Hi Guys 
I have made frequency counters for pics before with or without frequency dividers, etc.
but always reading a lower voltage signal for radio and having to amplify it with a transistor or other amp.
Now I want to read frequency from a voltage 12-30 Volts from the collector of a medium power transistor MJE3055T,
and I’m not sure the internal clamping of the pic can be trusted that way.
I can think of a few methods and wanted ideas of others.
One way... current limiting resistor from the collector to a resistor divider, through to the pic pin,
or current limiting resistor from the collector through a external diode clamp to the pic pin,
or another transistor with it’s base connected via current limiting resistor to the collector,
and the emitter connected to the pic pin.
Do all of these sound viable? I do not want to influence much current or voltage of the circuit being measured.
Cheers, Art.
I have made frequency counters for pics before with or without frequency dividers, etc.
but always reading a lower voltage signal for radio and having to amplify it with a transistor or other amp.
Now I want to read frequency from a voltage 12-30 Volts from the collector of a medium power transistor MJE3055T,
and I’m not sure the internal clamping of the pic can be trusted that way.
I can think of a few methods and wanted ideas of others.
One way... current limiting resistor from the collector to a resistor divider, through to the pic pin,
or current limiting resistor from the collector through a external diode clamp to the pic pin,
or another transistor with it’s base connected via current limiting resistor to the collector,
and the emitter connected to the pic pin.
Do all of these sound viable? I do not want to influence much current or voltage of the circuit being measured.
Cheers, Art.