Copy of frequency recognizer

This circuit shows the use of a low-pass filter. On the left-hand part, a simple non-inverting adder adds a base signal (5V, 1kHz) and an artificial low-voltage high-frequency noise (500mV, 100kHz). On the right-hand side of the schematic, the low-pass filter filters the signal. The gain is equal to -R2/R1. The cutoff frequency is defined by f=1/(2*pi*R2*C2). In this example, it has been set to around 10kHz, 10 times the base signal's frequency.