Hi,

I don't seem to understand the circuit attached. The comparator U2 is acting like some kind of relaxation oscillator, right? It's weird that U2 is powered from GND and -12V. As far as I know this circuit is used to inject an AC signal to the test coil when PB1 is pressed. But how does it exactly work?

 

hi BE,
Where did you find the circuit.?
A link to a web site or some explanation on how the circuit is used would be helpful.
E