Revisiting ATtiny85 Software-Based PWM to Drive RGB LED
I’m digging up some old code that I did a long time ago - It’s a software-based pulse width modulator (PWM) for AVR microprocessors. The basics came from this technote, and the code was based on this sample project from AVR.
I originally wanted to have this run 2 RGB LEDs from an ATtiny85 but I steered away from that because I was going to have to use the reset pin as an output and then I ran across this in the ATtiny datasheet - Table 21-1, page 162:
6. The RESET pin must tolerate high voltages when entering and operating in programming modes and, as a consequence, has a weak drive strength as compared to regular I/O pins. See Figure 22-23, Figure 22-24, Figure 22-25, and Figure 22-26 (starting on page 184).
Looks like I can’t drive an LED with the reset as an output directly. Bummer. No big deal using a bigger (more pins) AVR chip, but I thought it was cool to get two PWM-ed RGB LEDs out of an 8-pin chip.