talkin...ion-Part1.html

Mike, K8LH

Hi Tim,

I'd be happy to share a slightly more advanced design if you're interested.

This design with 9 pin interface will drive one to seven 8x8 matrices to full brightness. It uses the PWM signal from the PIC for brightness control and to multiplex the 8 pin PORTB "row driver" bus with the '5821 column driver "CLK" and "DAT" lines to allow loading the shift registers on up to seven '5821 column driver ICs in parallel in about 24 cycles (4.8 usecs).

I can provide simple interrupt driver examples in another post, if you're interested.

Happy Holidays. Mike

Attached Images

	Matrix Display (9 pin design).PNG (34.1 KB, 672 views)
	Matrix Display (10 pin design).PNG (34.0 KB, 96 views)

Mike, K8LH

Hi again Tim,

Just thought I'd mention that I've used an 8-pin interface version of this design in the past using a 16F88 with the RB0 pin configured as the CCP1 PWM output. I've included a drawing that shows how one might wire up 5x7 type LED modules.

There's also a TI serial-to-parallel sinking driver IC with 150-ma outputs which I suspect may work well in these designs. It's the TPIC6B595. I have samples but have not tried them yet.

Regards, Mike

Attached Images

Matrix Display (8 pin design).PNG (33.6 KB, 601 views)

tdg8934

Mike,

A very impressive design!

Here are my designs for a 20x7 display (attached zip).

I have also tried using the MAX7219 chip to drive more than 64 LEDs but can't figure out how to cascade 2 or more of them.

Currently I am working on a SX-28 (7 rows) and 8255 PIA (up to 24 columns) version and have working code to send data out to the 24 LEDs but need to work on the scanning. I am trying to not use a 4017 and only an SX-28 microcontroller and a 8255 chip but I cant figure out how to send data to RB and RC at the same time unless an interupt is used. Otherwise 1 row has data for every collumn and it needs some scanning on the 7 rows I think for persistance of vision.

Attached Files

MovingLEDv1_1.zip (168.2 KB, 262 views)

ali_raza117

can u make this circuit for moving text usnig MAX6952 or MAX6953,
i need them,i want to make thse moving text display in Proteus,
can u help me,

Mike, K8LH

Hi Tim,

Nice design and nice schematics. A few comments;

<1> Too many chips (grin).

<2> It seems you're scanning columns for a 1/20th or 5% duty cycle but the ULN2003 sinking column drivers you've chosen limit peak current in any column to about 500-ma. Unfortunately with a 5% duty cycle you'd need to sink a peak current of approximately 200-ma/LED or 1.4-amp/column for full brightness. You really should consider a design that scans rows at a 1/7th or 14% duty cycle or scans columns at a 1/8th or 12.5% duty cycle.

<3> I'm surprised you're not using an interrupt driver which reduces display management to a simple "low overhead" background task allowing your main program to simply stuff the display buffer.

~~~~~~~~~~~~~~~

There are many different ways to drive large LED matrices. Here's another example that's a bit more modular.

Instead of driving and scanning one large row I scan columns at a 1/8th or 12.5% duty cycle. Each 8x8 module has it's own row driver/latch and column driver transistors. All of the column 1's in each module are driven at the same time, then all of the column 2's, etc. Current requirements for full brightness at a 12.5% duty cycle are approximately 80-ma/LED or 640-ma/column per module. Instead of using eight large 10-amp column driver PFETs for the entire matrix of modules I decided to use eight small 2.4-amp column driver PFETs for each individual module to reduce size and heat dissapation. Anyway, I'm sure you get the idea.

Regards, Mike

Attached Images

Concept - Clock 8X8.JPG (141.8 KB, 667 views)

Nigel Goodwin

EPE recently did a similar project, with a PIC 16F628 on each board, and the displays stacking together just like that. It can have 128 boards stacked together, all fed from one master board with a 16F628 and a MAX232 for a PC connection.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

ali_raza117

hi look at my circuit and code but its not working,its built in Proteus,and Protgramming in Mikroc
can u correct the problem,?

Attached Files

MAX6952.zip (52.5 KB, 126 views)

Mike, K8LH

Sorry, I don't have either so can't even look at your schematic or code. Perhaps another Forum member can take a look.

Regards, Mike

Mike, K8LH

Unfortunately, referencing an EPE article has little value if you're not a subscriber. Too bad.