DMD PWM

The Dot Matrix Display (DMD) is a 32x16 array of high-brightness LEDs for visually striking effects. [Product Page]
milamber
Posts: 12
Joined: Wed Mar 14, 2012 7:08 am

DMD PWM

Post by milamber » Wed Mar 14, 2012 8:06 am

Hello,

I am very interested in using multiple DMD's to create a Large outdoor display. (Christmas light project :) )
I have been working on building an LED matrix by hand and although I have it working, it was VERY time consuming to create. Using a Library on the Arduino forum I was able to create a mini streaming video display. This library was written to allow Shift Registers to do PWM. The library is called ShiftMatrixPWM and was created by ElcoJacobs.
Original thread: http://arduino.cc/forum/index.php/topic,66988.0.html
Post with most upto date library: http://arduino.cc/forum/index.php/topic ... #msg536032

This library allowed me to create a 16x16 RGB display that could display streaming video at 15fps with 32 brightness levels per colour. In Mono that would be a 48x16 display (more than a single DMD). This was all being run by the Arduino and I have been trying to port the library so it would work with a DMD.

Unfortunately I am still relatively new to Arduino and microcontrollers. My attempts at converting it have not worked at all. I will continue to try but if someone more knowledgeable wants to have a look at this library and have a go at writing something similar for the DMD that would be awesome. I only post it here in case others are interested in trying to get PWM on the DMD. And it might give them some pointers on a way of accomplishing it.

Here is a video of the 16x16 RGB in action:
http://vimeo.com/31318436

Thanks!

maverick25ss
Posts: 13
Joined: Wed Mar 21, 2012 4:03 am

Re: DMD PWM

Post by maverick25ss » Wed Mar 21, 2012 4:14 am

I am also interested in PWM on this display, but more for just dimming it. They weren't wrong when they said this thing was bright!! I noticed the PWM pin on the connector board (unless that is the name of the arduino pin, not the pin for the display) and was just wondering if this is a coincidence or it may be dimmable.

debenham
Posts: 33
Joined: Tue Jan 10, 2012 3:22 am

Re: DMD PWM

Post by debenham » Mon Mar 26, 2012 2:11 am

My version of the DMD library does support grayscale/PWM (see other thread in this forum for details or http://www.adebenham.com/category/arduino/dmd/ )
Some more work needs to be done to get it working nicer but should be a good starting point.

maverick25ss
Posts: 13
Joined: Wed Mar 21, 2012 4:03 am

Re: DMD PWM

Post by maverick25ss » Sun Apr 01, 2012 6:26 am

I wish I had that sort of time to 'throw something together'. The more I see people using more than one I'm tempted to get another, or two.

Its all good. I don't know why it didn't work before but I can now hook the DMD to my eleven or etherten and the display lights up dim, which is what I was after. This will do for now.

milamber
Posts: 12
Joined: Wed Mar 14, 2012 7:08 am

Re: DMD PWM

Post by milamber » Wed Apr 04, 2012 7:22 am

Well I had a block of time to look at this with a fresh set of eyes. And this time I have had some success. I was able to modify the original library so that is now able to output in the correct way for this display. Unfortunately it is no where near perfect (or even very usable) at this point.

It is able to output to the display and address each individual pixel but it was written to interact with a very different hardware setup. This means although individual pixels are being addressed they are in completely the wrong order!

So the methodology for the PWM and outputting to the display works. I just need to get the data order correct.

Hopefully I will have some more time soon to try and achieve this.

milamber
Posts: 12
Joined: Wed Mar 14, 2012 7:08 am

Re: DMD PWM

Post by milamber » Sun Apr 08, 2012 3:05 pm

OK it works!

I am pretty sure I have used a hammer to put in a thumbtack though. The code is NOT pretty but it does work. I have modified the library from the first post to work with the DMD. I currently have it doing some tests. Seems to be working fine with 32 Brightness levels. The PWM shows up the best in High Power mode.....otherwise its difficult to see all the levels.

I am going to try and clean up the code before I post it. I really have gutted the library and hammered it into place to make it work. It implements the addressable PWM and that is it. It has no other functions.

I just got a second DMD today so I will see if I can get it to work across two of them. I don't think it will support any more than that!

If anyone is super interested and wants to see the code. Let me know and I will see what I can do.

cef
Freetronics Staff
Freetronics Staff
Posts: 106
Joined: Wed Nov 09, 2011 12:53 am

Re: DMD PWM

Post by cef » Mon Apr 09, 2012 2:50 am

If you check out this DMD thread, you'll see that debenham changed a value that improved the speed of addressing across multiple DMD's. This change may give you enough overhead to drive more displays with your code as well.

User avatar
jonoxer
Freetronics Staff
Freetronics Staff
Posts: 297
Joined: Sat Oct 15, 2011 11:31 am

Re: DMD PWM

Post by jonoxer » Mon Apr 09, 2012 12:14 pm

Hey @milamber, that sounds like a pretty cool achievement. Any chance you could post a video or something so we can see how it turned out?
--
Jon

milamber
Posts: 12
Joined: Wed Mar 14, 2012 7:08 am

Re: DMD PWM

Post by milamber » Mon Apr 09, 2012 9:58 pm

I just really quickly took two short videos. They were shot close to the DMD which was in low power mode (otherwise WAY to bright for the camera).
http://vimeo.com/40036133

and

http://vimeo.com/40036316

User avatar
jonoxer
Freetronics Staff
Freetronics Staff
Posts: 297
Joined: Sat Oct 15, 2011 11:31 am

Re: DMD PWM

Post by jonoxer » Tue Apr 10, 2012 1:08 pm

That's great! Thanks for posting the vids. Do you mind if I do a blog post and feature them?

Also, what were you feeding to the display? Was it a random pattern, or images, or some sort of video feed? If I sit back and squint at the first video I imagine I can see faces and things in it, but I don't know if that's just my brain reading more into it than is really there.
--
Jon

Post Reply

Who is online

Users browsing this forum: No registered users and 4 guests