Page 75 - Handbook of Biomechatronics

70 Jeff Christenson

Fig. 10 (A) Example of a light-dependent resistor and (B) circuit diagram with a light-
dependent resistor. As the intensity of the light sensed varies, the brightness of the light
changes.

3.4 Hall Effect Sensor
A Hall effect sensor is an electrical sensor which responds to change in a
magnetic field. Named after Edwin Hall who is credited with first observing
a voltage potential across a current carrying conductive plate in the presence
of a magnetic field in 1879 (Milano, 2009). In the sensor, there is a thin rect-
angular piece of semiconductor which constantly is carrying a current when
the sensor is turned on. As a magnetic field is introduced, the electrons pass-
ing across the plate deviate from the center due to the Lorentz force. The
electron deviation creates a voltage difference across the two ends of the
plate which is proportional to the electric field (Fig. 11).
There are several types of Hall effect sensors (Allegromicro, n.d.). On/off
Hall effects are used for binary signals. If the magnet is close to the sensor, a
high voltage is output. If the magnet is far away, the voltage is low.

Fig. 11 Hall effect sensor diagram. When no magnetic force is influencing the sensor,
the current, represented by the dashed line, remains in the center (left). When a
magnetic field is introduced, the electrons deviate from the center (right).