A Hall Effect sensor such as the UGN3503UA Hall Effect Sensor http://www.jaycar.com.au/products_uploaded/ZD1902.pdf can be used to measure magnetic fields. This sensor requires +5V, this is available from the XO's USB connectors. | A Hall Effect sensor such as the UGN3503UA Hall Effect Sensor http://www.jaycar.com.au/products_uploaded/ZD1902.pdf can be used to measure magnetic fields. This sensor requires +5V, this is available from the XO's USB connectors. |