Want to learn about PWM for SPI type RGB LED display

[tdg8934]

These Absen-OF20v 16x8 pixel RGB modules were given to me to develop with from my client as a test to see if it can be done with a micro-controller to replace some bad software interfaces originally designed my Chinese manafacturers. Since the Receiving card and "Full Color" controller card interfaced to the modules and PC, it was asked of me to find another way to eventually have better software (written by his software developers), talk to my micro-controller and associated hardware.

If you go to this link you will see the modules arranged in 6x4 configurations in cabinets at about $2900 each. Many cabinents are then cascaded to make up the large display signs you see outdoors. This is not my client but just another US distributor I found on the web: **broken link removed**
The "Full Color" LED Display controller PCI card is also shown but not the "Receiving Card". This is only referenced in the Installation manual. This could be the key element here.

I bought microElectronica BASIC with an EasyPIC 4 (now up to the EasyPIC 5) about a year ago and I returned it because I was confused with it intially and saw the BASIC was not as large in commands as SXB was for the Parallax SX chips that I was currently using. I can probably go back to this if you think this is the "right" way to go on this with available PWM, RAM, etc.
https://www.mikroe.com/en/tools/easypic5/

Parallax SXB for their SX chips is far more advanced than their BASIC STAMP 2's. You can insert in-line assembly (which I don't know too well) as well as a large command of BASIC like SXB statements.

Can the PIC meet this challenge or stick with my current comfort zone of experience with the SX chips?

**broken link removed**

 

[SMUGangsta]

id stay in your comfort zone at least until you get one of the modules working properly, then try 2 - and when you run out of 'time' sending your commands to the module, then upgrade to something faster/more suitable.

 

[tdg8934]

Currently as shown in the pictures. I have 2 modules cascaded together as my code reflects this for a full 2 * 16x8 OR 16x16 size display. It may not be evident when looking at the pictures that this is acually 2 of them. See attached pictures.

But the concern still is how do I do PWM with this board an an SX chip?

 

[blueroomelectronics]

Not likely a simple SX series microcontroller can replace the somewhat more complex $800 PCI controller seen in this photo. Seems like a fair amount of RAM. What's the Ethernet (dual?) for? And the RJ45? and what looks like a DVI connector? Which ones go to the display?
**broken link removed**

 

[SMUGangsta]

hi blueroom, have a look at the datasheets in page 1, it shows the various connections between parts.

I was thinking the same about processing power, but the sx deffo has the power for atleast 4 panels - which is a good start because the logic involved will be sorted - and will be the same regardless of which chip is used.

I think we are very very close!

I will build one of these (it will be crude and only 8x8), based on 4 MAx7219 chips, which will emulate your system exactly - and I will write some code to show you how to vary the brightness of individual bulbs, eg make more colours

It will take me a few days to get LEDS ect in

 

[blueroomelectronics]

The datasheets for the PCI card or the module? The module is just a big shift register far as I can tell.

 

[SMUGangsta]

one of them is like an installation manual.

But your right about it being a shift register, the module is basically 8 MAX7219's - 2 forr red, 1 for blue, 1 for green (x2 for upper and lower)

Which i am comfortable with, I use them for everything!!

 

[blueroomelectronics]

I'm looking at making a PCB for an SPI maxim 10x14 array. And yes if you plan on doing full color the SX will not keep up. The OP is probably going to require something fast with external SRAM like an ARM.

 

[tdg8934]

Blueroomelectronics,

I have attached at what I think is a manual/datasheet "something" for the "Full Color" LED Display Controller card. I believe it would be the "L2003T" (see page 2 - 1.2 Packaging List). I could be off on this, but links to links took me here and it "looks like it is right". I think it is refered to as a "Sending Card". It briefly mentions the "Receiving Card" (this is the card that has ethernet that connects to the Absen modules directly). I have no other information about the Receiving card. My client "may" be able to ship me a receiving card and sending card in a couple of weeks to borrow to examine and ship back.

SMUGansta,

I will build one of these (it will be crude and only 8x8), based on 4 MAx7219 chips, which will emulate your system exactly - and I will write some code to show you how to vary the brightness of individual bulbs, eg make more colours

It will take me a few days to get LEDS ect in

I have worked with the MAX7219 many times with the Basic Stamp 2 and with SX28 chips. I was the one that worked on figuring out how to cascade them on the SX28 on the Parallax forum. I would like to build this along with you as I have lots of the MAX7219 ICs. However, I have used cascading MAX7219's with "MATRIX" 8x8 LED displays (for the 64 outputs). Are you using a matrix becuase this would not emulate SPI? I have plenty of 8x8 matrix chips (in bi-color too). Also have plenty of LEDs. Let me know how to proceed. Can you explain why you are using 4 MAX7219 ICs? My guess is that 1 will be for each LED color (Red, Red2, Green, Blue). Right? If so is, it necessary to just dupplicate this 4 times (or are you trying a load test or something). What micro-controller are you going to use (an SX28 , a PIC, an AVR ?)

I'm very excited about this and want to follow along!

Thanks so much.

 

[SMUGangsta]

the reason for the 4 max7219s is to emulate 4 streams in the same way that your module does (yours uses 8) cos of top and bottom, or to be more specific i will be emulating R1A R1B G1 B1.

I will lay out my matrix as best as I can to emulate your module using the zigzag pattern.

 

[tdg8934]

Use this Excel based Tile Calculator. It puts the data into the right format for you to copy and paste it into DATA statements. I had to ZIP it to attach it as a file. If you open up the entire screen you will see a message telling you to copy and paste the farthest to the right side DATA statements and bit data to the SX program. It is separated to work with 2 Absen modules.

Just click on the Black or White blocks and change them from 0 to 1 or vice versa and watch the DATA statements change in real time.

Eventually I wanted to have the SX28 do this conversion in the future but for now I have this and it works ok for 16x8 screens.

 

[Mike - K8LH]

Quick question, please?

Anyone know why there are two red LEDs in each RGB pixel on these particular 8x16 modules?

 

[tdg8934]

All I was able to find out is that the 2nd RED adjacent LED is called the Virtual Pixel. I beleive it adds additional color depth to go beyond 24 bit and double the resolution effect.

Issues #4/2004 Virtual pixel: Promotional trick or image improvement

 

[SMUGangsta]

so for the purposes of this (at the moment), we could ignore the 2nd RED led.

do you have any info on the led types used - eg brightness, wavelength, etc so I can get something similar to yours?

 

[tdg8934]

The Absen module Datasheet (2nd page - attached) has all the LED specifications:

Brightness: 5500 (mcd - I am assuming) +- 10% Nit (not sure what "Nit" is)
Wavelengths: Red: 620-635nm, Green: 515-530 nm, Blue: 460-475nm

 

[tdg8934]

Here is a Parallax SX28 micro-controller program that I converted from a Parallax Basic Stamp 2 program. It cascades (2) MAX7219 LED driver ICs that use (2) 8x8 LED Matrixs. In my case I beleive I used it with (1) bi-color 8x8 LED Matrix - but can't remember for sure.

Hopefully a variation of this can be used for the similuation of the Absen 16x8 RGB LED module(s).

It is normally labeled as *.sxb but I had to rename it as *.txt to attach it here.

 

[tdg8934]

SMUGansta,

I have been given permission to "loan" you one of these Absen cards due to them being expensive (loan) and your willingness to help me out (trust). If you think this would help please email me your address and requirements. I understand that you are in the U.K. so shipping may be expensive. Do you have the capability to make a 16 pin IDC cable? I can probably make something up and ship it to you if you do not. I am putting my trust and reputation in the return of the card. My email is gilmoret@us.saic.com

Let me know if you would like a loaner module or if you want to go with the MAX7219 approach.

Thanks for your help.

Tim Gilmore

 

[SMUGangsta]

Hi tim

That would be great, as its very difficult to explain things then have you try it, then report the results and repeat.

I will PM over all my details.

I do have 16way ribbon cable here, as well as idc connectors so that should be fine.

Let me know, hopefully we'll have this working just shortly.

 

[tdg8934]

I got your PM and details. I could not see how to PM you originally.

I'm so glad you are willing to help. If you get it working well and it doesn't for some reason translate over to the SX28 (which I'm sure it will), then perhaps I will go back to MikroElectronica Basic again and buy that with an Easy PIC 5. But of course I will shoot for what I know - SXB.

I will go to the post office tomorrow and hopefully ship it out to you to get next week. I'm glad you have a cable, as I would ship you mine but I would then have to wait for my client to ship me some new parts (including more IDC connectors and ribbon cable as I am running very low) next week.

I will discuss return shipping at a later date. Don't worry as you will be re-imbursed or we will figure a way to make it easy and no end cost to you.

Thanks again!

 

[SMUGangsta]

just an update to let you know that I havnt forgot about it.

today i have been mostly building... a dataconverter/drawing package for the module when it arrives, just now it is set to 12bit colour (4096 colours). you can draw on the picture, load, save etc and you can preview as it will appear on the module (remember you need to be atleast 14 meters away from the module for best results - same here! lols) there are a few preview sizes to make life easier, aswell as RGB previews for top and bottom channels.

By tomorrow morning I should have the output data too, but I have to go out in a bit and dont want to start then leave halfway through.