RGB LED Matrix V3

Just a short demo of the new hardware.

Category:

Science & Technology

Tags:

• arduino
• electronics
• DIY
• AVR
• LED
• RGB
• matrix
• linux

[mikey6879]

May i ask, how you program the colour change on rgb leds?

[zupnikal]

@mikey6879: by hand ;-)

Just like in old-fashioned cathode ray tv sets, the 'screen' is scanned row by row.During the time each row is processed it essentially boils down to a counter running, against which the desired brightness of each colour is compared. Once the counter is greater than said value(s), the led is turned off. This produces a square PWM signal. By changing the duty-cycle the base colours are changed. The static image relies on persistence of vision. The C-code is on my blog.

[mrmikerotch]

I wonder if I could use something like that to drive an electronic typewriter...

[zupnikal]

@mrmikerotch: Maybe. Simulating key presses sound like a lot of wires, but should work. If you're lucky, it's got a serial interface.

[mrmikerotch]

@zupnikal It's an 8IN 8OUT style keyboard matrix, so it shouldn't be too bad. It does have a serial interface, but the type protocol is ridiculous. As best I can tell from probing, it has three 8-bit reg's for serial control. Two are for stepper drivers (yes, you have to program the freakin' stepper sequence externally) and the last reg is for the daisy wheel. Also, the last bit of the register is the strike bit, so the characters are 7-bit. Which means I no ASCII.

[zupnikal]

@mrmikerotch: So if you use it the normal way it advances by 1 letter automatically, if you send data over the wire you need to send the actual high/low sequence for the coils? That's hilarious.

[horlacsd]

Wikkid shield! 

[mrmikerotch]

cont... I think it may have been made this way to avoid using some more expensive chips. Any '80's guys out there? Also, I totally noobed myself back there. When I first said serial interface, I meant parallel. Sorry for any confusion.

[mrmikerotch]

@zupnikal I have been doing some more poking around, and I'm starting to think that the "interface" is multiplexing the stepper driver for the carriage with the letter selection as binary. When I took the first three bits and cycled them in phase, I was able to move the carriage back and forth, and the next four are the first four bits for letter selection. I thought that the last line was a "strike" pulse, but now I think it is a multiplex clock.

[daxweb]

great project