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Electronics => Electronics => Topic started by: Razor Concepts on October 17, 2009, 04:58:01 PM

Title: Long ADC line filter
Post by: Razor Concepts on October 17, 2009, 04:58:01 PM

I want to mount a standard analog-out temperature sensor some distance away from the microcontroller, say three feet. I remember something about long ADC lines not being good, how can I add capacitors or something to help stabilize it?

Title: Re: Long ADC line filter
Post by: madsci1016 on October 18, 2009, 12:04:03 AM

3 feet is no big deal. Its 30 feet you might see some issues.

I haven't read much about why this would be bad, but I assume its line loss they are worried about. Since load (the mictrontrollers ADC) would not change, i'd say if you are worried about line loss, just measure the sensor side and microcontroller side of a long wire, and program in an offset to account for this.

Title: Re: Long ADC line filter
Post by: Soeren on October 18, 2009, 01:46:03 AM

Hi,

The real problem with high impedance lines is induced noise.

For long lines, (i.e. a few inches and beyond), you might wanna use 4-20mA current loop or a similar low impedance scheme.