MSP430FR5994: Using a comparator to measure the time to hit a voltage range

Hi Barry,

You can start with the code example in the MSP430 driver library. These examples shows you the steps to configure the device and COMP to make it work.

http://dev.ti.com/tirex/#/?link=Software%2FMSP430Ware%2FLibraries%2FDriver%20Library%2FMSP430FR5xx_6xx%2FExample%20Projects%2FCOMP_E%2FCOMP_E%2FCOMP_E

Best regards,

Jovi He

Hi Jovi,

This was really helpful in setting up my code. I'm currently having some trouble working with the interrupt.

I need the interrupt to execute two separate sequences. When my capacitor's voltage first hits the threshold (3.2V), I need the eCOMP_ISR to toggle the charging pin then reset the timer. I then need the eCOMP_ISR to trigger when it hits the low threshold (1.1V), and I need it to tell me how long it took (based off my counter) to discharge to that voltage.

I believe that the conditions in the if-statements in the eCOMP_ISR are wrong. It seems to immediately enter the second if statement after exiting the first. The code for the interrupt is posted below. Can you check to see if the conditions are correct and point me in the right direction?

#pragma vector=COMP_E_VECTOR
__interrupt void COMP_E_ISR(void)
{
//Toggle the edge at which an interrupt is generated
Comp_E_toggleInterruptEdgeDirection(COMP_E_BASE);

//Clear Interrupt flag
Comp_E_clearInterrupt(COMP_E_BASE, COMP_E_OUTPUT_INTERRUPT_FLAG);

if(CECTL1&CEOUT){
capCharged=1;
salinityTimer=0;
P8DIR &= ~IR_LED; //start capacitor discharge
}

if(!(CECTL1&CEOUT) && (capCharged==1)){
salinityDischargeTime = salinityTimer;
salinityFunctionDone=1;
}

//Toggle P3.5 output pin.
GPIO_toggleOutputOnPin(GPIO_PORT_P3, GPIO_PIN5); //toggle output pin port 3 pin 5
}

Thanks,
Barry

Barry,

Please check the timing constant of the cap discharge and the MCU running speed. If the capacitor discharge time is few CPU cycles, then it will execute the second statement immediately.

Best regards,

Jovi He 

The capacitance is about 30 pF and the resistance is 5.1 Mohms. The time constant should be 153 microseconds. The microcontroller is using an 8 MHz clock. The discharge time is much greater than a few CPU cylces. Since you didn't mention the if-statement conditions, can I assume those are correct?