Hello, I am trying to find the right hall effect sensor to use it as a SWITCH with an MPC23017 I/O expander for a matrix "keypad". For multiple-key press i will use diodes like in the scheme below. http://www.musicfromouterspace.com/...ES/CONTROLLERS/images4/reeds_and_diodes_2.gif The hall switchs will replace the mechanical switchs and it will have to act as a normally open switch when there is no magnetic field present and it will need to close the circuit when a magnetic field is present. My question is. What kind o hall switch i need to use so i won't need to add other external components? What too look for in a datasheet to know that i got the right hall sensor?