I'm using the hall effect sensor A1301EUA-T, I'm feeding it with 5V. At the VOUT output when there is no magnetic field there is 2.5V. When approaching the NORTH POLE of the magnet VOUT ranges from 2.5 up to 5v. When it approaches the SOUTH POLE of the VOUT magnet it varies from 2.5 up to 0v. To have a variation in VOUT from 0v to 5v I need 2 magnets, move one away and bring the other closer. My question is: how do I have a variation in VOUT from 0v to 5v approaching just one magnet, that is, I want it when I have no magnetic field close to the sensor I have 0v in VOUT?
Subtract 2.5 volts and apply a gain factor of two. This can be done quite easily with an opamp but it's likely you'll need a negative supply to reach precisely 0 volts and a positive supply greater than 5 volts to reach an output of 5 volts.