Hello evrybody,
I would like measure the image of the current of a brushed dc motor with the analog input of a MSP430 but the signal is noisy because of the brushes commutation . I don't need a realy flat signal because I will do an average with multiple sampling , but I need something more clean. Could you give me some advices about the capacitor value or the RC filter to put in place . I don't know realy how implant this filter.
Regards

 

Hello,

Depending in how fast you want to see changes in the current, you could use a low-pass filter on the current signal.

Bertus

 

Hello,

Depending in how fast you want to see changes in the current, you could use a low-pass filter on the current signal.

Bertus

betwin 30 to 50 ms , more rapidely , it's not necessery, but have you some advise about the low pass filter calculation ?

 

Hello,

Have a look at this page of the eBook:
https://www.allaboutcircuits.com/textbook/alternating-current/chpt-8/low-pass-filters/

A filter of 33.33 Hz will give you a responce time of about 30 mS.

Bertus

 

Hello,

Have a look at this page of the eBook:
https://www.allaboutcircuits.com/textbook/alternating-current/chpt-8/low-pass-filters/

A filter of 33.33 Hz will give you a responce time of about 30 mS.

Bertus

Wouaw ! with a 75k Ohm resistor and 68 nF it's perfect for my application . Thank You Bertus

 

If a single-pole RC filter does not reduce the noise sufficiently then you may need to use an active filter with more poles such as this 3-pole, low-pass active filter.
You would probably want to use the Bessel type for your requirements, since it has little overshoot with a step (fast changing) input.