ADC noise TMS320F28335

bahman

I am using F28335 cheap and using ADC to get PWM signal but I'm getting noise from ADC conversion so the PWM signal not having constant width.

the ADC connected to stable power supply and any other unused analog pins and ADCLO are grounded.

Is it something normal or I can solve it?

Thank you

over 12 years ago

0 Igor Gorbachev over 12 years ago

Guru 20525 points

Hi Bahman!

I think these threads will be useful

http://e2e.ti.com/support/microcontrollers/c2000/f/171/p/264395/924719.aspx#924719

http://e2e.ti.com/support/microcontrollers/c2000/f/171/p/268446/937894.aspx#937894

http://e2e.ti.com/support/microcontrollers/c2000/f/171/p/269271/940713.aspx#940713

Regards,

Igor

0 bahman over 12 years ago in reply to Igor Gorbachev

Prodigy 130 points

Thanks for suggestions Igor

I have red those posts.

I'm getting almost +-5 % vibration and this cause vibration on servo connected to PWM output.

Please give me ideas how to reduce that?

Thank you

0 Igor Gorbachev over 12 years ago in reply to bahman

Guru 20525 points

Hi Bahman!

Have you some regulator at your system (for exampel P-regulator and some feedback)?

Regards,

Igor

0 Gautam Iyer over 12 years ago in reply to bahman

Guru 192875 points

Hi Bahman,

2 easiest way to tackle these problems are:

1. Use a RC filter before an ADC channel.

2. Use the averaging technique i.e. store the contents in an array and calculate the average value.

Whichever suits you the best, implement !

Regards,

Gautam

0 bahman over 12 years ago in reply to Igor Gorbachev

Prodigy 130 points

Hi Igor

I'm not using any feedback.

Thank you

0 Igor Gorbachev over 12 years ago in reply to bahman

Guru 20525 points

Hi Bahman!

I see. Then at first I would recommend you to try what mentioned by Gautam.

Regards,

Igor

0 bahman over 12 years ago in reply to Gautam Iyer

Prodigy 130 points

Hi Gautam

Using RC filter would not help because power source is fine. The averaging makes the signal stable it's a good idea but I am going to try that see if it's working fine.

I have used it to get average value of PWM input on ADC channel before.

Thank you

0 Gautam Iyer over 12 years ago in reply to bahman

Guru 192875 points

Good to hear.

Cheers,

Gautam

0 bahman over 12 years ago in reply to Gautam Iyer

Prodigy 130 points

Thank you guys for replaying and helping me.

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ADC noise TMS320F28335