Write PWM with only 8 bit? (Timer2)

Question

I have a problem with the Servo library.

I need to read a PPM signal and create a PWM signal of each channel. The problem is that PPM has a higher resolution than PWM so I want to use the 16 bit Timer1 for reading PPM. However the Servo library that writes the PWM signal also uses Timer1.

Is it possible to generate a PWM signal with 8 bit / Timer2? And has someone made an example, or an explanation about, how to do that?

• putu: Yes, there is example in this Tutorial
• Dave X: Maybe use the servo library as is, and do the PPM counting with timer2 with some overflow handling.

Answer 1

Here is a simple example from my page about timers of using Timer 2 to output a square wave of 50 kHz:

const byte LED = 3; // Timer 2 "B" output: OC2B
const long frequency = 50000L; // Hz
void setup() 
 {
 pinMode (LED, OUTPUT);
 TCCR2A = bit (WGM20) | bit (WGM21) | bit (COM2B1); // fast PWM, clear OC2B on compare
 TCCR2B = bit (WGM22) | bit (CS21); // fast PWM, prescaler of 8
 OCR2A = ((F_CPU / 8) / frequency) - 1; // zero relative 
 OCR2B = ((OCR2A + 1) / 2) - 1; // 50% duty cycle
 } // end of setup
void loop()
 {
 // do other stuff here
 }

Answer 2

Yes, Arduino Servo library uses Timer1 (and other ones, depending on Arduino boards) to manage FastPWM via software interrupts. Timer2 is used by tone() function: be careful if you are using that function.

A good example using Timer2 to generate PWM is the Infrared remote library for Arduino . If IR_USE_TIMER2 is defined it will use Timer2. The key code is at IRremote.cpp where the ISR is managed.

Answer 3

Is it possible to generate a PWM signal with 8 bit / Timer2?

yes. I implemented multiple approaches, some on avrs and some on pics but the basic principles are the same: https://dannyelectronics.wordpress.com/2017/02/18/driving-multiple-servos-off-a-pic-timer2-ranged-extended/

that post provided a list of links to other implementations - one of them off a timer 2 on avr.