I'm using an atmega328p with 2 ADC input signals, one to monitor the battery and one current sense for my DC motor in order to detect jams. The datasheet says that frequencies above f_adc/2 should be removed. Since I'm running at 8MHz with a prescaler of 128, I'd need to cutoff above roughly 30kHz. I'm doing this using an LC filter with L=56uH and C=470nF. Using an online calculator this should have the correct cutoff frequency. While reading online there are a few things I became confused about.
- In this post it says that f_adc is the sample rate instead of ADC clock, since it doesn't even get sampled at 1Hz, it seems like this would lead to very large inductance/capacitance values?
- In the same thread it is often mentioned that no filter is needed except if it is a noisy environment. Given the fact that I'm using a DC motor, it seems that this would be the case?
- In this post it is said that noise problems are generally part of another problem and, other than in the case of long cables, is probably not solved by filtering adc signals.
Given this information, I'm not exactly sure what reasoning to use to calculate the values for the LC filter, or that I even need one, or maybe just a cap or RC filter? Any clarification would be greatly appreciated.
Here is 'the schematic in case it helps clarify things.