I can understand most what they are trying to disscuss. So, I searched the forum and find some guys talking about this previously using the arduino Mega.Ĭontrolling 4-pin computer fans - PWM at 25khz? - Interfacing - Arduino Forum It is said to use the 25 kHz PWM to control the speed. void setup() =4\:MHz\).Hi, I want to use Arduino Micro to control the speed of a 4 wire compurter fan. The register OCR1A is set to 127, which results in a duty cycle of 50%. The waveform generation mode is set to 8-bit Fast-PWM, which means that the top value of the counter is 255, and the compare output mode is set to non-inverting mode on Arduino pin 6. It uses no prescaler to get the maximum frequency. The following example should illustrate the basic concept. Set OC1A/OC1B to HIGH on match (inverted mode) The bits COM1A1/COM1A0 and COM1B1/COM1B0 determine what happens to the respective output in case of a match between counter and OCR1. On every increment the value of the counter is compared to the value in the register OCR1A (for pin OC1A, Arduino pin 6) or OCR1B (for pin OC1B, Arduino pin 5). WGM13:10Įvery timer increments its counter from 0 to the top value, which is determined by the waveform generation mode. There are 16 different waveform generation modes for Timer1, but I will describe only a small selection here. The waveform generation mode determines the top limit of the counter and the waveform generated at the output pin. Timer0 on the Attiny84 has an 8-bit and Timer1 a 10-bit counter. CS12Įvery timer has a counter, which is incremented on every tick of the timer. The prescaler is set with the bits CS12, CS11 and CS10. With a prescaler of 256 the timer ticks once for every 256 CPU clock ticks. The prescaler divides the CPU clock frequency into smaller chunks. With no prescaler enabled, the timer ticks at the full speed of the CPU clock frequency, which is usually too high for any practical purposes. This looks very complicated, but it is actually quite easy if you read the datasheet. The following table shows all the bits for the registers TCCR1A and TCCR1B. By setting and unsetting the bits in these registers, we can control the behavior of the timer. These registers are called "Timer/Counter Control Register" or TCCR for short. Register DescriptionĮvery timer has two registers to set its mode of operation. Timer0 works essentially the same, with some minor differences, which are outlined in the datasheet. For the sake of brevity I will describe only the configuration of Timer1 in this post. So by changing the frequency of Timer0 a lot of libraries will stop working correctly. Timer0 is used by the Arduino environment for timing functions like delay(), millis() and micros() and many libraries depend on these. The pins 5 and 6 (Arduino digital pins 8 and 7 respectively) are controlled by Timer0 and the pins 7 and 8 (Arduino digital pins 6 and 5 respectively) are controlled by Timer1. The Attiny84 has two timers called Timer0 and Timer1 and four PWM pins. All this information can be obtained by reading the datasheet for the particular chip. Every PWM-pin is controlled by a certain timer and different chips have different timers. On the Attiny84 and other Atmel chips only certain pins can be used for PWM output. This post shows how to set these flags and how to create really high frequencies like 4 MHz. To change the frequency, you have to set the appropriate flags in the Attinys registers manually. The default frequency seems to be either 250 Hz or 500 Hz, which is clearly not enough for certain use cases. The problem is, that you cannot set the frequency of the output square wave. The variable dut圜ycle can be set to a value between 0 and 255, whereby 0 means the pin is always off and 255 means it's always on. The Arduino API allows you to use PWM and set the duty cycle with the function analogWrite(), which also works on the Attiny84: byte PWM_PIN = 6 This relation is given as a percentage and is called the duty cycle. The power supplied to the device is determined by the length of time the pin is on versus off. It works by switching a digital pin on and off at a high frequency. Pulse-width modulation can be used by a microcontroller to control the power supplied to other devices like LEDs or motors. How to set the PWM-frequency for the Attiny84 Author Andreas Rohner Date Tue Category Electronics How to set the PWM-frequency for the Attiny84 My Notebook
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