25kHz PWM signal out of attiny85

Using Arduino Programming Questions
#1

I need to get a attiny85 to output a 25kHz PWM signal while still being able to use I2C and interrupts, but i am not sure how to do it..
I found these two threads and read through them but now i am more confused then ever.

http://forum.arduino.cc/index.php/topic,10697.0

Any help will be greatly appreciated..

#2

Code for normal Arduino boards that can generate 25kHz is available, but I don't know about the ATtiny85.

The confusing code is what is needed.
Have you seen the datasheet of the ATtiny85 ? It explains the different PWM modes and the timer registers.

Can you tell what the project is for, and why you need 25kHz and why an ATtiny85 ?
Is is to control a motor ? Or do you just want a signal of 25kHz ?
Is the ATtiny85 a Trinket ? Adafruit Trinket - Mini Microcontroller - 5V Logic : ID 1501 : $6.95 : Adafruit Industries, Unique & fun DIY electronics and kits

#3

I am trying to make a PWM PC fan controller..

My current plan is to have an attiny per fan, each will supply PWM signals and send back rpm data to an uno using I2C.
The uno will be communicating to a PC through usb so i can manage fan curves, temps, fan RPM.

I need the 25kHz PWM because the Intel specifications are a target frequency of 25kHz, with an acceptable operational range of 21 kHz to 28 kHz

I have tried reading the datasheet but I don't understand much of it.. http://www.atmel.com/Images/Atmel-2586-AVR-8-bit-Microcontroller-ATtiny25-ATtiny45-ATtiny85_Datasheet.pdf

#4

Is there anyone that can help?

#5

I'm sorry, I don't know which PWM mode should be used. I have used ATtiny chips, but not the ATtiny85.
Perhaps you can get more help at : http://www.avrfreaks.net
Do you have a schematic ? do you have a way to program the chip ? do you know which timer you want to use ?

#6