Hello,
Our team wants to connect a 3-wire (ground, power, and signal) hydrophone buffered by an op-amp circuit to the AudioMoth Dev and we were wondering how we could do so. The application notes explain how to connect buffered hydrophones that run off 2 wire plug-in power, but no information for 3-wire hydrophones. We experimented and realized that we can hold the signal pin down with a 1K resistor. While this works, we are hoping to deploy many many of these around Greenland for months at a time and we don’t want to waste power. Is there a more power efficient way to make this work?
Hi, If you add this circuit between the amplifier and the AudioMoth it will work fine. The capacitor may not be necessary if there is one included on the output of the amplifier. The 2K7 resistor ensures that the input to the AudioMoth is correctly loaded. The AudioMoth supply is only enabled when recording so this won't cause any additional current drain between recordings, and during recordings it is quite small - just 500uA - the same as an external electret capsule microphone. For a full-scale output at normal gain settings you need about 10mV peak-to-peak input signal.
It is also possible to use the voltage at the input of the audiomoth 3.5mm jack to switch a MOSFET to power on and off the hydrophone power and amplifier. This voltage will go from zero to 1.5V when a recording is being made, meaning that there is no additional drain from the hydrophone amplifier between recordings.
Alex