UPDATE: Video link of the projet on the second page!!!
Hi guys, I don't post much here, but read as much as I can!
This is my first electronics project (other than experiments in my workshop) and I have a total n00b set of questions to ask. Hopefully, this is the correct forum for them...
An expandable/programmable LED lighting system using modular lighting boards. Each lighting board contains a 595 shift register and 8 LEDs. This component is affectionately called a ‘jixel’. There are 36 ribs each containing 12 jixels(hopefully 14 when the project is complete). So, that means 3456 (4032) bits of lighting information per frame.
The upper-dome in this picture is where the system will live.
I’m using a Mega128 to translate data coming in on USART0 onto a 40bit bus (ports A,B,C,D,F). 1 pin for each rib (36 ribs), and 3 control lines(OE, SRCLK, and RCLK). Each rib of 595s has a maximum line length of about 18 feet - from the STK500/501 where the mega lives, to the last jixel on the rib. From the STK500 to the first 595 is ~ 11 feet. After which, spacing is ~ 5”. All components are connected using 10pin ribbon cable (3V+, 3GND, 1 data, 3 control)
The OE, SRCLK, and RCLK lines are shared across all ribs. The total line length for these control lines is ~650’ I assumed line length would be a problem due to the topology of the design... I did a line length test to see how far my testing jig (a Mega32) could reliably send signals. Turned out to be ~50 feet at a 2mhz clock.
So, onto the questions...
Question 1: Obviously I need to put something on each rib to keep the signals at a good level. Since I’m a total n00b, I’m not really sure what I can use here... Would a 74HC125 do the trick?
Question 1b: If a 74HC125 is the right solution to keep the line integrity, can I just tie the OE lines active and let the buffer sit inline transparently?
Question 2: Since the serial data goes from chip to chip, the serial line shouldn’t be an issue as long as it gets to the first 595 reliably. Is this a safe assumption? I’m going to drive the serial line as well, so this isn’t really an issue (i hope), just curious.
Question 3: Obviously running all of these LEDs will require a good deal of current. Does anyone have tips on hooking up the STK500/501 board/target chip to an external power supply? The docs say just to run power to the V+ GND pins. Anything more to it than that?
Last Question: Is this project freaky enough to qualify me as a true AVR Freak?
You can find out more about the project here: http://www.jellyfish12000.com