Well, I’ve been banging my head for ways of controlling the insane number of LEDs and switches on the Defender Panel.
After a week of ideas and a lot of bits of paper being scribbled on and promptly screwed up and thrown I came up with a way forward.
I had been considering using Charlieplexing, as it uses a very low number of pins to drive a lot of LEDs (video on you tube) which seemed like a superb way of saving pins, but I was concerned about the on time of the LEDs, and with 154 LEDs to control I was concerned about the amount of flicker that would be visible.
So I’ve gone for a traditional LED multiplexing scheme. But I’ve used shift registers to control the columns, saving me lots of pins on the micro and I’ve also used a shift register for reading the switches. The other advantage of the more traditional multiplexing scheme means that the column of the switch matrix is fed from the column of the LED matrix.
The scanning of the 32 pots is also done on the same board, using 4 ADC inputs on the micro and four 4051 multiplexor chips.
All this means that instead of needing a bigger micro like the AT-Mega128 in 64pin SMD, I can use what I currently have in my ‘bits box’ which is an AT Mega32 in 40 pin DIL format. Great less cost!
I also decided to download and Eagle from Cadsoft and give that a whirl. Being a Mac user limits what PCB/Schematic CAD software is available so I was keen to give Eagle a try. I have to say, I’m really impressed. Now, ok this board isn’t exactly complex, but it is small (100mm by 80mm) and not only did Eagle have all the libraries I wanted, but it also auto-routed the entire board in around one minute. To add further joy to the proceedings, it also completely auto-routed the board! no nets left un-routed, just superb. I can see I’ll be using Eagle a lot more in the future.
The next step is ordering the PCB and few odd parts that I don’t have in my bits box. The PCB will take about two weeks to come, and the panel should be here around the same time.
One the panel is here and I’ve got some switches and pots mounted and working, I’ll take some pictures, and possibly a video (if I can find a decent camcorder).