Group Actions
Engagement
  • Author Author: Jan Cumps
  • Date Created: Date Created
  • Views 409 views
  • Likes 5 likes
  • Comments 25 comments
Related
Recommended

PID temperature controller for the EasyL1105 MSPM0 board - Pt. 3: PWM

Jan Cumps
PID temperature controller for the EasyL1105 MSPM0 board - Pt. 3: PWM

  designed a development kit for the recent Texas Instruments MSPM0 microcontroller series. 
This 4 part blog series documents the steps to design a PID temperature controller. Part 3: add PWM to generate a PID controlled output.

image
(post that introduces the kit)

Goal of this 3nd post

not a goal of this post: have the PID regulation working 100%.

Set up PWM SysConfig

The code uses timer TIMG1, channel 0, to drive PA26. There's no interrupt involved. The duty cycle gets adjusted in the regulation loop.

At this point, I have set the PWM period count to 65535, in an attempt to have the output range identical (but 32768 offset) to the input. 

image

image

Code

note: this design doesn't regulate perfectly yet. At this point in the blog series, all modules are in place and they are tied to the PID. But finetuning PID parameters, input, output, ADC and PWM settings is for post 4.

void perform_pwm() {
    DL_TimerG_setCaptureCompareValue(PWM_0_INST, i32_Output_PID + 32768,
        DL_TIMER_CC_0_INDEX); // update ccr0 value  
}


int main(void) {
    SYSCFG_DL_init();

    // /* timer 5 interrupt ticks per second */ 
    // /* Enable Timer0 NVIC */
    NVIC_EnableIRQ(TIMER_0_INST_INT_IRQN);

    NVIC_EnableIRQ(ADC12_0_INST_INT_IRQN);
    gCheckADC = false;

	/* Initialize the parameters of PID */
	Initialize_PID_Parameter();

    /* Start PWM */
    DL_TimerG_startCounter(PWM_0_INST);

    /* Start Timer counting */
    DL_TimerG_startCounter(TIMER_0_INST);    

    while (1) {
        if (perform) {
            perform = false;
            DL_GPIO_setPins(GPIO_GRP_LEDS_PORT,
                GPIO_GRP_LEDS_PIN_LED_GREEN_PIN);

            perform_adc();
            
            perform_pid();

            perform_pwm();

            DL_GPIO_clearPins(GPIO_GRP_LEDS_PORT,
                GPIO_GRP_LEDS_PIN_LED_GREEN_PIN);
        }
    }
}


void perform_pid() {
    /* Execute PID control in every TM0 interrupt. */
    i32_Output_PID = PID(&PID_Var, i32_Target_Command, gAdcResult);
}

If you compare the perform_pid() with the one from the previous post, you 'll see that it now uses ADC as feedback, and output to drive the PWM.

Demo circuit

I used the same (random) low pass filter as in  MSP432 and TI-RTOS: PID Library Part 2 - Real World Example , to turn the PWM into a DC signal.

image

The filter sits between PWM out  (P26) and ADC in (PA25).

ccs project for EasyL1105: pid_EasyL1105_20251002_02.zip

Related posts

Parents

  • This is the second time I've seen PID referenced and I am confused.

    PID was a Process IDentifier assigned by an operating system. Now it is a Proportional-Integral-Derivative (PID) controller, a type of control system commonly used in automation.

    Can someone explain this new coin of PID?

  • in reply to colporteur

    It's a Control Technique algorithm. A function that will try to regulate a process' output, in relation to a desired setting. First used in 1911.

    It requires that you give it feedback on the current output (e.g.: a sensor value).

    The algorithm uses 3 tuning parameters, P, I and D, to try and make a smooth regulation.

Comment
  • in reply to colporteur

    It's a Control Technique algorithm. A function that will try to regulate a process' output, in relation to a desired setting. First used in 1911.

    It requires that you give it feedback on the current output (e.g.: a sensor value).

    The algorithm uses 3 tuning parameters, P, I and D, to try and make a smooth regulation.

Children
  • in reply to Jan Cumps

      I have only ever heard of PID referencing control systems (40-ish years).  In the 1980's and 90's, we typically only were able to adjust the Proportional - also called Gain.  There may have been another term that I can't think of right now.  Integral and Derivative were set in firmware.  As technology advanced, we were allowed to adjust the I & D.  I can't count the number of systems I fixed by just turning the P down to 30% to 35%.