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Step 6Add Hall effect sensor
The Hall effect sensor is for detecting whether the door is in the center, i.e. within the range that closing the locks makes sense. There are other solutions possible, such as mechanical/optical rotary encoders, contact sensors, beam break sensors. The main reasons for choosing a Hall effect sensor were that it does not add friction, it can be covered entirely, and I also was just curious how they work.
I did not want to put magnets on the door because that would make it heavier, so instead I put the switch on the door and the magnets in the door post. I had to use thin, very flexible wire otherwise the rigidity of it would push the flap off center. The sensor and wire is simply taped to the Plexiglas. I have two little magnets in the door post. At the closest point the sensor and magnets are 5mm apart. The range is about 3cm.
Connect the signal pin of the Hall sensor to pin 4 and to through a 100 ohm resistor to 5v. Connect ground pin to the other grounds and the vcc pin to 5v. Add an LED to digital pin 7 with the appropriate resistor (used a green one with a 220 ohm resistor).
Download Hall_effect.pde to test this part of the system.
I did not want to put magnets on the door because that would make it heavier, so instead I put the switch on the door and the magnets in the door post. I had to use thin, very flexible wire otherwise the rigidity of it would push the flap off center. The sensor and wire is simply taped to the Plexiglas. I have two little magnets in the door post. At the closest point the sensor and magnets are 5mm apart. The range is about 3cm.
Connect the signal pin of the Hall sensor to pin 4 and to through a 100 ohm resistor to 5v. Connect ground pin to the other grounds and the vcc pin to 5v. Add an LED to digital pin 7 with the appropriate resistor (used a green one with a 220 ohm resistor).
Download Hall_effect.pde to test this part of the system.
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