Circuit diagram question - microcontroller input protection
You need an attenuator, not an amplifier (BJT). Here is a crude circuit. You may need a 4th diode depending on your MC input threshold. The zener voltage can be adjusted to get the input threshold to be what you want. Do you want >80V? or it that just typical. 

What is the spike width, you may want a small cap in parallel with the MC input to filter out spurious noise.







simulate this circuit &ndash; Schematic created using CircuitLab