Encoders

The raw signal coming out of the phototransistor is not strong enough to go into microcontroller. Furthermore, it is
drifted due to the noise from the motors (which are right beside the encoders). It turns out that the main effect of
this noise source is swinging the average voltage up and down at a frequency around 3 Hertz.

A low pass filter is used to get rid of this noise while still able to capture the wheel speed at the low side (lowest
speed: 30 RPM or 30.180/60=90Hz)

The signal is then amplified 10 times to be strong enough to go through a Schmitt Trigger then to the microcontroller.

Virtual ground: is chosen at 2.5 V. It is used to the low pass filter, analog amplifier and comparator circuits.


Comparator circuit: Simple calculation gives us V+=
V-=2.5-2.5*(10K/100K)=2.25V

By experiment, these thresholds are enough to give a clean signal event at the longest range