LED matrix display that scrolls whatever you want it to.

[justin hulbert]

Hi,
I’m Justin Hulbert this is my first post here I’m hoping your all just a friendly and helpful as everyone over at Parallax.

I must first say that I have yet to even buy a PICAXE yet. Since I only found out about them last night. But I have already fallen in love with them, and plan to buy a bunch ASAP. The price is just amazing and the software is so cool. I love the fact that you can test the code virtually. I also found out last night that you can use it to program basic stamps. So I tried it out, I have always dreamed of being able to code using a flow chart.

Any way I’m here about a project I want to start working on. I was going to do it with a Basic Stamp but i think i want to try and use a PICAXE Here is my idea sort of simplified.

Get or build a bunch of them large 5 x 8 LED matrixes 10 to 15 hock them together in a row. Build some sort of frame and mount them in it. Add some PICAXE chips to control the matrixes like an LCD so you can just use a serial out command. Maybe even add one of them little wireless modules. Mount It all to the wall in my room.

Now build and program some sort of controller that can receive the "text" from
the computer and send it to the LED matrix and scroll it. It would be 1000 times cooler if the “text” was an RSS feed or the song title of the song your listening to on your computer. But that would most likely be much harder to do and is a feature you could add latter.

Has anyone heard of a project like this before if so I’d love to take a look at the thing and some code? Also is it ever going to be possible for me to send an RSS Feed to the display using only a PICAXE.
Any ideas are great, since at the moment I’m just trying to figure this all out and get an idea of what ill need.

Thanks,
Justin Hulbert

 

[tikeda]

Any large matrix project will require additional chips to drive the individual LEDs in a multiplexed fashion. There are driver chips and counters/ demultiplexers available. Here are links to a couple application notes for using matrix display drivers from Maxim Integrated Products (hardware / software). They use SPI or I2C interfaces and so should work well with a Picaxe.

I found a web page (here) describing how these chips can be controlled directly from a PC's parallel port -- No need for an intermediate microprocessor.

If the display isn't too large, some Picaxes should have enough memory to hold the patterns for all the pixels in the display. Many of the LED matrix displays are formatted as 8 rows and 5 columns of LEDs, which requires 5 bytes of memory per block. Going from left to right in the display, you can map each column (= 1 byte) of pixels sequentially in memory. When you want to activate the pixels in column one, you read out the byte in memory location '1'. For the second column, read from memory location '2' & etc. Scrolling can be managed by shifting which memory location you start from when you refresh the display at column one (It's a circular buffer). So, to shift the whole display one pixel to the left, read from memory location #2 when activating the first display column.

I think it would be a million times cooler if the display scrolled through only those stocks that are going to double their value in the next six months. But I don't think the Picaxe chips have the MIPS to drive that sort of application. ;^)

Quick edit: I just found another page that describes the use of a 4017 1-of-10 decoder chip in an LED matrix display.

 

[justin hulbert]

Ok so maybe it can’t do RSS feeds, but would it still be possible to somehow catch the song title from your media player and display it.

 

[moxhamj]

Breaking it down into components:
1) Driving big led displays - yes, though you might need an eeprom to store the patterns. Only a few extra dollars and connects via the I2C bus.
2) Interfacing to a computer. Yes. See http://www.instructables.com/id/Control-real-world-devices-with-your-PC/
3) Displaying a song title. Tricky. If you can get the song title into a text file on a computer it is easy, but doing that might mean hacking into the program playing the song. If you are fine about typing it on a computer keyboard manually then this would be easy.

 

[mobents]

3: easy, with the nowplaying plugin for winamp, which lets you dump artist name and song title etc. to an xml-file. then you just need to read the info from the file into whichever language you prefer (ie. visual basic