Mastering Internet of Things

Canceling noise

Since the digital PIR sensor already has error correction built into it, we will only focus on how to cancel noise from our analog light sensor. Noise can be canceled electronically, using, for instance, low-pass filters. It can also be cancelled algorithmically, using a simple averaging calculation over a short window of values. The averaging calculation will increase our resolution, at the cost of a small delay in the output.

If we perform the average over 10 values, we effectively gain one power of 10, or one decimal, of resolution in our output value. The value will be delayed 10 seconds, however. This algorithm is therefore only suitable for input signals that vary slowly, or where a quick reaction to changes in the input ...