Lightboard project - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: June 10, 2013, 01:06:47 am
content: So here's the project I've been working on.I had a 80x7 lightboard I bought a while ago - but I never liked its functionality. When I took it apart, I found that there were two boards (I'll post pictures of these when I get a chance to take it apart) - a controller board, and the display board, connected by a 20 pin header. So after a few false starts, I took the controller board off, set it aside, and set to reverse engineering the display board.It turned out to be a pretty typical setup - 20 74595 shift registers for the row, alternating in color (one byte for green, one byte for red, repeat). There was a 74138 for row driving, the actual LEDs being driven by four dual mosfets. I blew one of the mosfets out, so after having ordered another one and replacing it (a tricky bit of smd work that I'm still surprised I managed to do considering my inexperience at the time) I got everything to working.So I took an arduino mega and built a shield for it. The shield currently has a 20 pin header for the display, a 6 pin molex header for the VFD display (and a MAX232 to drive that), and a 34 pin header for the interface to the mega, along with a small 8 pin header for the serial1 output. And, it works. Once I figured the hardware out, I wrote all of the necessary code to get it to scan the rows and display characters (it heavily, heavily leverages the interrupt capabilities of the atmega2560), wrote the routines to display status output on the VFD, and a serial command line interface so I can tell the lightboard what to display by opening a serial console to the arduino. You can see "plainorange" - that is the mode the board is in. I'm going to add modes such as "scroll", "random", etc. I wrote the code such that adding new modes is relatively easy. D means "debug", when it's set to 1, those four dashes on the right turn into a display of the amount of free memory. That's kind of expensive, so it's off by default. The mode is "ready" or "wait" - it's set to wait when the self test is running.I have a bunch of todos - I want to add a USB or PS/2 keyboard interface so I don't need a computer to operate it at all, for example - but most importantly I want to create a custom controller board (custom arduino) that plugs right into the display board rather than needing a separate box to drive it - with a port for the programmer box, along with keyboard, etc. That is going to be my first PCB project.Pictures below. I got pictures of everything but the lightboard in operation - it works, but I didn't have an easy place to plug it in.If you want to see the code, that can be arranged. I'm more of a software developer than hardware guy anyway, so I tend to go for code when I have the option. If you're interested in seeing any other aspects, such as the display board, let me know too, that can also be arranged. I just wanted to show off the parts that I did.

author: David_AVD
author_rank: Super Contributor
timestamp: June 10, 2013, 01:13:49 am
content: Good work.I have a couple of dot matrix LED displays (one is red and the other is red/green) that I want to fiddle around with at some stage. A lot of these display use '595 shift registers and ULN driver chips for the columns. Some have weird ways to do the row addressing though.

author: Unknown
author_rank: Unknown
timestamp: June 10, 2013, 01:17:08 am
content: Let me know if you need any of my work to stand on the shoulders of. I'm not going to claim it's the best out there, but it works.

author: David_AVD
author_rank: Super Contributor
timestamp: June 10, 2013, 01:21:20 am
content: I don't have a pressing need for those displays at the moment. They are just there sitting on the shelf waiting for the day I find a good use for them. I have a lot of stuff like that!

author: Unknown
author_rank: Unknown
timestamp: June 10, 2013, 01:23:16 am
content: I don't have a need for it either, it's just a fun project to get my feet wet. It's the project I used to prove to myself I could do it and break through many years of programmed discouragement.

author: David_AVD
author_rank: Super Contributor
timestamp: June 10, 2013, 01:34:03 am
content: Sometimes a seemingly "useless" project teaches you something that proves to be very useful later down the track.

author: Unknown
author_rank: Unknown
timestamp: June 10, 2013, 01:39:00 am
content: Yeah, that's why I'm spending so much time with it. It's teaching me useful stuff, and it's about to teach me how to build a PCB and assemble it using reflow techniques.