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Forum Index : Microcontroller and PC projects : Could the Micromite +

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lew247

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Joined: 23/12/2015
Location: United Kingdom
Posts: 1702
Posted: 05:30am 24 Apr 2016
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Could it drive one of THESE 32X64 rgb displays?

Anyone driven it or fancy having a go?
I just bought one, I have an idea what I'd like to do with it, which doesn't involve fancy graphics or anything, just mainly words with some characters displayed on it but I suspect it might need something like C Function to get it going right which I wouldn't have a clue how to do it.

I did find information about the display HERE. There are several pages going through how to connect to it and how to talk to it and so on, it's written for an arduino but I really think the Micromite+ should be able to run it without a problem.
Well without much of a problem anyway :)

Edited by lew247 2016-04-25
 
palcal

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Joined: 12/10/2011
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Posted: 11:57am 24 Apr 2016
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Hi Lew,
Have you had a look at the Mik-Matrix. BigMik designed the hardware and Justplayin has written the code. It's not as big as the one you bought but I have been testing it and it has a lot of features.
Paul.

Edit.... I posted before I had a look at the display on EBay, I don't know if I understand what it is. It says it is HD video and then says it is 32X64 LED matrix.Edited by palcal 2016-04-25
"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"
 
bigmik

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Joined: 20/06/2011
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Posted: 02:55pm 24 Apr 2016
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Hi Lew,

I have been looking at those modules with envy for a while now, and they are relatively cheap seeing they are RGB.. I am sure someone with the smarts could write CFunctions for one of these.

Be aware that they are pretty hungry on current draw, I suspect that they don't multiplex the LEDs and that when they are on they are on 100% duty cycle.

The pictures, on ebay, are very misleading as you could NEVER get as high a resolution as they show.. You would need a wall the size of a hanger to get that resolution and a 100mm dia. power lead to drive it.

We have walls, at work, about 6m x 3m size and as impressive as they are, you can still see the individual LEDs at about 20m away, they are not like viewing a TV screen, although they do a good enough job.

Anyway an interesting idea I hope someone with the programming skills gets bitten by the curiosity bug.

Kind Regards,

Mick


Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
MicroBlocks

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Joined: 12/05/2012
Location: Thailand
Posts: 2209
Posted: 05:32pm 24 Apr 2016
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They are multiplexed and not easy to drive.
You need to use PWM (for every single pixel!) to get more then eight colors.
In practice that means you would need to build a table in memory and send it to the display as fast as possible. A 80Mhz chip would be ok, but from basic or even a CFunction it is as good as impossible. A CFunction could certainly drive it but it would spend so much time keeping the display updated that not much time is left for anything else.

Best approach is to use an FPGA or very fast mcu with some extra driver chips and dedicate it to update the display and receive the text to display over i2c/spi/serial

Microblocks. Build with logic.
 
lew247

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Posted: 09:40pm 24 Apr 2016
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Thanks
looks like it's one of those things that I'll put away for another day, I'll have to think about it sometime in the future, I'm still a newbie when it comes to Micromite, I would have no hope with an FPGA.
 
lew247

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Posted: 08:16am 15 May 2016
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In case someone wants to "have a go" at these - this "might" help

Information from ADAFRUIT who have also written code to get the display working.
https://learn.adafruit.com/32x16-32x32-rgb-led-matrix/




UPPER RGB DATA




Pins R1, G1 and B1 (labeled R0, B0 and G0 on some matrices) deliver data to the top half of the display.


LOWER RGB DATA



Pins R2, G2 and B2 (labeled R1, G1 and B1 on some matrices) deliver data to the bottom half of the display.

ROW SELECT LINES




Pins A, B, C and D select which two rows of the display are currently lit. (32x16 matrices don’t have a “D” pin — it’s connected to ground instead.)


LATCH WIRE



The LAT (latch) signal marks the end of a row of data.


CLK WIRE



The CLK (clock) signal marks the arrival of each bit of data.


OUTPUT ENABLE WIRE (OE)



OE (output enable) switches the LEDs off when transitioning from one row to the next.




GROUND WIRES

https://cdn-learn.adafruit.com/assets/assets/000/023/844/medium640/led_matrix_plug-gnds.png


32x32 and 64x32 matrices require three ground connections. 32x16 matrices have four.



How the Matrix Works by Phillip Burgess

There's zero documention out there on how these matrices work, and no public datasheets or spec sheets so we are going to try to document how they work.

First thing to notice is that there are 512 RGB LEDs in a 16x32 matrix. Like pretty much every matrix out there, you can't drive all 512 at once. One reason is that would require a lot of current, another reason is that it would be really expensive to have so many pins. Instead, the matrix is divided into 8 interleaved sections/strips. The first section is the 1st 'line' and the 9th 'line' (32 x 2 RGB LEDs = 64 RGB LEDs), the second is the 2nd and 10th line, etc until the last section which is the 7th and 16th line. You might be asking, why are the lines paired this way? wouldnt it be nicer to have the first section be the 1st and 2nd line, then 3rd and 4th, until the 15th and 16th? The reason they do it this way is so that the lines are interleaved and look better when refreshed, otherwise we'd see the stripes more clearly.

So, on the PCB is 12 LED driver chips. These are like 74HC595s but they have 16 outputs and they are constant current. 16 outputs * 12 chips = 192 LEDs that can be controlled at once, and 64 * 3 (R G and B) = 192. So now the design comes together: You have 192 outputs that can control one line at a time, with each of 192 R, G and B LEDs either on or off. The controller (say an FPGA or microcontroller) selects which section to currently draw (using A, B, and C address pins - 3 bits can have 8 values). Once the address is set, the controller clocks out 192 bits of data (24 bytes) and latches it. Then it increments the address and clocks out another 192 bits, etc until it gets to address #7, then it sets the address back to #0

The only downside of this technique is that despite being very simple and fast, it has no PWM control built in! The controller can only set the LEDs on or off. So what do you do when you want full color? You actually need to draw the entire matrix over and over again at very high speeds to PWM the matrix manually. For that reason, you need to have a very fast controller (50 MHz is a minimum) if you want to do a lot of colors and motion video and have it look good.

How quickly can we feed data to the matrix? Forum users Andrew Silverman and Ryan Brown have been posting their progress driving the 16x32 matrix with an FPGA, and the limit appears to be somewhere between 40 and 50 MHz. Ryan writes: “I haven't validated 100% pixel correctness, but 50 MHz seems to work for me […] 67MHz definitely did not work.” He also provided this graph showing current draw relative to clock frequency:





“Notice that the LED panel current consumption decreases as clock frequency increases. This suggests that the LED ‘on time’ is decreasing. I’m guessing this is caused by frequency-invariant delays in the LED driver shift registers.”



Edited by lew247 2016-05-16
 
lew247

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Posts: 1702
Posted: 08:25am 15 May 2016
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Shame it needs 6 pins for RGB, (upper R, Upper G, Upper B, Lower R, Lower G and Lower B) as the Micromite has only 5 PWM outputs which I'm guessing could have been used to drive this display???

It also needs 5V to drive it but that isn't a huge problemEdited by lew247 2016-05-16
 
bigmik

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Posted: 01:47pm 15 May 2016
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GDay Lew, All,

Could you not tie both reds, both greens and both Blues together so you only have 3 colour's to chose from (OK only 8 colours) but it will allow you to work on some code, if it proves successful you then try to think outside the square for a solution..

Kind Regards,

Mick
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
bigmik

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Posted: 02:10pm 15 May 2016
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Hi Lew,

I might be terribly wrong here, but I think you might be better off looking at an intermediary board such as this one.

RGB CONTROLLER

I have no real information on how to implement this but it is giving you food for thought.

Kind Regards,

Mick

EDIT *** Sorry posted incorrect link... Fixed now

MickEdited by bigmik 2016-05-17
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
lew247

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Joined: 23/12/2015
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Posts: 1702
Posted: 10:49pm 15 May 2016
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That is a brilliant idea, I'm sure something like that could probably work
Definitely food for thought at some stage
However the one you posted is only a single colour *I think* but they do rgb ones, just more expensive

I've got one of the RGB panels, but I'm in no hurry to do anything with it, after the weather station is finished your Mik-Matrix is the next project
 
bigmik

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Posted: 11:19pm 15 May 2016
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Hi Lew,

I did initially post the wrong link but I edited it to point to what I think is a colour unit the specs state FULL colour and then in the details it states 32x512 rgb

Use the link in the post, not the initial email you got as that WAS mono.

Mik
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
lew247

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Joined: 23/12/2015
Location: United Kingdom
Posts: 1702
Posted: 07:26am 04 Jun 2016
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In case anyone has one of these modules you might find THIS PAGE very interesting
 
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