I sometimes enjoy the high frequency sounds of the coqui, but sometimes it's so high i actually can't hear it at all. I remember a former version of the coqui that was slowed down so much you could hear the separate clicks and the pitch was lower. On that one, the speed of clicking indicated the relative conductivity you were measuring. I'm wondering how to do this? Thanks!
I'm not positive, but since the Coqui is measuring resistance (which reveals conductivity) as in this diagram: https://publiclab.org/notes/donblair/09-30-2014/coqui-bbv1-0#Schematic
...i would guess that you could add a resistor to one of the probes, so basically you'd be measuring the resistance of the water PLUS the resistor, and that this would make the frequency lower, and so the pitch lower. But you'd have to try it out, my Coqui is not working right now!
I was also able to confirm that adding a resistor in-line with one of the probe wires lowered the frequency! Much lower and less annoying!
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Changing the frequency range would require either changing the duty cycle of the 555 or modulating the amplitude. I think the the probe (resistor) is modifying the amplitude. If you want to lower the range you could wire in a potentiometer on pin 5 (control) on the 555 chip. There is a good description here http://www.learnabout-electronics.org/Oscillators/osc44.php
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