ADC reads wrong when the fan active

zydis · Joined: 10 Aug 2015 Posts: 3

Hi, I have a problem when I read current from adc. My circuit is below to read current.

http://4.bp.blogspot.com/-R6EqqPt2H9o/USQqzV2zr1I/AAAAAAAAAB4/shSBHjwe0R0/s1600/ak%C4%B1m+okuma.png

When I read current from the out of device that have a fan, it works well, but when the fan working current is stable but reading from adc is changing. Do you have any idea for solution?

Mike Walne · Joined: 19 Feb 2004 Posts: 1785 Location: Boston Spa UK

What do you mean by "current is stable"?
Have you probed with a scope?
What sort of fan are you using?
etc...............

Mike

EDIT You're not showing any decoupling caps.

temtronic · Posted: Tue Sep 15, 2015 5:13 am

What type of fan? A brush type fan will produce a LOT of EMI and a BLDC fan draws current in pulses. A DVM will not show this though an Oscilloscope will. It's possible the ADC reads this noise or EMI.

What is your ADC reading/display program ? You should read at least 8* then average the reading. Olympic average is 'smoother'. If you have time, take 16 readings and then average.
Since your load is a fan, it doesn't require microsecond ADC response so using 16 rdgs/avg will give better (smoother) results will no overall loss of performance.
If you read in binary multiple (4,8,16,32) the math is a lot faster and easier on the PIC.

Fans are like temperature sensors and door switches where 1/10th /second per reading is more than fast enough.

Jay