Hall effect sensor - 480-5198-ND - Question

[ToonBlue]

Homework Statement

I am using the a hall effect sensor - model 480-5198-ND. I have tested this simple circuit using a LED and it is working. However, it is "ON" by default. Only when the magnet is near the hall effect sensor , it will be "OFF".

How do I make it such that it is OFF by default and ON only when the magnet is near the hall effect sensor?

Homework Equations

The Attempt at a Solution

http://[ATTACH=full]199957[/ATTACH]

 

[ToonBlue]

The A in my diagram means that it is connected to the LED.

 

[berkeman]

Follow it with a common-emitter NPN transistor stage to invert the output signal. Does that make sense?

 

[ToonBlue]

Can I have some explanation why it is able to invert the signal?

 

[berkeman]

A common-emitter NPN configuration is commonly used to invert a signal. You put your signal into the base through a resistor, and the collector and associated output resistor have the inverted signal on them. Just do a search for NPN common-emitter inverter circuit tutorial, and you should find what you need.

http://www.brown.edu/Departments/Engineering/Courses/En123/eqnTUTOR/common_emitter_inverter.jpg

 

[ToonBlue]

May I know how do I calculate the value of R1 and R2?