PWM and TIMER1 problem in stm32f4

[vss01]

Posted on February 22, 2016 at 00:13

Hello,

I need to generate sin wave using STM32 uC. Now here comes the problem. I am able to obtain the required sin wave with the required frequency and the required amplitude however there are other (more than one) frequency components.After spending some time, I think I have pinpointed my problem down to having something related to 'jitter' in the PWM or phase noise because of a mismatched PWM frequency and sample rate of the lookup table.What do you think? Any help would be appreciated!

[Tesla DeLorean]

Posted on February 22, 2016 at 01:47

Ultimately the machine does what you tell it too, unfortunately I can't see from this what you're physically instructing the machine to do.

Instead of programming the timer, write all the data you generate to a file, and the plot and review that.

[vss01]

Posted on February 23, 2016 at 22:55

I have a sinusoidal lookup table that contains only a 50Hz that I'm using, however I don't know how its not only 50Hz on the capacitor of the lowpass filter. If you need details of the setup see my previous post. 

Thanks!

[Tesla DeLorean]

Posted on February 24, 2016 at 02:17

Ok, the key detail missing is the code, something I can compile and follow the logic, I'm not looking to recreate or resolve this for myself.

[vss01]

Posted on February 24, 2016 at 21:22 Find attached the files and thank you. ________________ Attachments : main.c : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006I13I&d=%2Fa%2F0X0000000bhR%2FZ9Pbu2sDLdWk3IeVGx.JHTUpa2nko_fo7p3eSTbsSAc&asPdf=falsestm32f4xx_hal_msp.c : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006I0sq&d=%2Fa%2F0X0000000bhP%2FozoUyJ5fBuW1ngpgYsZsZfX1.nvRCwO5bNeYGMxZ478&asPdf=falsestm32f4xx_it.c : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006I13D&d=%2Fa%2F0X0000000bhO%2F1ieOP3tb6MOClulId5ylIlKAXPOqUvOQylZ_S39wr3A&asPdf=false

[Tesla DeLorean]

Posted on February 24, 2016 at 21:47

Your update interrupt looks really dodgy

//update sin sample on overflow only if(htim8.Instance->CNT > 3000){ //... And 4200 is half of 8400 Needs to be

if (__HAL_TIM_GET_IT_SOURCE(&htim8, TIM_IT_UPDATE))
{
__HAL_TIM_CLEAR_IT(&htim8, TIM_IT_UPDATE);
if (sin_index >= 200)
sin_index = 0;
__HAL_TIM_SetCompare(&htim8, TIM_CHANNEL_1, 4200 + sin_wave_50hz[sin_index++]); //4200 = PERIOD/2 = 8400/2
}

[vss01]

Posted on February 24, 2016 at 22:14The interrupt is entered on an underflow or an overflow. I want to update my sample only on overflows or else i will be updating it twice per 100E-6. That's why I have if(htim8.Instance->CNT > 3000) to make sure i update it only once, and that is on an overflow.

[Tesla DeLorean]

Posted on February 25, 2016 at 00:45

I'm not sure how it is going to underflow, the update occurs once per period, ie at 10 KHz

Realistically this could be done with DMA and be completely autonomous.

[Tesla DeLorean]

Posted on February 25, 2016 at 02:15

Other thoughts, the Period should be N-1, the TIM8 will run at 168 MHz

Attached is a .HEX that drives PC6 (TIM8_CH1) and PA7 (TIM8_CH1N), this should generate a 50 Hz sine wave via a 10 KHz PWM. Please see if this generate the wave form you expect. ________________ Attachments : PWM8_50HZ_REL1.hex : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006I12Q&d=%2Fa%2F0X0000000bhN%2FAlv3B8cCDLf9hMbKFwEV.s6SQFd0RrtTqBJiz4KPsl8&asPdf=false

[vss01]

Posted on February 25, 2016 at 07:13

Underflow can occur because I have my timer running in up-down mode counter.