Did you carefully follow the instructions in the Build Document? ->
---------------------------------------------------------------------------------------------------------------------
If you go through the following steps carefully, and in order, you will have a greater chance of
ending up with a detector that actually works. Do not proceed to the next step until you have solved
any problems encountered in the current step. If you get stuck at any stage during the build, then
seek help in the Geotech forums before moving on. Do not simply populate the whole board;
discover it doesn't work (which will be the most likely result) and then post in the forums: “I've
built the Minipulse Plus, and it's not working. What's wrong?”, as you will receive little sympathy
from other Geotech members.
To reiterate:
Please follow the instructions step-by-step.
---------------------------------------------------------------------------------------------------------------------
I suspect you've been a bad boy and populated the whole board before testing. If so, I would suggest reading each step now, and follow the test procedure. This should help to isolate the problem.
Regarding the threshold. It has been mentioned previously that the sensitivity is set to maximum, which means it does move from a position of slow ticking to a faster tick quite rapidly. If you want to adjust this, then you can try increasing the value of R35. Have a look at the original MiniPulse schematic. There was an internal trimmer between the opamp and R35, and a fixed resistor that's normally connected to -5V when the battery warning circuit is inactive. This trimmer allows adjustment of the threshold sensitivity
The "chatty" behaviour will only become evident if you have the threshold set to something higher than a very slow ticking. However, you won't miss any targets, as the tone increases very rapidly.