2 Replies Latest reply on Nov 15, 2018 6:48 PM by roowc_263906

    How do I measure a PWM duty cycle from a servo signal?

      Background story:  I built a 3d printed excavator arm for my son for christmas a couple years back (https://www.thingiverse.com/thing:2041143) and he broke the lame servo I put on it, so I redesigned the connection for a stepper, but instead of reprogramming the psoc 1 that runs the controls, I'm going to put in a psoc4 to intercept the servo output from the psoc 1 and control the stepper motor.  It should be easy and a good excuse to put one of the red boards in the box...


      Problem: I'm using a psoc 4 4200 protoboard to intercept a PWM servo signal and drive a stepper motor, but I can't get the timer interrupt to trigger on the rising/falling edge of the signal.  I've read Re: Measuring 8 Hobby Servo Signals downloaded the example 1 servo project and watched the psoc 101 tutorials on how to use the TCPWM component in count mode, but the ISR doesn't fire and I don't know why (disclaimer, a second ISR is working to run the stepper motor timer).  I'm using an arduino to put out a test servo signal and my servo moves with it.  I connect the psoc to the servo signal and nothing.  From a hardware setup standpoint, the TCPWM is supposed to reset and start on a rising edge of the servo pulse and I have count enabled for that as well.  On the falling edge, it is supposed to capture and stop.  The clock is HFCLK / 1 = 24 MHz and it is a 16 bit counter, so at a count rate of 418 ns, it will take 24000 counts to get to 1 ms and 36000 to get to 1.5 ms and 48000 counts to get to 2 ms at which point the signal should be off.  The software side of this is pretty straightforward if the interrupt would trigger.  What did I forget to turn on or miss?


      Code snippet:




          Countme = ServoRead_ReadCapture();

          Flag = 1;



      int main(){

                              /* local variables */


          isr_1_StartEx(StepperMove);                         // setup timer interrupt sub-routine

          CyGlobalIntEnable;                                  /* Enable global interrupts. */


      top design:


      Thanks for any help or suggestions!