Tobi’s Corner

What can you do with 100 common anode rgb leds? build a 8×8 matrix and interface it!

The circuit uses 74HC595 shift registers with output latch. each shiftregister interfaces one color + one shiftreg for the matrix rows. the interfaces uses 6 I/O lines for faster speed and easier interfacing. an avr running at 8MHz can update the matrix with 8 brightness levels displaying nice fading colors patterns or colored text (or both). the sample program creates fading color patterns using a sine table. for smoother display a double buffer was implemented.

Download: rgbmatrix.c

Here you can see my IKEA Storm Lamp Mod using the powerRGB circuit and the tinyRGB firmware.

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powerRGB is the extension of tinyRGB to drive high power LED’s. For this project I used a 3 x 1W common Anode RGB LED.

Q1 to Q3 are N-Channel HEXFet Mosfet’s with logic level drive and a RDSon at about 50mOhms. R1 to R3 are at about 2k2, R4 to R6 at about 15k and R7 to R9 depend on the LED used and VCC. If you use FET’s with higher RDSon you have to consider RDS in your calculation!

Rx = (Vcc-Vf)/Im - RDSon

[Vcc: Volatge of power supply, Vf: Vorward Voltage of the Diode, Im: Max current of LED]

The software for the AVR is the same as for tinyRGB.

The easiest way to control a RGB Led.

tinyRGB uses an ATMEL Attiny15L (8pin uC) to control a standard RGB Led.

R1 is a pullup Resistor for Reset generation (should be about 10k).
R3 to R5 depend on the LED you are using. You can calculate the resistor as followed:

Rx = (Vcc-Vf)/Im

[Vcc: Volatge of power supply, Vf: Vorward Voltage of the Diode, Im: Max current of LED or AVR pin (20mA)]

If you want to control power LED’s read here: powerRGB.

The software is written in Assembler (avra under Linux, should be compatible to AVR Studio). Timer0 is used to generate interrupts at about 30kHz. This interrupts are used to build a 8bit PWM. Timer1 is used to change the color pattern.

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