> Hi, Neil.
> Beside changing the R2 position, you can use a series zener diode
> connected
> to R1 and I/O pin. I think that a 9V1 would do the trick.
> Cheers,
> Fabricio.

I've used this "zener trick" before. It has an advantage over pure
resistive level shifting in that the top of the zener still has a 5Vpp
change while the top of a resistor would not. I did a similar circuit to
PWM 5V fans with a 3.3V PIC. There, instead of a zener, I used an LED.
When the fan should be running, the LED glows.

Harold


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