Comparator input below V-
This may give you some ideas:







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Comparitor to handle negative voltages.


R3 sets a threshold between 0 and V+. If this is too coarse add series resistors at the top and/or bottom of the pot to narrow the range of adjustment for easier adjustment.
The trick of the circuit is to feed the non-inverting input from a potential divider, the top of which is connected to V+. In this example \$ V_A = V_+ - \frac {V_+ - V_{IN}}{2} \$ so the input voltage can range from \$ \pm V_+\$