If you are looking for a Hall effect sensor, be aware that many are digital only output (0 or 5V). If I understand what you want to do, you will want to make sure that the sensor has an analog output.
If you are looking for a Hall effect sensor, be aware that many are digital only output (0 or 5V). If I understand what you want to do, you will want to make sure that the sensor has an analog output.