I've designed a 5th order Sallen Key High Pass Filter (HPF) (Passband>=1KHz) that feeds into a LM386 amplifier into an 8 ohm speaker. The input signal to the filter is a probe tip which picks up stray frequencies inside walls and other nearby metallic objects or antennas and sends that signal to the amplifier to generate a tone so the user can detect if something is present. The main board and filter board is powered by a 9 volt battery.
I tested the HPF board independent of the main circuit board and all works to spec. I then integrated the HPF into the main board and used a 1KHz tone generator connected between the tip and GND of the circuit and I can hear the tones perfectly without any distortion.
I then connected one end of the tone generator to a metal plate so it can radiate that same frequency so I can test if the probe works as intended to be used. This is where the probe circuit has failed to work and I can't hear anything at all.
Any input to this issue is appreciated as its the first time I've ever encountered this 10 years as an engineer.
I tested the HPF board independent of the main circuit board and all works to spec. I then integrated the HPF into the main board and used a 1KHz tone generator connected between the tip and GND of the circuit and I can hear the tones perfectly without any distortion.
I then connected one end of the tone generator to a metal plate so it can radiate that same frequency so I can test if the probe works as intended to be used. This is where the probe circuit has failed to work and I can't hear anything at all.
Any input to this issue is appreciated as its the first time I've ever encountered this 10 years as an engineer.