Is there a way to take a signal from a phototransistor, filter out non 40 kHz square wave signals and then be able to read the strength of the signal with an ADC?
signal from phototransistor ---> filtering ---> if 40 kHz wave then read level of signal with adc as you would normal do with a phototransistor output
signal from phototransistor ---> filtering ---> if 40 kHz wave then read level of signal with adc as you would normal do with a phototransistor output