yes i think 512 bytes might be too much too – i was just trying to use DMX as an example of the serial message i could send. if i just send 3 color bytes per LED and let the order in which i send dictate the WHICH LED (i.e. 1st byte sets LED 1 Red; 2nd byte sets LED 1 Green; 4th byte sets LED 2, Red; etc.) that would only take 24 bytes per row – or 192 bytes for a whole ‘frame’ – that’s my theory anyway. perhaps your code needs extra data?

i saw your ‘live video’ post – that looks cool! though, i’ve got a setup that will take either custom 8 pixel animations or text or whatever and send it out to this stream of bytes.

so my question is: if i have a list of these color bytes, are there hooks in your code i could feed it into?

or to put it another way, does your code have a way to set the brightness (through PWM) of each color of a specific LED?

sorry if i’m missing something obvious. as i said, i know a little basic code, but yours is quite advanced for me – but it seemed better to adapt yours than start over from scratch. maybe not though.. = )

thanks for your time!

your code runs great and i have tweaked it a little to get different effects. what i want to do now is feed it data over serial/usb to display graphics in realtime. i was hoping this could work since the matrix would simply act as a dumb, unbuffered display, so RAM would not be an issue. it simply receives a ‘frame’ (a list of rgb values for each LED/pixel), and sets all LEDs to those levels,hopefully using your PWM code to get full color mixing. does this sound possible?

i’ve managed to send a a single BYTE over serial to set all 8 LEDs in a row to ‘off’ or ‘on’. and i could probably set this up as an array or list that would set each row. but again, this only sends 1 BIT to each LED: ON or OFF. is there a way that i could send a string or series of bytes to Arduino, that your code could interpret and set each color of each LED to an 8bit value (approximated using PWM)?

the first thing that comes to mind is something like DMX512 – the serial control protocol for lighting systems. it sends 512 bytes, each corresponding to a ‘channel’ or the brightness of a single light. for an RGB light fixture, 3 Channels or 3 bytes would set the brightness of red, green, and blue lights. the beginning of the 512 byte message is marked with a ‘header’ and repeats itself over and over at 250kbaud until a change in the message is made. the message is updated then sent repeatedly. there is a timing component, but i dont think that would be crucial in my case.

so my question is: does your code offer an elegant way of accepting data in this or a similar structure? can i pass a byte to get a corresponding brightness using the PWM part of your code? or maybe your code isn’t required? although from what i can tell your code is fast and efficient – and the use of SPI leaves some room for other operations to go on at the same time. maybe i would need this for receiving and storing the serial data? i know some code, but yours is more complex then im used to – so i can’t tell just by looking at it if there’s a way to do this.

any ideas?
thanks!
-josh

BTW. Happy New Year.

I’d be happy to hear from you again, once you’ve had some time to deal with the chips. I’ll order mine soon, but would like to hear if there are any traps to avoid.

I’ve just now measured the peak current for the red LEDs with my scope and it is about 5.5mA (1.5V voltage drop on the 270Ω resistors). That stays way below the maximum. Still you already see slight variation in brightness depending on how many LEDs are on per row. Pulling about 50mA (peak, not effective) out of a single pin is about the maximum it tolerates. For more “bang” one really needs good and fast source drivers (kind of hard to get with low turn on/off times and small V(CE)-sat.) and proper sink drivers (much easier to find and get, e.g. MBI5168, STP08CP05 – both are current regulated – or TPIC6C595 – unregulated).