Magnet rangefinder

A system, comprising:

• a sense circuit, comprising:
• a radially-wound coil configured to produce a first magnetic field in response to a current applied to the coil;
• and
• a hall-effect sensor comprising a sensor output comprising a trip level, the radially-wound coil in fixed proximity to the hall-effect sensor;
• a power source, coupled to the hall-effect sensor, configured to provide power that alternates between on and off voltages to the hall-effect sensor;
• a magnet that produces a second magnetic field, the magnet configured to move in one or more directions with respect to the hall-effect sensor, the sensor output indicates proximity of the magnet to the hall-effect sensor in response to a combination of a strength of the first magnetic field and a strength of the second magnetic field at the hall-effect sensor exceeds the trip level;
• and
• a control circuit, coupled to the sense circuit, configured to:
• produce the current to the radially-wound coil;
• modulate the current to control the polarity of the first magnetic field;
• sample the current at a sample time the sensor output initially indicates detection of the magnet after the sensor output does not indicate detection of the magnet;
• and
• determine a sensed distance to the magnet from the sample.

A method, comprising:

• providing power comprising an on voltage for an on time and an off voltage for an off time to a hall-effect sensor;
• producing, by a control circuit, a current to a radially-wound coil;
• producing a first magnetic field in the radially-wound coil by modulating the current, the current providing a bias level for the hall-effect sensor in fixed proximity to the radially-wound coil, the hall-effect sensor comprising a sensor output;
• moving a magnet producing a second magnetic field within a detection range of the hall-effect sensor;
• indicating detection of the magnet, by the sensor output, in response to a combination of a strength of the first magnetic field and a strength of the second magnetic field exceeds a trip level of the hall-effect sensor, the trip level being higher than the bias level;
• sampling the current at a time when the sensor output initially indicates detection of the magnet after not detecting the magnet;
• and
• determining a sensed distance to the magnet from the sample.