Speed Sensor Circuit

This circuit is powered by the low voltage module, which supplies 12V DC from a buck converter connected to the 48V battery. A photo interrupter is used to sense the rotational speed of an aperture wheel connected to the shaft of the drive motor. The wheel has 20 holes spaced evenly around its circumference, and as the motor spins the holes will allow light from the diode to pass to the transistor as a brief pulse. This pulse allows the transistor to turn on and off, sending a signal to the Arduino that rapidly switches from 0 to about 4.8V. This voltage was achieved by creating a voltage divider. The aim of the divider was to be close to 5V, since that is the voltage accepted by Arduino's analog input for the purpose of mapping. The frequency of the signal from this circuit will be measured and used to calculate RPM of the motors. R1 is used to limit the current running through the diode. The capacitor is used to filter out some of the noise to provide a clean output signal.