Low voltage PWM to logic level PWM
Base on the oscilloscope's response you can't be sure of the actual protocol of the sensor and you should watch up the sensor's datasheet. The sensor can be analog or its output can be based on current and not voltage in the case you can use any kind of current sensor or many other techniques. 

It is hard to offer the exact answers to the question due to lack of information. Any way there are several techniques which you can use to fulfill your purpose regarding to the relative frequency and variation of the voltages. 
First you can use the micro's ADC of course if the frequency is low enough. 
Also you can use transistor or high slew rate op-amp to read your signals. 
If you determined the signal's frequency and its voltage variation (if there is any) and the sensor's output's type, there could be more available answers.