There is some hysteresis in the range, where the release point is less than the operate value. 82 Analog Interfacing to Embedded Microprocessors Figure 3.24 The Hall effect. Hall effect switches come in two varieties: unipolar and bipolar, which are sometimes called nonlatching and latching. Bipolar switches have a positive (south pole) operate point and a negative (north pole) release point. Unipo- lar switches have a positive (south pole) operate point and a less-positive release point. The operate and release points vary with temperature. Both bipolar and unipolar switches typically have an open-collector output that has to be pulled up with an external resistor. Hall effect sensors are commonly available in three-lead packages similar to the TO-92 transistor package. The three leads are power, ground, and output. Typical supply voltages are 5 to 10v, although some sensors operate
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