24x12 matrix bicolor LEDs

[Jerry I]

Hi Again

Your display is getting more interesting.

We at the company I worked for made similar displays. Instead we used TPIC6B595 to drive the column with a series resistor like your first schematic and we used a FET to drive the rows like your second schematic. But instead of using a shift register on the gates of the FET try a 74HC138, decode the input to select 1 of 8 outputs. We would refresh the display row by row at frame rate 60HZ multiplexing. 8 x 60 = 500Hz. So load data first row turn on FET, Load data for 2nd row, turn off FET row 1, turn FET row 2, and so on till all 8 done.
Then do it all over again. The shift register in the input of the FETS would work too but I think the 74HC138 would be faster.
Since you are refreshing at such a high rate the LED current could be increased, because on time would be very short.

[tEaM]

The PIC16F648a only has 16 IO. I need 16 IOs + two RS485 ports. But this is no problem. I choose a pic with more pin. Ex. PIC16F876A

The leds that I will use are 3mm bicolor LEDs (red / green) with a forward current 20mA per color.

Theoretically, 1 PIC will control 8x8 matrix bicolor LEDs. 4x8 matrix of red color and 4x8 matrix of green color.

I use 74HC595 or use 16 IOs direct to the PIC, the only difference is save 2 IC's (74HC595).
For drivers, I prefer to use a ULN2803 and not the MOSFETS.

[temtronic]

oops..this is day 4 of my classic 'migraine type ' headaches so of course a 648 won't work...doh. I looked at my test unit it has an 18F46K22 on board. So you would need a 28 pin PIC for the job. Best to search for a low cost one WITH hardware UART.Since it only has to do RS485 and control a single display it won't need a lot of memory! You should use a xtal and caps for solid ,reliable communications though.

course now that you started this thread, I've ordered a 28 pin version of the 46k22 and some 8by8s.....sigh...maybe that will break my headache

Jay

[Jerry I]

Hi tEam.

If your using 8x8 matrix bicolor LEDs. it is not 4x8 matrix of red color and 4x8 matrix of green color.

Its 8x8 red and 8x8 green.

You will also need to sets of shift registers, one for red and green. different data per colour. Also if red and green LEDs are on it would produce yellow.

Jerry

[Mike Walne]

[temtronic]

I keep coming back here after thinking about the OP and recalled that 'Charlieplexing' was/is a way to easily get a PIC16F684 to control 64 LEDs in a matrix, have RS485 and a pin or two left over!
9 pins to control the LEDs, 3 for the RS485, 2 for xtal, leaving 2 pins for 'other stuff'. This would allow a very inexpensive PIC to be the 8x8 LED controller.
Communications could simply 2 bytes, address followed by data.
While the 648 is 1/2 the cost of an 876 it does require more 'programming' in order to design the algorithm and 'memory map' for controlling the LEDs, so it depends what's the driving factor coins in the pocket or level of expertise?
However since the OP has posted he might want to use RG LEDs , the more expensive PIC should be chosen..easier to program, easier to wire up..
As Mike says...the design seems to be 'in flux'....

hth
Jay

[tEaM]

Hello guys.

Thank you all for your support. Now, we'll forget the "global" project with 2304 LEDs.
I will divide the project into matrix 8x8 bi-colour LEDs. So I'll focus only on this situation:

Matrix 64 bi-colour LEDs. What is the best solution to control these matrix?


LED specifications:

Manufacturer: MULTICOMP
Manufacturer Reference: MCL039PURGW
Bulb Size: T-1 (3mm)
Forward Current / Colour: R 20mA, G 20mA
Forward Voltage / Colour: R 1.8V, G 2.1V
LED Colour: Red, Green
LED Mounting: Through Hole


Regards
tEaM

[Jerry I]

Hi tEaM

Not a very good choice of LED in may opinion, unless you want to use it in the the dark. 30/10 mcd is not very bright. you would not see this in daylight.

We would use LEDs minimum at least 1000 mcd.

Jerry

[temtronic]

one solution,
perhaps 'best',
is to buy a premade RG 8X8 module for $6 instead of 64 LEDS at .25 each($16) ! If you buy raw LEDs ,you'll have to design a PCB and pay for it. A lot of time and money, when you can easily buy 3 or 4 premade modules for the cost of 'doing it yourself'. There's a LOT of precision placement,soldering and cutting needed to make ONE module.Odds are at least 2 hours per unit IF you don't put 1 of the 64 in wrong way!! Also premade units are color/intensity matched raw LEDS aren't.
So buy premade modules.

As for the PIC, the 16F1519 looks like a nice choice, enough pins (24 for LEDS, 3 for RS485). Lots of memory,internal 16MHz should be OK for UART timing.Only costs $1 in qty .

The 'master' PIC could be a 1519 as well, very little for it to do,as the 'hard part' has been given to the PICs in the modules.

Adding in a small perfboard,connectors, etc. overall each module might cost $20.Depending on skill level,wallet and your time a working prototype could be up and running in a morning, a week would ave the project(all 32 of them) done and 'out the door'.

hth
jay

[Ttelmah]

Also, for the money it is going to cost, why not just use the WS2812 modules....
The individual LED's are 'smart', with 24bit SPI communication giving full 8bit control of each LED.
8*8 intelligent module based on these. Gives full 8bit RGB control of every LED on the module, just done as 64*24bit SPI transfers.
Only costs the same as the LED's being talked about....
Available as modules, or smart strips with 30, 60, or even 144 LED's per strip.

Caveat though, remember just how much power you are going to be talking. If you talk about 96*24 LED's. The WS2812's can draw 60mA each (and any LED that is reasonably bright is going to be at this sort of level 3LED's*20mA for each pixel). 2304*3 LED's. 6912. At 20mA each, that's 138amps peak....
Even going down to your 2*20mA LED's, each 8*8 module is going to draw up to 2.56amps. With 12*3 modules, that's over 92amps.
I've done a couple of smart panel displays, and we used over 400A supplies, with very carefully designed copper 'strip' busses running behind the boards....

[tEaM]

But I'm not building display, my friends!

I need these LED to a BIG signaling panel. The panel will have green when the switch is on and red when it's off!

[asmboy]

Reading the data sheet for the 74hc595 is instructive

source or sink 6ma per output
absolute MAX for the "hct" is just 20ma rated

your circuit as designed with a 1.2v red led vf , 220 ohm resistor
will have 16 ma per output pin and an "all on" state will exceed the chip I limit.

[temtronic]

hmmm this project keeps getting more interesting.
All along I had thought that ' 8x8 LED matrix' referred to an industry standard display module, some up to 2" square.
Now you kinda saying the LEDS will be 'somewhere' on a 'big display'. When you post a subject you should state a LOT of the overall design issues. In this case size does matter. I have a hunch it's for a model RR display to show the status of the switches on the tracks ????? If so then one again the actual electronics change dramatically.
It's one thing(easy really) to control 2000 RG LEDS in a small physical area. It's a whole HUGE problem if they are randomly arranged on a 4 by 8 foot sheet of plywood !

You should give us a precise description of the project. A modified version of the suggested SPI driven RGB LEDS has a LOT of merit for a 'big display'.

hth
jay

[Mike Walne]

[temtronic]

I'm waiting for tomorrow's 'spin' on the project !!! better than the silly cold I picked up yesterday,the PC that didn't like 13 'power failures' due to 80KPH winds or the 10 by 20 shed that isn't here anymore...might be in Kansas with Dorothy.
Good news I should be getting some 28 pin PICs to make an 8by8 matrix 'cell' tomorrow IF I can dust off the old PC and get it running...

sigh

Jay