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LED Sign Board 30X7 - PIC16F628A

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Gayan Soyza

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Here is another simple project that I have made for a taxi service.

Message "PILIYANDALA CABS + arrow" moving all 4 ways.

Here is a small video
YouTube - LED Sign Board 30X7

18 pin micro PIC 16F628A driving 210 LEDs (30X7) by the use of external drivers.

Code I cannot publish the code bcuz I'm cheating the client.Its simple to accomplish Sorry about that.

Pictures are very bad sorry about that.
 

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Actually there is no any row drivers (can you believe it?) Only the column drivers using ULN2803A.ULNs driving through Jonson counters.I did not use shift registers because I have plenty Jonson counters at home.

The secret is in the software & in that special LED.
 
Actually there is no any row drivers (can you believe it?) Only the column drivers using ULN2803A.ULNs driving through Jonson counters.I did not use shift registers because I have plenty Jonson counters at home.

The secret is in the software & in that special LED.
So 7 columns per ULN2803 with a matching 74HC4017 driving rows?

Four pair of ULN2803 and 74HC4017? Isn't that only 28 columns?

<added>

Oops! Sorry! ULN2003 is 7 bit driver and ULN2803 is 8 bit driver...

BTW, I forgot to say --> very nice implementation.....
 
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Hi Mike I have 30 columns.From ULN 8 X 4 = 32 the last two outputs from the last ULN I kept free so 30.

From 4017 I took 8 outputs each. 8 X 4 = 32 the last four outputs from the last 4017 I kept free so 30.:)
 
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I'm confused. I assumed you were driving rows with the 74HC4017's but now I realize there's no practical way to provide 30 bits of data onto the four ULN2803 inputs. How are you scanning this matrix? Schematic?

Mike
 
I'm confused. I assumed you were driving rows with the 74HC4017's but now I realize there's no practical way to provide 30 bits of data onto the four ULN2803 inputs. How are you scanning this matrix? Schematic?

Mike

:D

The row side driving from the uC through a resistor & the columns shifting from Jonson counters.

To provide CLOCK to Jonson counter I have taken 4 pins from PIC.

I could use 8 bit serial registers for this case but I had plenty Jonson counters at home.
 
Gayan,

So, are you driving 4 columns and 1 row during each display interval (1/28th or 3.57% duty cycle)?
 
1/30th :)

Display interval I mean the column interval it is used to give a clock to J Counter to shift into next column + to show the display.

How did you get that 3.57% duty cycle sir?
 
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1/30th :)

Display interval I mean the column interval it is used to give a clock to J Counter to shift into next column + to show the display.

How did you get that 3.57% duty cycle sir?

1/28 = .0357

How do you get 1/30th duty cycle? Are you selecting one row and one column each update interval to light a single LED?

Can you provide a schematic? I recall you have not done so in the past when asked.

Mike
 
Because I have 30 columns not 28.I wonder how you get 28?

1/30 = 0.033

I could provide a sample schematic but it will take some time because now I'm at some other place :)

Forget the row side simply shift the columns while inserting data to PORTB.
 
Ok, ok. I understand. I'm very "dense" today (grin).

Thank you for the explanation and for being so patient.

Again, very nice design! It uses many ICs but they are very inexpensive ICs so that is a good trade off. And you seem to be getting very good brightness for only 1/30th duty cycle.

Take care my friend.

Mike
 
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Wait Master! I cannot leave you.

I have a question take your own time & answer me.

If you get a signboard that it needs 100 columns & 7 rows.What method do you prefer to do the code? How do you scan your display?

No need code & no need schematic just give your idea.
 
I would prefer to "scan" the rows to increase duty cycle and reduce "peak" current requirements for full brightness.

You could easily modify and expand your 7x30 circuit using this method;

(1) remove the current limiting resistors from the row pins.
(2) install row driver transistors. you'll only be driving one row at a time.
(3) use 74HC164 or 74HC595 or similar 8 bit shift registers for the columns.
(4) drive the ULN2803 sinking drivers from the shift register outputs.
(5) install current limiting resistors on the ULN2803 outputs.

Actually, you'll probably want to use row driver transistors for every 10 or so columns unless you install some very "big" transistors (grin).

I would actually use 8 bit serial-to-parallel sinking driver ICs for the columns instead of the dual IC combo' but they're expensive. For the dual IC combo' I guess I would choose the 74HC595 over the 74HC164 because the '595 has a latch which would allow us to take our time loading 100 bits of data into the shift registers without messing up the display. The '595 also has an output enable pin which could be driven by a PWM signal to control display brightness.

Regards, Mike
 
With the very good brightness you're getting on your 7x30 display with only a 1/30th duty cycle, I am thinking that you might actually have several different options for an expanded 7x100 version. Perhaps you don't really need to use 13 74HC595's and 13 ULN2803's for a 1/7th duty cycle 7x100 display.

Let me think about this and get back to you Sir.

Mike
 
Master are you there!

Ah yes that 74HC164 is one of my favorites & I have done some few boards using that.I have attached one of my PCB layout done in past.

I'd like to do a row scan to a large column displays.

Thanks for your information.

A bit off topic what you doing these days sir?
 

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Hi Gayan,
That's a nice display. What Led's did you use? I am trying to build a sign just like it.

It’s a type of super bright LED designed for signboards.

Forward current 20mA (operating below that with the same brightness)
Forward voltage 1.9V
Viewing angle below 30 d.

Actually there were no many that type of LEDs in my place so I have to shift to a ready made MATRIX.
 
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