8 years, 10 months ago.

How to use

Hi, sorry for my very newbie question. I have created a mbed project, and added both files to my project.

I then included the .h file in my main.cpp file.

In my main function I added "PwmIn(PA_3);" but the compiler gives me an error as follows; Error: No default constructor exists for class "PwmIn" in "main.cpp", Line: 30, Col: 12

Can someone tell me what is wrong? I Clicked on the help link in the compiler and I don't understand what is wrong or what it is telling me.

What I would like is to add up to 6 RC inputs to my Nucleo STM32F411 board.


Question relating to:

Code to read a PPM/PWM pulse, interrupt driven. Most useful for RC receivers. Code is non-blocking, and a poll of the stall timer can detect if a signal has been … interrupt, PPM, pwm, RC, Receiver


posted by Adrian Rusu 13 Nov 2015

2 Answers

8 years, 10 months ago.


PwmIn myPwmIn(PA_3);

You make an object (myPwmIn, or any other name you like), of type PwmIn.

Accepted Answer

Hi Eric, after lots more searching I ended up finding exactly what you suggested. I found it in someones code for a tug boat (sorry tugboat author, I don't recall your name).

posted by Glendon Turner 03 Sep 2015
8 years, 10 months ago.

Hi Glendon,

Can you post your code?

To use the PwmInRC library, it's pretty easy:

1) Import the ORIGINAL library by Simon Ford. My library one has been modified with a WDT in case my quadcopter lost link to my transmitter.

2) Declare the prototype:


PwmInRC rxModules[5] = {p14, p15, p16, p17, p18};

3) If you are polling:


RXPolled = rxModules[0].pulsewidth(); 

If you want your pulsewidth to be completely interrupt driven, you should modify the PwmInRC library accordingly to obtain the pulsewidth based on the interrupt action instead of a poll. However, you must consider mutex/semaphores for the RTOS to be fully compliant, as well ask keeping the ISR efficient.

Good luck, Ian =]

Hi Ian, I ended up working out what Eric mentioned here, but I am now more interested in your answer.

It seems like your library PwmInRC is different to PwmIn if I am not mistaken? I would like to use a WDT as well, for safety reasons (it's not a quadcopter though). I am not using an RTOS (zero experience with these) but have thought about it. Just don't think I know enough about the basics yet. I don't understand your prototype, why is it needed, where does it go, what is p14 etc. I think your 'Use' entry means the variable RXPolled will capture and contain a single pulsewidth each time I call it, is that correct? I envisage I need an update rate on multiple channels around 10Hz (every 100mS). Thanks very much for your post.

posted by Glendon Turner 03 Sep 2015